6 construction - Marley Pipe Systems

Transcription

6CONSTRUCTION
Y o u r
Flat elastomer gaskets without steel inlays frequently leak at higher pressures, e.g. during pressure testing, therefore, the use of
armoured gaskets with a convex cross-section is recommended
particularly when the pressure (operating pressure) comes close to
the pipe's pressure rating. An additional improvement in the level
of sealing is obtained when the inside of the gasket has the form
of an O-ring.
V a l u e
P a r t n e r
6.3.2.3 Push-fit Connection
A push-fit connection is the general term for all spigot and socket
connections and is described in the following section.
Figure 6.15 Push-fit spigot
O-rings and double chamber gaskets are recommended in high
pressure pipelines, particularly when vacuum conditions may
occur. Gaskets shall not reduce the inside diameter of the pipe nor
allow fissures to occur, allowing fluid to penetrate the seal; with the
risk of sedimentation.
During assembly, care must be taken to ensure that the bolts are
tightened evenly and the gasket and sealing surfaces are clean.
Table 6.4 shows the standard values for the bolt torques in flange
joints.
Figure 6.16 Cross-section of a connection with a push-fit socket
Standard bolt torques in flange joints of thermoplastic pipes (DVS
2210 Part 1)
Table 6.4 Bolt tightening torques for flat, profile and O-ring
gaskets
Bolt tightening torque (Nm)
de (mm)
DN (mm)
Flat ring gasket
Profile gasket
O-ring gasket
(pacc ≤ 10 bar)
(pacc ≤ 16bar)
(pacc ≤ 16 bar)
20
15
15
10
10
25
20
15
15
15
32
25
15
15
15
40
32
20
15
15
50
40
30
15
15
63
50
35
20
20
75
65
40
20
20
90
80
40
20
20
110
100
40
20
20
125
100
40
20
20
140
125
50
30
30
160
150
60
40
35
180
150
60
40
35
200
200
70 (1)
50
40
225
200
70 (1)
50
40
250
250
80 (1)
55
50
280
250
80 (1)
55
50
315
300
100 (1)
60
55
355
350
100 (1)
70
60
400
400
120 (1)
80
65
450
500
190 (1)
90
70
500
500
190 (1)
90
70
560
600
220 (1)
100
80
630
600
220 (1)
100
80
Push-fit and expansion sockets
The seal of a push-fit or expansion socket pipe connection is
achieved by applying the forces of a sealing element to the connecting pipe or fitting. Furthermore, the internal pressure helps to
strengthen the radial sealing force; small pipe deflections can be
tolerated, as well as longitudinal movements equal to the distance
between the socket and seal seat.
Socket connections should only be used in pressure applications
involving pipe systems that are not subjected to underpressure;
use is to be avoided in pipe systems subject to underpressure and
another jointing technique selected.
Figure 6.17 Functional principle of the expansion socket
(1) for Pacc ≤ 6 bar
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6CONSTRUCTION
Y o u r
6.3.2.4 Unions
V a l u e
P a r t n e r
Figure 6.21 Compression principle
Figure 6.18 Screw-thread joint
6.3.3 Non-detachable Connections
6.3.3.1 General
Figure 6.19 Cross-section of a union
Non-detachable jointing techniques are the most commonly used
connection techniques in PE pipe construction. Welding is an extremely important form of connection used for PE jointing in plastic
pipe construction and has therefore been focused on in this manual
in Section 6.4.
6.3.3.2 Welding
Welding is of great significance in pipeline construction as well as
in the production of PE lines, tanks and special welded components. The welding techniques described in Section 6.4 are based
on the SANS 10268 series of process standards and ISO 21307
which have been adopted either directly or in revised forms.
These types of connections are used in water pipelines as well as
in transitions from plastic pipes to other materials. The ease of assembly makes them a particularly useful connecting technique for
small pipe sizes. However, temperature effects may restrict their
application in pipe systems due to the behaviour of plastic pipes;
each application must be carefully analysed.
6.3.2.5 Compression fitting
Compression fittings are a quick and easy manner to join pipes in
which a pressure chamber contains a sealing ring, and screwing in
the fitting causes the sealing ring to be clamped against the pipe.
NBR O-rings are used to seal against the PE pipes and special
compression rings can be used to connect PE pipes with other
types of material, such as PVC-U, PP, PE-X copper, lead and steel.
Compression fittings are used in swimming-pool systems, for potable water distribution, irrigation and telecommunications, as well as
in the mining industry and horticulture.
Figure 6.20 Compression fitting
6.3.3.3 Gluing
To date, gluing has not been used in PE pipe construction because
the characteristics of polyolefin make them unsuitable for glued
connections. Due to their "waxiness", their surfaces are not softened by adhesives. Special multi-component adhesives do allow
limited adhesion to be formed that cannot be subject to mechanical
loads and are technically irrelevant.
6.3.3.4 Push-fit socket end thrust bearing
Push-Fast is a unique spigot and socket type water jointing system
that combines the benefits of PE pipes with the ease of conventional push-fit joints. Unlike most spigot and socket type systems,
Push-Fast has a specially designed and patented socket, which
incorporates a tough thermoplastic 'grip' ring located in a tapered
groove. This allows the joint to resist end-thrust generated by the
internal pressure and eliminates the need for anchors or thrust
blocks.
202
6CONSTRUCTION
Y o u r
V a l u e
P a r t n e r
6.4 WELDING POLYOLEFINS
Figure 6.22 Section through assembled Push-Fast joint showing
grab ring and sealing
6.4.1 General
Plastic pipes can be welded using various welding techniques;
however, not every welding method is suitable for welding polyolefins. Therefore, when designing a plastic pipe system, it is important to understand what welding techniques are available and
their suitability early in the design process. The choice of the most
appropriate welding procedure is influenced by the following factors: economics, the construction of the pipe system, external and
internal influences on the system, as well as local conditions.
Push-Fast ends can easily be butt welded to pipe lengths and coils;
it is quick and easy to install, suitable for underground pipe systems
in subsidence areas and for installations in limited space situations;
the pipe system is ready for service immediately after assembly.
The performance of the Push-Fast joint depends on the efficiency
of the seal between the elastomeric sealing ring, the pipe and the
socket. Any damage to the pipe or fittings or the presence of dirt or
grit will adversely affect the performance of the joint.
Figure 6.23 shows the welding practices most frequently used with
plastics. The grey highlighted frames indicate the welding techniques usually employed for the welding of PE in plastic pipe construction. In practice, the welding methods most frequently used to
connect PE pipe components are butt welding and
electrofusion.
Figure 6.23 Welding techniques
Plastic welding techniques
Hot gas
welding
Friction
welding
Heatedtool welding
Hand welding
Direct
Indirect
Speed welding
butt-welding
Impulse
welding
Overlap welding
Groove
welding
Contact
welding
Extrusion welding
Fold welding
Infra-red
welding
Socket
welding
Overlap
welding
Electrofusion
Wedge
welding
Blade
welding
203
High-frequency
welding
Ultrasonic
welding
6CONSTRUCTION
Y o u r
6.4.2 Welding Procedures
6.4.2.1 Socket welding
Description
Socket welding, also known as socket fusion, resembles butt welding in its technique. The process is described in detail in the relevant standard SANS 10268-1.
In socket welding, both the spigot and socket are heated simultaneously. After the heating process, the socket of the fitting is pushed
over the spigot end of the pipe and pressure applied. The essential
difference with butt welding is that the fusing of the two surfaces
which are connected is in an overlapping manner. Therefore, one
side of the heating element possesses a form on which to mount
the socket (heating the spigot) and the other side, a form into which
to plug the spigot (heating the socket), see Figure 6.24.
Figure 6.24 Socket welding
V a l u e
P a r t n e r
• The welding surfaces are mechanically prepared immediately before welding using a scraper, grater or peeler to remove the oxidation layer.
• The spigot is bevelled as indicated in Table 6.15 and shown in Figure 6.25.
• The connecting surfaces of the pipes or fittings are prepared according to the manufacturer’s recommendations.
• Avoid forcing the end of the pipe against the body of the heating tool.
• For welds performed without machinery, the insertion depth equal to distance (E) in Table 6.5 must be marked on the pipe.
• The joining surfaces must be free of grease and dust; the socket must be thoroughly cleaned on the inside and the spigot on the outside using a degreasing agent, e.g. industrial alcohol, and absorbent, non-fraying and uncoloured paper. The same applies to the heating element.
• The welding work site must be protected from atmospheric conditions.
• No welding work shall be performed when the ambient temperature is below +5°C without taking special measures, e.g. protection by a tent; the temperature in the immediate proximity of the welding process shall not vary by more than 10°C.
• The functional capacity of the machines and equipment shall be tested prior to welding and the welding parameters checked. The temperature of the heating element for PE is 250-270°C.
Table 6.5 Weld preparation phase for pipe ends
The dimensions of the heating elements for the elements to be
welded are designed so that the joining of the elements creates a
welding pressure. Pipes up to a diameter of 50mm may be welded by hand, larger diameters up to and including 110mm must be
welded with appropriate apparatus.
Pipe diameter de (mm)
Pipe phase b (mm)
Insertion depth E (mm)
16
2
13
20
2
14
25
2
15
32
2
17
40
2
18
50
2
20
63
3
26
75
3
29
90
3
32
110
3
35
125
3
38
Figure 6.25 Pipe phase in socket welding
Socket welding process – preparation
The areas to be fused in welding must be carefully prepared in accordance with the rules that follow. The preparation of the welding
surfaces in pipe construction is critically important and must always
be complied with:
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6CONSTRUCTION
Y o u r
2
3
4
5
Outside pipe
diameter (mm)
Heating
SDR 11 - SDR 17
(sec)
Conversation
(maximum time)
(s)
Cooling fixed
(s)
Cooling total (min)
16
5
4
6
2
20
5
4
6
2
25
7
(1)
4
10
2
32
8
(1)
6
10
4
40
12
(1)
6
20
4
50
12
(1)
6
20
4
63
24
(1)
8
30
6
75
30
15
8
30
6
90
40
22
8
40
6
110
50
30
10
50
8
125
60
35
10
60
8
P a r t n e r
6.4.2.2 Change over
Table 6.6 Standard values for socket welding of PE pipes and
fittings under atmospheric temperature of 20°C and moderate
measurable air current
1
V a l u e
Figure 6.26 Butt welding jointing technique
Description
Butt welding is a very reliable and economical jointing technique in
which a specialised machine is required to create the non-detachable joint; it is very suitable for the prefabrication of pipe elements
and the construction of special fittings.
(1) If wall strength is too small, welding is not advisable
Execution
To heat the pipe to be welded, it is pushed into the socket heating
element of the heating tool up to the mark designating the welding zone and held in place; likewise the fitting is simultaneously
pushed onto the spigot. The heating period specified in Table 6.6
then begins, during which the pipe must not rest against the end of
the heating socket.
On completion of the heating period, the parts to be welded are
quickly removed from the heating device and immediately pushed
together, without twisting, up to the stopping mark. In manual welding, the joining parts must be held in place for the period specified
in Table 6.6. The joint must not be subjected to mechanical loads
until after the cooling period. The heating spigot and heating socket
are cleaned after every welding procedure using non-fraying paper
and an appropriate cleaning agent, e.g. industrial alcohol.
In butt welding, the welding surfaces (ends) of the components to
be welded are first machined (planed) to produce coplanar ends
that are then simultaneously pressed against the heating element.
The welding surfaces are heated by the heating element (hot plate)
and adapted under the adaption pressure. Thereafter, heating continues under reduced pressure (soak pressure) for the heating time
and, after removing the heating element, the ends are pressed together and the joint is formed under the welding pressure. Figure
6.28 provides a schematic representation of the butt welding process; heating temperatures are varied according to the wall thickness, Figure 6.27.
Figure 6.27 Heating temperature as a function of PE pipe wall
thickness
205
6CONSTRUCTION
Y o u r
V a l u e
P a r t n e r
Figure 6.28 The development of the process of butt welding
The execution of the butt welding
process is described in
SANS10268-1 - Heated tool
welding ISO/TC138 has also
composed working document
'ISO1307' to standardise the butt
welding process.
N/mm2
p1
p3
A
B
* SANS10268-1 - Heated tool
welding
p2
p
p4
t4
t3
t1
t2
t6
t5
(s)
t
Table 6.7 Explanation
Sign
de
e
A
B
p1
p2
p3
p4
t1
t2
t3
t4
t5
t6
Name
nominal outside diameter of pipe
minimum pipe wall thickness
bead size (end of adaption time)
bead size (end of cooling time under pressure)
pre-heating pressure
heating pressure
welding pressure
cooling pressure
pre-heating time
heating time
maximum conversion time
maximum built-up time
maximum welding time, under welding pressure
maximum cooling time, under cooling pressure
Entity
mm
mm
mm
mm
N/mm2
N/mm2
N/mm2
N/mm2
s
s
s
s
min
min
about (0.5 + 0.1 e) around even
minimum 3 + 0.5 e; maximum 5 + 0.75 e
0.18 +/- 0.01
almost no pressure, up to about 0.01 p3
0.18 +/- 0.01
0 (no pressure, without flexural and/or tensile stress)
until bead size A is reached
(12 +/- 1) e
3 + 0.01 de
3 + 0.03 de
3+e
1.5 e
Table 6.8 Process parameters for butt welding
de
mm
32
40
50
63
75
90
110
125
140
160
180
200
225
250
280
315
355
400
450
500
560
630
e
(SDR11)
mm
2.9
3.7
4.6
5.8
6.8
8.2
10.0
11.4
12.7
14.6
16.4
18.2
20.5
22.7
25.4
28.6
32.2
36.3
40.9
45.4
50.6
57.2
F1/F3*
A
Fd**
t2
t3
t4
t5
Bmin
Bmax
t6
kN
0.05
0.08
0.12
0.19
0.26
0.38
0.57
0.73
0.91
1.20
1.52
1.87
2.37
2.92
3.66
4.63
5.88
7.47
9.46
11.67
14.58
18.53
mm
0.8
0.9
1.0
1.1
1.2
1.3
1.5
1.6
1.8
2.0
2.1
2.3
2.6
2.8
3.0
3.4
3.7
4.1
4.6
5.0
5.6
6.2
kN
0.003
0.004
0.01
0.01
0.01
0.02
0.03
0.04
0.05
0.07
0.08
0.10
0.13
0.16
0.20
0.26
0.33
0.41
0.53
0.65
0.81
1.03
s
35
44
55
70
82
98
120
137
152
175
197
218
246
272
305
343
386
436
491
545
607
686
s
3
3
4
4
4
4
4
4
4
5
5
5
5
6
6
6
7
7
8
8
9
9
s
4
4
5
5
5
6
6
7
7
8
8
9
10
11
11
12
14
15
17
18
20
22
min
6
7
8
9
10
11
13
14
16
18
19
21
24
26
28
32
35
39
44
48
54
60
mm
4
5
5
6
6
7
8
9
9
10
11
12
13
14
16
17
19
21
23
26
28
32
mm
7
8
8
9
10
11
13
14
15
16
17
19
20
22
24
26
29
32
36
39
43
48
min
4
6
7
9
10
12
15
17
19
22
25
27
31
34
38
43
48
54
61
68
76
86
* at specific welding pressure of 0.18 N/mm2
** at specific welding pressure of 0.1 N/mm2
206
e
(SDR17)
mm
1.9
2.4
3.0
3.8
4.5
5.4
6.6
7.4
8.3
9.5
10.7
11.9
13.4
14.8
16.6
18.7
21.1
23.7
26.7
29.7
33.2
37.4
F1/F3*
A
Fd**
t2
t3
t4
t5
Bmin
Bmax
t6
kN
0.03
0.05
0.08
0.13
0.18
0.26
0.39
0.49
0.62
0.81
1.02
1.27
1.60
1.97
2.47
3.13
3.98
5.04
6.39
7.90
9.89
12.53
mm
0.7
0.7
0.8
0.9
1.0
1.0
1.2
1.2
1.3
1.5
1.6
1.7
1.8
2.0
2.2
2.4
2.6
2.9
3.2
3.5
3.8
4.2
kN
0.00
0.00
0.00
0.01
0.01
0.01
0.02
0.03
0.03
0.04
0.06
0.07
0.09
0.11
0.14
0.17
0.22
0.28
0.36
0.44
0.55
0.70
s
23
29
36
46
54
65
79
89
100
114
128
143
161
178
199
224
253
284
320
356
398
449
s
3
3
4
4
4
4
4
4
4
5
5
5
5
6
6
6
7
7
8
8
9
9
s
4
4
5
5
5
6
6
7
7
8
8
9
10
11
11
12
14
15
17
18
20
22
min
5
5
6
7
8
8
10
10
11
13
14
15
16
18
20
22
24
27
30
33
36
40
mm
4
4
5
5
5
6
6
7
7
8
8
9
10
10
11
12
14
15
16
18
20
22
mm
6
7
7
8
8
9
10
11
11
12
13
14
15
16
17
19
21
23
25
27
30
33
min
3
4
5
6
7
8
10
11
12
14
16
18
20
22
25
28
32
36
40
45
50
56
6CONSTRUCTION
Y o u r
Butt welding of PE pressure pipes involves
the following steps:
V a l u e
P a r t n e r
Heating
Both surfaces (ends) to be welded are pressed against the hot
plate under the welding pressure; the better the preparation, the
more even the weld bead formed. The pipe or fitting is held against
the hot plate until the welding bead has reached the prescribed
height and the heat saturation phase then follows.
Preparation
The following rules are important for the execution of a good butt
weld:
• The work site must be sheltered from the weather conditions.
• The operation of the butt welding equipment must be regularly checked; especially machines used on construction sites.
• The pipes or fittings to be welded must be aligned in the machine and clamped so that no misalignment of the walls, more than 10% of the wall thickness, exists.
• The pipe or fitting surfaces to be welded must be planed to make them coplanar and parallel to the hot plate so they can subsequently be evenly heated; planing also removes the oxidation layer on PE which may prevent a good butt weld from being produced.
• The prepared surfaces must be kept clean: welding surfaces must be free of oil, grease and dust.
• The hot plate must be regularly cleaned with a non-fraying paper and an appropriate, non-contaminating cleaning agent.
• The temperature of the hot plate must be between 200°C and 220°C, the higher temperature is used with smaller wall thicknesses; the maximum temperature deviations are shown in Table 6.9.
Figure 6.30 Heating a pipe or fitting
Heat saturation
During heat saturation (soak), the welding surfaces are held
against the hot plate under slight pressure (0.01 N/mm2) so heat
spreads evenly through the components to be welded as the weld
bead increases in height.
Figure 6.31 Heat saturating a pipe or fitting
Hot plate with electrical temperature control
Table 6.9 Maximum temperature deviations
Usable surface
up to 250 cm2
5°C
3°C
8°C
> 250 cm
7°C
3°C
10°C
2
= max. temperature difference within usable surface
= temperature difference over control interval
= +
= max. acceptable temperature deviation from setting
Preparing the welding surfaces
Surfaces are planed until they are coplanar and parallel to the hot
plate, see Figure 6.29.
Figure 6.29 Planing welding surfaces
Conversion
After heat saturation, the hot plate is removed and the welding surfaces pushed against each other as quickly as possible, without
impact, to avoid cooling of the surfaces to be fused.
Welding and cooling
The surfaces to be welded must be brought together as quickly
as possible after the heating and the welding pressure is applied
during the pressure build-up time in accordance with SANS 102681, the specific welding pressure for PE100 is P = 0.17 + 0.02 N/
mm2.
The build-up of welding pressure must occur evenly with a deviation of no more than 0.01 N/mm2.
If the pressure build-up is too rapid, it will cause the plastic material
to be pushed aside, if it is too slow, it will cause the material to cool
down too much; the weld quality will be affected in both cases.
207
6CONSTRUCTION
Y o u r
V a l u e
P a r t n e r
Figure 6.32 Welding/Cooling a pipe or fitting
Figure 6.34 Electrofusion
Cooling
Like butt welding, electrofusion is a widely-used welding technique in PE pipeline construction.
The welding pressure is maintained throughout the entire cooling
time with no mechanical load placed on the weld joint and the welding zone is prevented from cooling too quickly or abruptly. After
welding, an even double bead must have been formed and the
form of the bead will give a good visual initial indication of the quality of the weld joint, see SANS 10268-10. Sometimes, bead composition variation or irregular bead formation may not be an indication
of poor workmanship, but the different flow behaviours (viscosities)
of the molten plastics of the two components being welded that is
responsible; the bead size "K" must always be > 0.
Its applications have the following advantages:
• simple procedure throughout the entire welding process
• uncomplicated operation of the welding apparatus
• consistent welded joint quality due to reproducible equipment settings
• longitudinally rigid joint
• no weld bead inside pipeline
• welding is possible in hard-to-access locations
Figure 6.28 and Table 6.8 show standard values for the weld cycle,
however, the welding machine settings depend on the drag pressure required to overcome machine friction and component movement. The welding tables for the individual welding machine, plus
the drag pressure, must be used to set welding pressure.
6.4.2.3 Electrofusion
Description
The electrofusion coupling is used to connect pipe and fitting components in pressure pipe installations for gas and water supply
networks, industrial facilities and pressurised drainage systems;
the process is suitable for connecting pipeline components of the
series:
ISO-S pipe series number / SDR
- S 5 / SDR 11 (PE100)
- S 8 / SDR 17 (PE100)
Figure 6.33 Electrofusion coupling
Welding occurs in an overlapping format whereby the pipes and
fittings are joined together by an electrofusion coupling. The resistance coil (heating coil) integrated into the electrofusion coupling
is heated by an electrical welding unit, which causes the surface
of the component (outer) and the coupling (inner) immediately in
contact with the heating coil to be plasticised. The thermal expansion of the plastic creates the welding pressure so the effect of
these two parameters, heat and pressure, result in a homogeneous
connection between coupling and pipe or fitting at the end of the
welding process. SANS 10268-2 is applicable to electrofusion of
pressure pipe installations and makes recommendations for quality
assurance and available testing methods.
Electrofusion process
The execution of the electrofusion process is described in the
welding standard SANS 10268-2, Welding of thermoplastics –
Welding processes Part 2: Electrofusion welding.
Preparation
1. Inspect the pipe and fitting for damage and correct dimensions
2. Check the condition and operation of welding unit
3. Provide protective measures if weather conditions make it necessary
4. Pipes, fittings and welding equipment shall be kept at a constant ambient temperature between -10°C and + 45°C
5. Do not weld when medium is being discharged
208
6CONSTRUCTION
Y o u r
Figure 6.35 to 6.38 Pre-treatment
V a l u e
P a r t n e r
Figure 6.42 & 6.43 Positioning
Positioning
1. Push the pipe into the fitting up to the mark
2. Connect contact plugs to fitting: ensure tension-free assembly
• push pipe straight into coupling
• do not rotate
• coupling should be movable by hand
3. SANS 10268-2 prescribes the use of clamps for tension-free assembly
Pre-treatment
Figure 6.44 Clamps
1. Cut the pipe square
• slanting cuts may result in inadequate melting, overheating or burning
2. Clean the pipe
3. Mark the welding zone
4. Remove oxidation layer
• scrape off a long, even, continuous chip (min 0.15mm thick)
• an excessively thick chip will prevent the gap between coupling and pipe from being filled
• scraping 5mm extra in width is a sign of good workmanship
• filing or sanding is not permitted
5. Debur the pipe
6. Make oval pipe round, be careful with coiled pipes
• use rounding clamps if ovality >1.5% diam. or >1.5mm
Figure 6.39 to 6.41 Cleaning
Welding
1. Scan barcode with hand reader
2. Start welding process: electrofusion unit automatically regulates the amount of energy and welding time
• safe distance to welding location is 1m
3. Compare actual with required welding time
4. Note actual welding time on the pipe
• welding indicator provides an indication of the completed weld, correctness is also indicated by the welding unit
Figure 6.45 to 6.48 Welding
Cleaning
1. Mark the welding zone again
2. Clean the welding surface of the pipe
• welding surfaces must be absolutely clean
• use PE cleaning agent and absorbent, non-fraying, uncoloured paper
3. Clean inside of coupling
• take fitting out of packaging just before use
• prevent rubbing contaminants from untreated surfaces from entering the welding zone
Cooling
1.
2.
Adhere to the cooling time (CT) on the barcode before moving the connection
Cooling time prior to testing or operation pressure is indicated in the tables of the FRIALEN® assembly manual
Figure 6.49 Cooling
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6.4.3 Test Procedures for Evaluating Welds
V a l u e
P a r t n e r
Figure 6.51 Butt weld with identical welding beads (good)
Completed components are generally only tested by non-destructive test procedures. Destructive test methods are usually used in
cases involving damage claims or in the development of new materials and manufacturing procedures.
Figure 6.50 Test procedures used for plastic
Test procedures
Non-destructive-free
testing procedure
Destructive testing
procedures
Ultrasonic test
Tensile test
X-ray test
Impact tensile test
Spark induction test
Creep tensile test
Misalignment of the two ends may have various causes, uneven
narrowing of one of the ends or ovality, or both of these possibilities. Provided the difference is less than 10% of the pipe or fitting
wall thickness, the weld may be regarded as "acceptable", see Figure 6.52.
Figure 6.52 Butt welding with acceptable wall misalignment
Technologicalflexural
flexual
Technological
test
test
The most frequently used test in plastic pipe construction is visual
inspection, which involves an external visual evaluation of manufactured products, components and welds.
The visual inspection of butt welds can be performed without special tools if the tester has the appropriate knowledge and experience.
The extent of visual evaluation of electrofusions is limited, therefore, the checks concentrate on weld preparation and the implemented welding parameters.
If the temperature or the pressure is too high, it may cause the
beads to be too large. Figure 6.53 shows that the uniformity of the
two beads makes this weld still "acceptable".
Figure 6.53 Butt weld with welding beads that are too large but
still acceptable
The evaluation of welded joints in pressure systems and most used
welding techniques is described in SANS 6269.
6.4.3.1 Visual inspection of butt welds
Butt welds are primarily visually inspected; the evaluation of butt
welds is described in SANS 10268-10.
The bead must be of uniform shape, the weld area must be free of
tears, contamination or other damages and the dimensions of the
bead must match Table 6.8.
The bead form is an indication of the care with which the welding
process has been performed. Both beads shall be of the same form
and size, but differences between the beads may be caused by
differences in the flow characteristics of the surfaces being welded
together; the weld may still be functionally sound. Figure
6.51 shows a good weld with identical beads.
Figure 6.54 represents a weld with beads that are too small, suggesting that the temperature or pressure was too low. In thick walled
pipes, undersized beads are often associated with the formation of
shrinkage cavities; these types of welds are non-conforming.
Figure 6.54 Unacceptable butt weld
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Figure 6.55 shows the cross-sectional view of a good weld, the
bead is rounded, notch-free and with a misalignment of max. 0.1
"e". The bead size "K" shall be not less than the wall thickness "e".
Figure 6.55 Cross-section of a good weld
V a l u e
P a r t n e r
Visual inspection
Apart from the sample destructive testing, an accurate visual inspection is of crucial importance, together with the establishment
of welding parameters. The appearance of the actual welds must
be carefully examined and compared to the reference welds; no
significant deviations from the reference welds shall be allowed.
No scratches, impurities or other damage may appear in the welding zone.
6.4.3.2 Visual inspection of electrofusion
joints
An indication of weld quality based on the bead form in butt welding
cannot be obtained in the same way in electrofusion. An indication
of the plasticisation, and the associated weld between the electrofusion coupling and the adjacent components can only be done on
the basis of the indicators on the coupling. If they do not provide a
clear indication of the quality of the weld and the joint must not be
destroyed, one of the non-destructive testing procedures may be
employed, e.g. ultrasound or X-rays, which are generally expensive and too inaccurate to evaluate the weld quality. When visually
inspecting the weld, be absolutely certain that there is no visible
damage, e.g. scratches, tarnished surfaces and scoring in the vicinity of the coupling caused by the mechanical procedures used
during the welding process.
Attention shall further be paid to:
• proper insertion depth of the pipe in the fitting
• alignment of the various components in the pipe system
• deviation from the straight alignment of the pipe in the coupling shall not exceed 1mm deviation, 300mm from the socket (angle of deviation < 0.2°)
• resistance coil is not visible
• uniform filling of the gap between coupling and pipe
• heat damage
• bonding flaws due to bent pipes or distortion of saddles
• ovality of the pipe in the coupling after welding shall not be more than 1.5% of the average outside diameter of the pipe, with a maximum of 1.5mm
• the presence of welding indicators, if any
See Figure 6.56 and 6.57
Figure 6.56 Visual inspection of electrofusion joints
The following is a description of the evaluation of an electrofusion
weld from the standards:
An electrofusion weld is of good quality when the weld has sufficient mechanical strength over the long-term, and the welding
zone is homogeneous and free of cracks, contaminants and holes.
In addition, verification must be made of the correct welding and
cooling times used in the process. For proper quality control, it is
also necessary to make a few trial welds prior to the production
welding. These are performed under controlled work site conditions
using the applicable type of material and accurately observing the
welding conditions; heating and cooling times. A few of these welds
shall be subjected to destructive testing:
• on the basis of a tensile test
• on the basis of a detachment test
The test welds can be further used as reference material for visual
inspections of the actual welds.
All joints welded with non-conforming parameters, or in which the
welding does not meet stated requirements concerning their execution, are to be removed.
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Figure 6.57 Visual inspection of electrofusion joints
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6.5 JOINTING BY PRODUCT
Refer to Figure 6.58
Installation
16-63mm
Use a pipe cutter to cut pipe at 90° to its axis. Fig 1
Insert over the pipe end in the following order: nut, clinch ring and O-ring on the mouth of the pipe. Fig 2
Insert the pipe end and O-ring into the body of the joint; up to the insertion depth tab. Fig 3
Push the clinch ring into the body of the joint. Fig 4
Engage the nut and fully tighten. The nut can be tightened manually up to fittings of 32mm diameter. It is advisable to use a strap or plumbing wrench for larger diameter fittings. Fig 5 & 6
75-90mm
•
•
•
•
•
Insert over the pipe end in the following order: nut, clinch ring, thrust bushing and O-ring on the mouth of the pipe. Fig 7
Lubricate the pipe and the O-ring. Insert the pipe end and O-ring into the body of the joint; up to the insertion depth tab. Fig 8
Push the thrust bushing into the body of the joint. Slide the clinch ring up to the thrust bushing. Fig 9
Engage the nut and fully tighten with a strap or plumbing wrench. Fig 5 & 6
110mm
•
•
•
•
•
•
P a r t n e r
Figure 6.58 Installation of Marley Compression Fittings
6.5.1 Marley Compression Fittings
•
•
•
•
•
V a l u e
Insert over the pipe end in the following order: nut, thrust bushing and O-ring on the mouth of the pipe. Fig 10
Lubricate the pipe and the O-ring. Insert the pipe end and O-ring into the body of the joint; up to the insertion depth tab. Fig 11
Push the thrust bushing into the body of the joint and fasten the nut.
Unfasten the nut and slip the clinch ring over the pipe. Slide the clinch ring up to the thrust bushing. Fig 12
Engage the nut and fully tighten with a strap or plumbing wrench. Fig 5 & 6
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6.5.2 Magnum Saddles
Saddle Installation
Use
Can be used to fit a wide range of pipes, that have metric external
diameter dimensions. (including PVC, MDPE, HDPE, PP, or ABS)
Pre-assembly
Select branch off-take position, clean pipe, ensure easy access
and mark hole. Place saddle upper body and align outlet branch
with marked hole.
Assembly
Place saddle lower body over pipe. Ensure thread of bolts are
clean before placing in saddle. Tighten all bolts alternatively around
saddle. Ensure saddle off-take hole stays in alignment with marked
hole. Drill suitable sized hole through orifice of saddle with boring
tool. Ensure that the threads and gasket are not damaged.
Disassembly
Check that the pipes are free of cuts and abrasions (the maximum
depth allowed is equal to 10% of the wall thickness). Anomalies
must be removed by cutting the desired pipe section.
The pipe ends to be welded must be cut at a right angle using
proper pipe cutters. Avoid using ovalised pipes. Ovalisation cannot
exceed 1,5%, calculated as follows:
Equation 6.10
Figure 6.59 Scraping
Loosen and detach all bolts around saddle.
6.5.3 Butt welding / Electrofusion
Jointing Process
Electrofusion sockets and integrated fittings
The jointing quality directly depends on strict compliance with the
following instructions.
Scraping
Preparation
The jointing process must be carried out in a dry and protected
area. In case of adverse ambient conditions (humidity, rain, snow,
blast, excessive solar irradiance), suitable measures must be taken
to protect the working zone.
A critical element for jointing reliability is the preparation of the pipe
surface where the electrofusion fitting will be welded through the
removal of the oxidised layer, and the accurate cleaning of the
whole contact area with the fitting itself.
The above procedure refers to pipes, however the same procedure
can be equally applied if, instead of a pipe, a butt-fusion spigot
fitting is inserted.
1. 2. 3. 4. 5. 6. 7. Clean the pipe ends from dust, gum, grease and dirt. Mark the
scraping area with a marker pen or wax pencil, the pipe length
to be scraped must be 10mm larger than the electrofusion fitting
insertion depth. The electrofusion fitting MUST NOT be scraped.
Clean the surface of the pipe by scraping it. The operation must be
done using a scraper supplied with the control unit, or using a specialised mechanical pipe scraper. A uniform layer of material must
be removed for a depth of approximately 0,1mm for pipe diameters
up to 63mm, and approximately 0,2mm for diameters greater than
63mm. Using the scraper, consider the procedure as correct when
a uniform PE shaving is attached to the pipe end. Then remove it
by slightly rounding off at the pipe/fitting end at a 45° angle. AVOID
the use of sandpaper, rasp, emery wheels, saw blades or other
equipment.
Electrofusion fitting
Aligning clamp
Manual or mechanical scraper
Pipe cutter
Detergent
Cleaned cloth or strong soft paper
Marker pen or wax pencil
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This mark, besides assisting with the positioning of the fitting on the
pipe, will provide control at the welding end to ensure that there is
no movement of the jointing.
Figure 6.60 Cleaning
Insert the electrofusion fitting on
the end of the first pipe up to the
location mark. Fasten the pipe
into the aligning clamp.
Cleaning
Insert the second pipe into the
fitting up to its location mark and
fasten it into the aligning clamp.
Just before the jointing with the electrofusion fitting, clean all
scraped surfaces using a strong, soft paper slightly drenched with
a suitable detergent (i.e. isopropyl alcohol or methylene chloride)
to remove any trace of dust and grease. Do not use products such
as thrichloroethylene, cleaning alcohol, gasoline, acetone or paint
diluent.
Clean in the same way as the inner surface of the electrofusion
fitting, which must be removed from its protective wrapping only
at the moment of use. Do not touch the just-cleaned surfaces with
hands; on the contrary, repeat cleaning.
Figure 6.62 Welding
Figure 6.61 Positioning
Welding
Connect the plugs of the control unit to the terminals of the fitting
and proceed with the set-up of the welding parameters according
to the welding unit instructions.
Positioning
N.B.: If the welding cycle is accidently interrupted, the operation
can only be repeated after the electrofusion joint has been totally
cooled.
It is compulsory to make use of the aligning clamp, for all diameters to be welded, which:
•
•
•
removes the jointing stresses during the fusion of material and the subsequent cooling time;
allows you to revise possible off-centering
between the elements to be welded;
allows you to recover the out-of-round of parts, if ovalised.
When the fusion cycle is complete, verify the fusion indicators displayed.
WARNING: the fusion indicators do not guarantee the success of
the welding. This is exclusively an indication of the material fusion.
In order to set the aligning clamp to the different diameters, it is
necessary to insert the reducing inserts and adjust the internal distance between the movable jaws. In the case of electrofusion fitting
installations such as 90° and 45° elbows, suitable aligning clamps
are available with adjustable joints.
By using a coloured pen or wax pencil, mark the insertion depth on
at least one third of the pipe circumference, in correspondence with
the ends to be welded. This operation must also be carried out in
cases of fittings with a central stop.
Cooling
Generally, the cooling time of the joint can vary according to the
diameter and fitting type, from 10 up to 30 minutes as indicated
by the fitting manufacturer. During this time, the joint cannot be
moved or removed from the aligning clamp, or stressed. At fusion
cycle end, it is advisable to write, with a coloured pen or wax pencil,
the time that the jointing will be completely cooled. It is absolutely
forbidden to use external cooling methods (water, compressed air,
etc.) to speed up the cooling process. In any case, the pipeline
cannot be put into pressure for 2 hours from the last fitting being
welded. The welding parameters used for the jointing of each fitting
must be recorded in a proper report.
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6.5.4 Electrofusion Tapping & Spigot Saddles
V a l u e
P a r t n e r
Ovalisation and bending are reduced by using special re-rounders.
The coiled pipes must be unrolled at least 24 hours before use.
Avoid the use of a heat source to recover possible ovalisations or
to reduce pipe bending.
Electrofusion tapping and spigot saddles
Figure 6.64 Scraping
The jointing process must be carried out in a dry and protected
area. In case of adverse ambient conditions (humidity, rain, snow,
blast, excessive solar irradiance), suitable measures must be taken
to protect the working zone.
Preparation
A critical element for jointing reliability is the preparation of the pipe
surface where the electrofusion fitting will be welded through the
removal of the oxidised layer, and the accurate cleaning of the
whole contact area with the fitting itself.
Check and prepare all the materials necessary for the welding
process: - EF control unit
1. Upper saddle
2. Blank saddle
3. Bolts
4. Manual scraper
5. Detergent
6. Cleaned cloth or
strong, soft paper
7. Manual or pneumatic
screwdriver
8. Manual hexagonal key
for the cutter screw
9. Marker pen or wax pencil
Scraping
Clean the pipe ends from dust, grease and dirt. Mark the scraping
area with a marker pen or wax pencil.
Clean the surface layer by scraping the external pipe surface for at
least 10mm over the previous marked area. This must be done using the manual scraper supplied with the EF control unit. Remove
a uniform surface layer of material for a depth of approximately
0,1mm for diameters up to 63mm, and approximately 0,2mm for
diameters greater than 63mm. AVOID the use of abrasive paper,
rasp, emery wheels, saw blades or other equipment.
Figure 6.65 Cleaning
Figure 6.63 Preparation
Cleaning
Check that the pipes are free of cuts and abrasions (the maximum
depth allowed is equal to 10% of the wall thickness). Anomalies
must be removed by cutting the desired pipe section.
The pipe ends to be welded must be cut at a right angle using
proper pipe cutters. Avoid using ovalised pipes. Ovalisation cannot
exceed 1,5%, calculated as follows:
Equation 6.11
Just before positioning the saddle on the pipe, clean the scraped
surface with a clean cloth or strong, soft paper slightly drenched
with suitable detergent (i.e. isopropyl alcohol or methylene chloride) to remove any trace of dust and grease. Do not use products
such as thrichloroethylene, cleaning alcohol, gasoline, acetone or
paint diluent.
Clean in the same way as the inner surface of the upper saddle,
which must be removed from its protective wrapping only at the
moment of use.
Do not touch the just-cleaned surfaces with hands; on the contrary,
repeat cleaning.
Positioning the Saddle on the Pipe
Insert the hexagonal nuts in the seats on the blank saddle, and
the bolts complete with washers in the upper saddle. Position the
upper saddle on the pipe, centering it on the scraped surface.
Clamp the saddle on the pipe by tightening the four connection
bolts: proceed alternatively, in a criss-cross manner using a screwdriver or wrench according to the type of bolt. Proceed by tightening the bolts until the saddle is fully blocked on the pipe.
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Figure 6.66 Welding
Figure 6.68 Boring
Welding
Boring
Connect the plugs of the control unit to the terminals of the fitting
and proceed with the set-up of the welding parameters, strictly following the welding unit instructions.
The saddle boring must be carried out only after the welded joint is
completely cooled, independently from the type of saddle, and not
20 minutes before the cooling time indicated on the fitting.
N.B.: If the welding cycle is accidently interrupted, the operation
can only be repeated after the electrofusion joint has been totally
cooled. When the fusion cycle is complete, verify the fusion indicators displayed.
code 21.30: ef tapping saddle
WARNING: The fusion indicators do not guarantee the success of
the welding. This is exclusively an indication of the material fusion.
Figure 6.67 Cooling
Unscrew the outlet cap of the saddle. Insert the manual hexagonal
key into the built-in cutter. Avoid the use of pneumatic or electric
screwers, which due to the excessive rotation speed, can damage
the cutter thread. Screw clockwise until the pipe perforation, this is
evidenced by a great decrease in the screwing force. Do not continue in order to avoid any damage to the cutter thread.
Screw anti-clockwise and retract the cutter back to its original position. Remove the hexagonal key and firmly screw the cap, checking the presence of the internal O-ring gasket.
Cooling
The cooling time of the joint is always indicated by the fitting manufacturer. During this time, the joint cannot be moved or stressed. At
fusion cycle end, it is advisable to write, with a coloured pen or wax
pencil, the time that the jointing will be completely cooled.
Do not use external cooling methods (water, compressed air, etc.)
to speed up the cooling process. In any case, the pipeline cannot
be put into pressure for 2 hours from the last fitting being welded.
The welding parameters used for the jointing of each fitting must
be recorded.
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6.5.5 Butt Weld Process
V a l u e
P a r t n e r
Figure 6.70 Phase 1: Hauling & Pre-heating
Welding cycle at single pressure
The welding operations must immediately follow the ends preparation phase. On trench site, if within the time between the planing
phase and the welding starting operation, dust traces, grease or
dirt are settled on the ends to be welded, it is necessary to repeat
the cleaning process.
Figure 6.69 Welding cycle at single pressure
Phase 2
Heating
In a relatively short time, it forms a melted plastic ring which shows
that the material fusion process has started. At this step, the pressure at the point of contact of the ends with the heating plate must
be released, avoiding the push-out of the PE material from the
welding zone, which is necessary for a good quality jointing obtaining only a “cold” welding, which is extremely fragile.
Pressure is then released to its initial value P1 + Pt (Phase 1) up to
a P2 value which guarantees the ends contact and the heating plate
during the whole heating time and which satisfies:
Equation 6.13
P2 ≤ 0,02 N/mm2
Phase 1
Hauling and Pre-heating
The two surfaces to be welded are put in contact with the heating plate, taking care to insert it correctly in order to guarantee its
steadiness. Afterwards, draw both ends close to the heating plate
and apply the pressure: P1 + Pt
Where P1 is deduced from the tables supplied by the machine manufacturer and then summed to the drag pressure Pt. The pre-heating phase ends after a time (t1) is sufficient as long as it forms a
ring of fused material on both welding ends in which the width is
equal to:
Whenever P2 is not specified in the table supplied with the machine, in the operative practice it is advisable to set the pressure
gauge on a value next to zero but never higher than Pt. If the operation is correct, the surface heating continues without increasing the
overthickness of the ring. In this phase, the ends must be in contact
with the heating plate for a time equal to:
Equation 6.14
t2 = 12 × en [seconds]
Where en is the nominal thickness of the pipe and/or fitting to be
welded. A tolerance of (+8%, -0%) is admitted on the t2 value.
Figure 6.71 Phase 2: Heating
Equation 6.12
A = 0,5 + (0,1 x en) [millimetres]
welded.
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Phase 3
V a l u e
P a r t n e r
Figure 6.73 Phase 4: Build-up welding pressure
Removal of the heating plate
At the end of the time (t2), the ends are separated to allow the heating plate to be removed (take care to avoid damage to the ends to
be welded) and then brought together for jointing. This phase is
extremely critical and its correct performance is essential for successful welding. The removal of the heating plate has to be as fast
as possible in order to avoid the excessive cooling of the ends; at
the same time, it is necessary to reduce the closing speed for putting the two ends into contact, in order to obtain a jointing that does
not result in the abrupt extrusion of the melted material.
This allows the two parts to correctly melt and avoid the formation
of cold areas inside the joint. The entire operation must be completed within a time shorter than:
Equation 6.15
Phase 5
Welding
Keep the ends in contact with pressure (P5 + Pt) for a time equal
to:
Equation 6.17
t5 = 3 + en [minutes]
t3 = 4 + (0,3 × en) [seconds]
welded. A tolerance of (+10%, -0%) is admitted on the t5 value.
welded.
Figure 6.74 Phase 5: Welding
Figure 6.72 Phase 3: Removal of heating plate
Phase 6
Phase 4
Cooling
Build-up welding pressure
Put the ends into contact by increasing pressure in a progressive
way and to avoid a harsh and excessive extrusion of the melted
material from both surfaces, up to the value of: P5 + Pt
Where P5 (equal to P1) is deducted from the tables supplied by the
machine manufacturer and then summed to the drag pressure Pt.
The reaching of this pressure must be within a time equal to:
At the end of the time (t5), the pressure is released to zero and the
welded joint can be removed from the clamps. The joint must not
be stressed until it is cool to the touch, as it may form cracks and
slackenings in the cut area. The cooling must be carried out naturally, avoiding quick cooling methods such as water, compressed
air, etc.
The cooling time must not be shorter than:
Equation 6.18
Equation 6.16
t6 = 1,5 × en [minutes]
t4 = 4 + (0,4 × en) [seconds]
welded.
welded.
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6.6 CUSTOMISED PRODUCT: WEHOLITE
PIPE HANDLING
6.6.1 Handling and Storage Instructions
V a l u e
P a r t n e r
Adequate level space must be reserved for unloading. Secure the
truck on level ground as well. The unloading equipment must be
capable of safely lifting and moving the pipe, fittings, fabrications,
etc.
Off-loading may be done by means of skid timber and strap slings
or with mechanical lifting devices. However, lifting chains, ropes or
hooks may not be used, as these may result in permanent damage to the product. Lifting points must be well spread and evenly
spaced.
Relevant national or local regulations must be observed.
6.6.1.1 General
Weholite pipes are sturdy and lightweight, which makes them easy
to use. Unfortunately, these properties also increase the temptation
to abuse the pipe. Proper handling is required to minimise the risk
of damage.
Figure 6.75 Off-loading pipes
Pipes must be handled with sufficient care. They can be damaged
if dropped or thrown about. Pipes or bundles of pipes must never
be dragged – the pipe surface may be weakened by scratches.
When transporting and storing pipes, care must be taken not to
permanently deform the pipes. Socketed pipes in particular must
be stored in such a way that their sockets are not subjected to
loading that will cause deformation.
6.6.1.2 Transport and unloading
Pipes should be transported on flat transport beds without sharp
edges or other projections that might damage the pipes. Movement or rubbing of pipes during transport must be prevented, for instance, by strapping the pipes down. When pipes of different sizes
are transported, the heaviest lengths are loaded underneath. If the
pipes are transported nested inside one another, the smaller pipes
are removed first and piled separately.
Upon arrival at the site, the pipe shipments are visually inspected
and checked against the packing list for correctness in size, stiffness and quantity.
The pipes must also be inspected for damage which may have
occurred during handling and/or transport. Obvious damage such
as cuts, abrasions, scrapes, tears and punctures must be carefully
inspected and noted. Any damage, missing items, etc. must be noted on the bill of loading and signed by the customer and the driver.
Shipping problems such as the above should be reported to the
supplier immediately.
6.6.1.4 Single pipes
When lifting single pipes, use pliable straps or slings. Do not use
steel cables or chains to lift or transport the pipe. Pipe sections
can be lifted with only one support point but, especially for larger
diameters, it is recommended to use two support points to make
the pipe easier to control. Do not lift the pipes by passing a rope
through the centre of the pipe end to end.
6.6.1.5 Nested pipes
Always lift the nested bundle by at least two pliable straps. Ensure
that the lifting slings have sufficient capacity for the bundle weight.
Stacking of nested pipes is not advised unless otherwise specified.
Figure 6.76 Correct loading & unloading
6.6.1.3 Correct loading and unloading
It is important that loading, unloading and handling be performed
safely to avoid damage to property or equipment. As loading and
handling can be a hazard to persons in the unloading area, unauthorised persons should be kept at a safe distance while unloading.
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6.6.2 Storage
V a l u e
Figure 6.77 Preferred lifting technique
Inspect all materials carefully upon arrival on site and note and
report any defects immediately. All pipe stacks must be made on
firm, flat ground that can support the weight of the pipes and lifting equipment. For safety and convenience of handling, the stack
height for pipes is limited to five units or not more than 2.8m. Stacks
must be adequately wedged to prevent movement.
Pipes must be stored on intermediate supports spaced not more
than 2m apart. The support width must be greater than the profile
width of the pipe size in question, but not less than 100mm. Pipes
with integral sockets must be stacked with the sockets at alternate
ends, or at least without loading the sockets. Pipes with z-cut ends
must be stored with the z-cut oriented in the same position (at 12
o’clock). The maximum storage height for pipe stacks is 2.8m overall.
Besides protecting all material adequately against theft, vandalism,
accidental damage or contamination, also keep pipes and fittings
away from sources of heat if at all possible. If the pipes are to
be stored for long periods, they must be protected against excessive heat; storage at high temperatures for prolonged periods can
cause excessive deformation that may affect installation.
Figure 6.78 Normal stacking of plain ended pipes
To avoid this risk, the following precautions are recommended:
a. Shield the stacks against continuous and direct sunlight and allow free passage of air around the pipes;
b. store the fittings in boxes, sacks or shading manufactured so as to permit free passage of air;
c. protect elastomer sealing rings against direct sunlight.
Figure 6.79 Stacking of socketed pipes
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P a r t n e r
6.6.3 Weholite Jointing
6.6.3.1 Socket jointing (Elastomer Sealing
Ring Joints)
The integral socket joint can be delivered as sandtight or watertight
(with rubber seal). The rubber seal conforms to international standards and is resistant to normal sewage waters. Seals resistant to
oil contaminated water are available upon special request.
Jointing must always be carried out in accordance with sound civil
practice. However, in the absence of instructions the following is
recommended:
a.
b.
c.
d.
e.
f.
Chamfer and deburr the spigot end when the sealing ring is in position in the socket.
Use only sealing rings and lubricants supplied or approved by the manufacturer of the pipe or fitting.
Ensure that cuts made on site are square. If necessary, set up a proper cutting zone. After cutting, chamfer or deburr the end to produce a finish equivalent to that of the pipe supplied by the manufacturer. Open profile closure needs to be repaired in pipes that will be air tested.
Clean the pipe end, the socket and the sealing ring groove, removing any foreign matter, water, sand, dirt, etc. Make sure the sealing ring sits correctly in its location.
Apply lubricant over the whole chamfered end, in the socket area or on the fixed sealing ring, as appropriate.
Carefully align the spigot with the adjoining socket and push to the required insertion depth (depth of entry mark). If a lever is used on the pipe to push the joint, insert a block of wood between the lever and the end of the pipe to prevent damage to the pipe.
2.Make sure that spigot end, socket and sealing ring are free from sand, moisture, dust, etc
Figure 6.80 Socket jointing
3.Install the rubber sealing ring in the groove. Make sure the tension in the rubber material is distributed evenly by applying force to the rubber ring.
1. Align the pipes vertically and horizontally
4.Apply lubricant evenly onto the spigot end and the rubber sealing.
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Special fittings for this purpose are available and must be fitted
in accordance with the manufacturer’s instructions (short length
double-socketed pipe).
6.6.3.5 Repairs
LP couplers or purpose-designed fittings are available for effecting
repairs. It is recommended that the following general points should
all be adopted, where applicable:
5.Gently push the spigot onto the socket using adequate force until the stop mark (depth of entry mark) made on site is at the socket opening. Use a plate or plank to avoid damage to the spigot or socket. Large dimensions may be installed by using an excavator. Protect the socket opening with a sheet or plank. Check that the sealing ring stays in position.
6.6.3.2 Welded joints
Welded and fused joints should always be made by qualified personnel and in accordance with the manufacturer’s instructions and
national standards.Extrusion welding is used for gravity applications where the joints must have full watertightness and tensile
strength, as well as 100% resistance to root encrease. Welding will
be undertaken by specially trained operators either from the inside
or the outside of the pipe, or both.
• The full extent of the damaged or failed section must be identified and removed.
• The cut pipe ends should be square and prepared for push-fit jointing.
• LP repair couplings should be placed in position on the exposed pipeline ends. The replacement pipe length should then be laid on the suitably prepared bed and the LP
couplings moved into their final positions.
• Ensure that the bedding does not interfere with the couplings and that the pipe ends are clean.
• Pull the couplings over the joint so that they are centrally located over the joints.
• Check the line and level of the newly installed pipe.
• Tighten all bolt tensioners evenly so that all the slack is taken up before tightening to coupler manufacturer's maximum torque requirements.
• The embedment should then be replaced to give compaction values approximately equal to those immediately adjacent to the repair.
• Prior to completing the backfill of the pipe, the bolts must be retensioned. Ideally, LP couplings should be retensioned on the morning after the repair has been carried out.
Figure 6.81 Wall passings / repairs
6.6.3.3 Connection to existing pipes
Weholite pipelines can be connected to existing pipelines or to
structured wall pipelines of a different design in a way similar to
a repair (see Repairs) by using an appropriate fitting. For saddle
connections, follow the saddle manufacturer’s instructions.
6.6.3.4 Connection to rigid structures
A structure may be a wall of a building, an inspection hole, other
pipelines, fittings such as valves or the like.
The connection of a Weholite pipe to a structure depends on the
pipe size as well as on the structure at the connection point. Connections must be made in such a way that the joint is tight and that
no damage is done to the pipe.
If a Weholite pipe is connected to a structure that may settle differently than the pipe, a flexible connection beneath the pipe in the vicinity of the structure must be used, or a transition zone permitting
pipe movement, or a strengthening construction.
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6.6.3.6 Threaded joints*
1.
2.
3.
4.
5.
V a l u e
P a r t n e r
3
Align the pipes vertically and horizontally.
Make sure that the threads are free from sand, moisture, dust, etc.
Thread the male end into the female end.
The pipes can be rotated using a lever or band-sling.
If necessary, an excavator can be used to help rotate the pipes. To facilitate the rotation, the pipes can be laid on planks or roller supports.
The joint as such is sandtight. If watertightness is required, the
joint can be extrusion welded from the inside (NS>800mm), from
the outside, or both. The joint can also be waterproofed using an
external shrink sleeve or rubber sleeve.
*Threaded joints subject to availability.
4
Figure 6.82 Threaded joints
1
5
2
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6.6.3.7 Rubber-sleeve joints
P a r t n e r
The largest permitted angular deflection in the elastomer ring seal
joint (the design angle) is
Rubber-sleeve LP couplings are designed for jointing pipes in
stormwater and other types of non-pressure applications in the
construction, repair and maintenance of pipelines. These include:
• Non-watertight jointing
• As a joint for plain-ended pipes
• Repair of existing pipelines
• As an adapter between pipes of different sizes or materials
6.6.3.8 Process: Rubber-sleeve joints
a.
b.
c.
d.
e.
V a l u e
Ensure that the bedding will not interfere with the couplings and that the pipe ends are clean.
Pull the coupling over the joint so that it is centred.
Check the alignment and level of the newly installed pipe.
Tighten all bolt tensioners evenly so that all the slack is taken up before tightening fully to 45Nm or refer to the sticker.
The embedment should then be replaced to give compaction values approximately equal to those immediately adjacent to the repair.
Equation 6.19
2° for de< 315mm
1.5° for 315 ≤ de ≤ 630
1° for de> 630
Large angular deflections are permitted in the case of joints specifically designed to accommodate such deflections. The manufacturer of the coupling will specify the permitted angular deflection.
Figure 6.84 Weholite LP Coupling Jointing Process
Prior to completing the backfill of the pipe, retension the bolts. Ideally, LP couplings should be retensioned on the morning after the
repair has been carried out.
Figure 6.83 Cross-section through sealing strip
1
5
2
6
3
7
4
8
6.6.3.9 Deviation from straightness
It is normal practice in sewerage and drainage that pipes are installed in straight lines. However, as Weholite pipes are longitudinally flexible, it is possible to bend them if required during the
installation. In such cases, minor misalignments of the pipeline can
be accommodated in the pipe itself by bending. The minimum permissible bending radius for Weholite pipes under normal installation conditions = 50 * De (outside diameter). There may not be any
bending at the socket. An acceptable bending radius can be maintained by lateral supports against the side of the trench. Special
care should be taken when bending pipes at low temperatures, and
the joint must be protected against any extra stress.
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6.6.4 Installation Types and Related Consolidation Deformation
V a l u e
P a r t n e r
Figure 6.86 Contribution Parametres
6.6.4.1 Design graph
An intensive study of the deflection history of pipes installed under
different conditions is presented in the graph.
Note: The average deflections immediately after installation are
represented by the lower boundary of each area, and the maximum
values by the upper.
Figure 6.85 Pipe deflection after installation
6.6.4.2 Validity of the design graph
The design graph is valid under the following conditions:
• Depth between 0.8m and 6m, both included.
• Depth/diameter ratio at least above 2.0.
• Designers first need to establish permissible deflections, average and maximum (national requirements product standards, etc.).
• Pipes fulfil the requirements listed in the Weholite internal standard and international standards.
• Installation categories “well”, “moderate” and “none” reflect the workmanship on which the designer can rely.
• Sheet piles are removed before compaction. If the sheet piles are removed after compaction, the “well” or “moderate” compaction level will be reduced to the “none” compaction level.
• For the deflection mentioned in the graph, the strain will be far below the design limit and need not be considered in the design.
“Well” compaction, Cf=1.0
The embedment soil of a granular type is placed carefully in the
haunching zone and compacted, followed by placing the soil in
layers of 300mm maximum, after which each layer is compacted
carefully. A layer of at least 150mm must cover the pipe. The trench
is further filled with soil of any type and compacted. Typical values
for the Proctor density are above 94%.
“Moderate” compaction, Cf=2.0
The embedment soil of a granular type is placed in layers of 500mm
maximum, after which each layer is compacted carefully. A layer of
at least 150mm must cover the pipe. The trench is further filled
with soil of any type and compacted. Typical values for the Proctor
density are in the range of 87-94%.
“None” compaction in granular soil, Cf=3.0
The embedment soil of a granular type is added without compaction. Installation of this type is NOT recommended.
“None” compaction in clay, Cf=4.0
Trench Work
The size and shape of the trench are planned on the basis of the
size of the pipe or pipes to be laid as well as the soil data gained
from soil investigations. The trench is generally made as narrow
as possible, taking into account the width needed for possible supporting structures, working space and space needed for proper
placement of the backfill soil. The minimum width of the bottom of
an open trench is 0.7m and that of a supported trench 1.0m. Making a trench unnecessarily wide should be avoided, as the effect of
the side support might be weakened.
When determining the trench depth, sufficient space for a bedding
layer of at least 150mm must be taken into account, should the
native soil be suitable as bedding. The final excavation is made
carefully, so that the bottom of the trench is kept as undisturbed as
possible. Moving about on a soft or easily disturbed trench bottom
must be kept to a minimum.
The slope of a trench wall and the need for support are determined
on the basis of appropriate needs and general workplace safety
aspects. The slope inclination and need for support are specified
in the national standard specification for civil engineering construction.
The embedment soil of a cohesive type is added without compaction. Installation of this type is NOT recommended.
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Bedding
On the bottom of the trench, on top of an exchange material or on
top of a grating, a 150mm-300mm thick bedding layer is prepared
and well compacted (>95% Proctor). The bedding may consist of
sand, gravel or crushed pebbles, free from stones within the width
of the pipe trench. The bedding needs to be at least 200mm wider
than the pipe outside diameter to enable proper compaction work.
For installations in wet or soft soil, a geotextile must be placed under the bedding in order to prevent the bedding from being washed
away.
The largest permissible particle size dmax for natural stone materials
to be used is determined on the outside diameter of the pipe to be
installed. For DN<600, dmax = 0,1 • DN. For DN>600, dmax is always
60mm. Crushed pebble material must not be larger than 32mm
and/or in accordance with national standards.
If a pipeline is founded directly onto levelled native soil, the trenching work must be done carefully, avoiding unnecessary over-excavation, in order to keep the trench bottom sufficiently level. The
whole bedding layer depth must be stone free.
V a l u e
P a r t n e r
The final layer of the primary backfill must extend 300mm above
the crown of the pipe; to avoid ovalisation of the pipe, the soil layer
on top of the pipe can only be mechanically compacted when it is
at least 300mm thick.
The degree of compaction must be at least 90-95% Proctor, if not
otherwise stated in the contractor’s plan. When removing supporting structures (such as sheet piles or trench boxes), take care not
to endanger work safety or trench wall stability, loosen the compacted backfill or move the pipe out of position.
The final backfill material may be compactable as-dug material, but
must in any case be free from stones larger than 300mm. Where
necessary, and especially in traffic areas, compaction is carried
out in several 300mm layers to compaction levels corresponding
to those of the primary backfill. On the surface, use backfill material
that matches the surrounding surface.
Figure 6.87 Backfilling
Laying
Before starting to lay the pipe, check that the pipes and materials to
be used are free from defects. Clean them carefully after transportation and any machining done before installation.
The pipes are laid on the levelled trench bottom or bedding so that
the pipe is supported evenly over its full length. Excavations are
made in the trench bottom or bedding for the sockets so that the
weight of the pipes does not rest on the sockets. Do not lay pipes
on top of wooden planks or similar.
During laying, the water level in the trench must be kept sufficiently
low to prevent flotation or water from damaging the laid pipe. When
laying work is interrupted, the ends of the pipes must be sealed to
prevent ingress of dirt or water.
When laying pipes in road and railway areas, instructions from the
relevant authorities must be observed.
Backfilling
The term “primary” refers to the material to be used around the
pipe above the native soil trench bottom or the bedding. Primary
backfill extends to at least 300mm above the pipe crown and/or as
specified by local standards.
6.6.4.3 Structural design
In general, structural design of a pipeline by analytical or numerical
methods is not needed. Any calculated prediction of the pipe behaviour depends greatly on the degree of correspondence between
the calculation assumptions and the actual installation; it is therefore important to base the former on reliable input values obtained
from extensive soil surveys and monitoring of the installation.
However, when structural design is required, e.g. in cases where
no other information exists, a method as defined in EN 1295-1
should be used. As far as input values for the pipes are required,
the following values are recommended:
Table 6.10 Input values
The primary backfill material must meet the same requirements
as the bedding materials. Backfilling should extend over the entire
trench width. The primary backfill material may not be dropped on
top of the pipe in such a way that the pipe is moved or damaged; it
must be placed as evenly as possible on both sides of the pipe and
packed under the pipe haunches and on the sides.
In the first stage, the material is spread in the trench with a spade
or by other means and compacted so that the pipe is not moved or
damaged. If necessary, the pipe may be pressed down or anchored
or filled with water to prevent it from lifting during compaction. The
backfill material is compacted in layers of 150-300mm.
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Material
PE
Remarks
E-modulus (MPa)
1000
Modulus of elasticity
(-)
0.4
Poisson's ratio
(mm/mm.K)
13 x 10-5
Lin. expansion coefficient
6CONSTRUCTION
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6.6.5 Pressure Testing on
Non-pressure Pipes on Site
In the acceptance inspection, if required, compliance of the installation work with the planning documents is verified. As part of the
final inspection, tightness can be tested. Tightness testing of
Weholite pipes is performed with reference to national requirements, but normally according to the following alternative methods:
SABS 2001 DP4 Standard specification for civil engineering construction; DP4 sewers SFS 3113. Leak testing on pipelines is conducted either with air or water.
6.6.5.2 Principle
(Summary of the Finnish standards SFS 3113) A delimited section
of pipe is filled with water and subjected to a certain overpressure.
The tightness is determined in the final stage of the test by determining the quantity of additional water needed to maintain the
pressure.
a.
b.
c.
The value thus obtained and the inside diameter of the pipe are
inserted in the diagram below. All readings below the line are acceptable.
For further information, see Standard SFS 3113.
Table 6.11 Test overpressure values
Graph 6.13 Overpressure in pipes
l/m h
2,6
2,2
2,0
1,8
1,6
1,4
1,2
1,0
duration of the test
Volume of the added water per length unit and the
2,4
0,8
0,6
0,4
0,2
0
600
800
1 000
1 200
1 400
Fill a pipe section with water to overpressure P. Check that all seals are watertight and hold the pressure for 10 minutes.
The overpressure is maintained at the level P during half an hour by adding water when necessary. Measure the volume of water added during three 6-minute intervals.
When the test is completed, the average volume of the added water is calculated. This volume is converted into functions of pipe length and time (ℓ/mh),
ℓ = litre of added water
m = length of piping in metres
h = hour
The necessary overpressure in the pipe depends on the level of
the ground water in relation to the level of the piping to be tested.
The difference between these two levels is marked with “a”. The
overpressure is derived from the following graph:
400
P a r t n e r
Method
6.6.5.1 Testing
200
V a l u e
1 600
Inside diameter mm
228
Test overpressure Pe1
Difference between the subsoil water and the pipe (m)
kPa
a<0
10.0
0.1
0<a<5
15.5
0.155
0.5<a<1.0
21.0
0.21
1.0<a<1.5
26.5
0.265
1.5<a<2.0
32.0
0.32
2.0<a<2.5
37.5
0.375
2.5<a<3.0
48.5
0.485
3.0<a<3.5
54.0
0.540
3.5<a<4.0
59.5
0.60
4.5<a<5.0
65.5
0.65
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6.6.6 General
All acceptance tests shall be carried out in the presence of the
engineer and at such times and in such manner as the engineer
may direct. Subject to the provision of 7.1.5, no pipe joint or fitting
shall be covered until the applicable tests given in 7.2 have been
completed and the engineer has:
a. given his written acknowledgement that the sewer or the specified section of it has passed the said test, and
b. authorised such covering.
The sewer or any section of it shall be inspected by the contractor
who, if he deems it ready to be tested, shall advise the engineer of
his intention to subject the sewer or said section of it to the appropriate tests.
The sewer shall be tested in sections between manholes or chambers, as applicable, the section being tested must be isolated from
other sections by means of suitable plugs or stoppers that have
been braced adequately.
Notwithstanding any acknowledgement by the engineer in terms of
7.1.2, after backfilling and compaction have been completed, the
engineer may order that the sewer be retested to check that it has
not been disturbed or damaged during backfilling.
The engineer may order one of the following to be carried out on
the sewer or any section of it:
a. 1. an air test on pipes (other than concrete pipes) of all sizes; or
2. in the case of pipes (other than concrete) of diameter up to 600mm, an air test followed by a water test;
b. a water test in the case of pipes of diameter up to 750mm;
c. a visual internal inspection in the case of pipes of diameter greater than 750mm.
The contractor shall provide all labour and apparatus (including expansive plugs and flexible bag stoppers) that may be required for
carrying out the tests.
All test results shall be recorded in the manner directed, whether or
not the pipeline or section of pipeline has passed the test.
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6.6.7 Tests and Acceptance/Rejection Criteria
V a l u e
P a r t n e r
The amount lost shall not exceed the applicable of the following
rates per 100m of pipeline per hour:
6.6.7.1 Air test
Table 6.13 Water test rates
Pipelines above the water table:
An approved air testing machine shall be used to raise the gauge
pressure in the section of the pipeline under test first to 3.75 kPa.
After a 2 min stabilisation period, the pressure shall be reduced
to 2.5 kPa. The machine shall then be switched off, and the time
taken for the pressure to drop from 2.5 kPa to 1.25 kPa shall be
determined. The time taken shall be at least the applicable of the
following values:
Table 6.12 Air test values
Nominal diameter of pipe (mm)
Minimum time (min) taken for pressure to
drop from 2.5 kPa to 1.25 kPa
100
2.0
150
3.0
200
4.0
225
4.2
250
4.5
300
6.0
375
7.5
450
9.0
600
12.0
750
15.0
Nominal diameter of pipe (mm)
Minimum time (min) taken for pressure to drop from 2.5
kPa to 1.25 kPa
100
6.0
150
9.0
200
12.0
225
13.5
250
15.0
300
18.0
375
22.5
450
27.0
600
36.0
750
45.0
Should any section of the pipeline fail to pass the water test, a retest will be permitted and, in such case, acceptance or rejection of
the section shall be determined on the result of the re-test.
6.6.7.3 Rejection
In the case of AC, vitrified clay and pitch-impregnated fibre pipes,
failure under the air test will be deemed to be cause for rejection.
After such rejection, the contractor may apply a water test to locate
the source of failure, rectify the pipeline, and re-apply the air test.
In the case of reinforced concrete, failure under the water test will
be deemed to be cause for rejection.
Pipelines below the water table:
6.6.7.4 Test of connecting sewers
An approved air testing machine shall be used to raise the gauge
pressure in the section of the pipeline under test to 2.5 kPa above
the static water pressure. After this pressure has been attained
and the machine stopped, any change in pressure shall be noted.
There shall be no discernible loss for a period of at least 5 min.
Each connecting sewer shall be tested between its upper end and
the junction at the main sewer. The upper end of the connection
shall be kept securely closed with expanding plugs during the test.
Where practicable, the contractor may test the main and connections simultaneously if he so wishes. On completion of the test,
the upper end of the connection shall be permanently sealed as
directed by means of a plug stopper suitable for the type of pipe.
6.6.7.2 Water test
The section of the pipeline under test and, unless otherwise specified, the manhole chamber at the upper end of the said section
shall be filled with water to such a depth that every portion of the
pipeline is subjected to a pressure of not less than 12 kPa and not
more than 60 kPa.
6.6.7.5 Test of rising mains
During the test, there shall be no discernible leakage of water. An
appropriate period, which shall be at least 10 min, shall be allowed
for initial absorption, and the loss of water over the next 30 min
shall be noted.
6.6.8 Support Spacing
After a rising main has been laid and the joints completed, the main
shall be slowly charged with water so that all air is expelled, and
then tested in accordance with Subclause 7.3 of SABS 1200 L.
Where so required in terms of the project specification, manholes
shall be tested for watertightness separately from the pipeline.
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6.6.8 Support Spacing
With installations above ground, the maximum support spacing can
be determined according to the figure on the left hand side.
Graph 6.14 Support spacing
Support spacing
- sag 10 mm/10 years
- liquid density 1 000 kg/m3
5
+ 20 °C
4
+ 40 °C
3
+ 60 °C
2
1400
1200
1000
800
600
400
200
1
0
Support spacing, m
6
Pipe ID, mm
6.6.9 Buoyancy
When installing pipes under the ground-water level, the buoyancy of the pipe must be taken into consideration. Where necessary, the
natural uplift of the pipe should be counteracted. This can be designed case by case. Please do not hesitate to contact your nearest
Marley branch for technical information.
Table 6.14 Buoyancy
DN/ID
mm
dn
mm
Pipe Empty
Profile Empty
kN/m
Pipe Full
Profile Empty
kN/m
Pipe Full
Profile Full
N/m
360
400
1.23
0.24
10
400
450
1.52
0.29
10
500
560
2.38
0.45
10
600
675
3.43
0.65
10
700
790
4.66
0.89
20
800
900
6.09
1.16
20
1000
1125
8.97
1.27
30
1200
1350
13.70
2.61
40
1400
1575
18.65
3.55
50
1500
1680
21.41
4.08
60
1600
1792
24.36
4.64
70
1800
2016
30.83
5.87
90
2000
2240
38.06
7.25
110
2200
2464
46.04
8.78
130
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6.7 CUSTOMISED PRODUCT: PETROPLAS
V a l u e
P a r t n e r
Figure 6.89 Storage of pipe coils
6.7.1 Storage and Materials Handling
The Petroplas product range is resilient, lightweight and easy to
handle, however care should be taken so as to avoid personal
injury or product damage prior to installation. Installers are also
required to familiarise themselves with the product, and the safety
and chemical data sheets for any cleaning solvents used.
6.7.1.1 Storage – Pipe
•
•
•
•
•
•
•
Keep protective packaging intact until the Petroplas pipe is ready for use.
Petroplas pipe should be stored away from direct sunlight. For an extended storage period (more than 3 months), Petroplas pipe should be completely covered with an opaque UV resistant material.
Keep Petroplas pipe away from excessive heat.
The storage area must be flat and level, with no sharp objects or projections and able to support the complete plan area and weight of the pipe being stored.
Pipe sticks should be stored in a bundled beehive
configuration not exceeding 915mm in height. See dimension A in Figure 6.88.
Pipe sticks should be supported along the pipe length at spans not exceeding 1m. See dimension B in Figure 6.88.
Stacked coils may not exceed a height of 1.83m. See dimension A in Figure 6.89.
6.7.1.2 Storage – Fittings
• Fittings are to be stored in cool, dry conditions under cover.
• Fittings should be stored inside their individual plastic bags and boxes.
• Keep the protective packaging intact until fittings are ready for use.
Figure 6.88 Storage of pipe sticks
6.7.1.3 Materials Handling – Pipe
• Pipes should be transported by a suitable vehicle, having a flat and level load bed with no sharp objects or projections, and able to support the complete plan area and weight of the pipe being transported.
• During transport, pipe sticks should be supported along the pipe length at spans not exceeding 1m.
• Coils may be transported on edge, provided:
• The coils are secured against a support suitably protected so as to prevent chaffing of the pipe surface.
• The coils remain in this position for only a limited period of time during transport.
• During transport, all loads should be securely anchored with suitable ratchet webbing loadstraps so as to prevent movement and chaffing of the pipe.
• The loading and unloading of pipe should be under trained and experienced supervision.
• Wide band slings of a non-metallic material should be used when lifting pipe bundles by crane. Do not use hooks, chains or hawsers.
• Pipe lengths of 6m and 8m, and coils may be loaded or off-
loaded using a forklift, provided the fork edges are suitably covered so as to prevent any damage to the pipe.
• Fork edges may be protected using lengths of HDPE pipe which have been slit open along the length, enabling a single pipe section to be pushed over the entire fork length. The slit along the pipe should be positioned so as to face down.
• Lifting points along pipe lengths or pipe bundles are to be evenly spaced.
• The dragging of pipe along the ground should be avoided.
• Scratches or striations deeper than 10% of the pipe wall thickness would void the pressure rating of the pipe and the use of such damaged pipe is not permitted.
• The use of a pipe section that has been kinked is not permitted except where an electrofused reinforcing coupler has been used to repair the kink.
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Materials Handling - The Unwinding of Pipe
Coils
In order to avoid accidental injury when unwinding pipes from
drums or coils, it is essential to ensure that the pipe end does not
spring outwards when loosening the fastening, as considerable
forces are released, particularly from larger diameter pipes.
Pipes with a diameter (nominal bore) up to 90mm can be unwound
from the coil, where the coil is held in an upright position whilst
securing the outside pipe end on the ground and releasing coil restraints one at a time. Petroplas pipe coils have multiple fasteners
that should only be loosened as pipe is unwound from the coil. See
Figure 6.90.
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The flexibility of HDPE pipe is subject to the ambient temperature.
For cold conditions up to -40˚C, a Salamander indirect oil fired
heater may be connected to a specially fabricated box or trailer
able to contain the pipe. See Figure 6.92. The pipe may be heated
until more flexible, taking care not to exceed the maximum temperature of 60˚C. Under no circumstances may exhaust gas emissions be used to heat the pipe.
Temperature changes cause alterations in pipe length and this
must be taken into account when cutting and installing pipelines.
Figure 6.92 Plan view of coil heating box
For larger diameter pipe, the use of an unwinding mechanism is
recommended. The coil can be laid flat on a rotating wooden or
steel cross and be unwound from the outside end. Coil fasteners
should only be loosened as the pipe is unwound from the coil.
See Figure 6.91.
Pipes must be unwound in such a way so as to avoid any buckling.
Spiral unwinding must be avoided as this will cause the pipe to
buckle.
Figure 6.90 Unwinding of pipe coils
This aspect is addressed in Section 6.7.2 Installation.
6.7.1.5 Materials Handling – Fittings
Figure 6.91 Unwinding mechanism
• Fittings should not be thrown.
• Under no circumstances should the electrofusion surface be touched.
• Fittings are to remain in their original packaging until ready for use.
• Electrofusion fittings should have a barcode on them.
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6.7.2 Installation
The Petroplas System must be installed in accordance with the latest version of these instructions as published by Marley Pipe Systems, the NFPA 30A standard, prevailing government regulations
or codes and customer specifications. The manufacturer should be
consulted where any standard, specification or regulatory code is
in conflict with the Petroplas installation instructions.
All pipelines are either single lengths of pipe or formed from short
lengths of pipe electrofused together to form a single homogenous
pipeline. The following subsections will describe in detail trench requirements, the laying of pipe, the joining process and backfill.
•
•
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Pipelines must be laid with a continuous fall back to the nearest drainage point, with a minimum gradient not less than 1 in 200 but preferably 1 in 100. Changes in gradient are permitted but pipeline sagging is not acceptable.
Changes in geological structure resulting in differential load bearing capacities of the trench base must be compensated for by suitable measures and referring to the design
engineer in order to prevent super imposed stresses along the pipeline.
Figure 6.93 Trench dimensions and pipe separation
6.7.2.1 Pipe trenches
Pipe trenches must enable installation of pipelines at a depth sufficient to prevent damage imposed by earth and/or traffic loads.
• The minimum cover depth for normal road traffic loads is 300mm above the crest of the largest diameter pipe. See dimension A in Figure 6.93.
• Excavation of all trenches must be at least 150mm. deeper than the required depth. The trench is then brought back to the correct depth by placing a number 10 to 5 sieve size (ASTM E-11), stone-free aggregate of either river sand or pea shingle. See dimension B in Figure 6.93.
• The trench bottom should be evenly finished so as to provide consistent support throughout the entire pipeline.
• Where two or more pipelines are laid along the same trench, the distance separating the pipelines (dimension C in Figure 6.93) must be equal to the largest pipe diameter (dimension D in Figure 6.93) being used in the trench. Short pieces of pipe from the larger diameter pipe may be cut for use as temporary spacers between adjacent pipe sections.
• Referring to Figure 6.93, minimum trench widths may be calculated as follows:
• TW = AP+2(CL) where:
•TW = Minimum trench width (dimension E).
•AP = Aggregate dimension of all the pipes laid in the
trench, including the minimum pipe separation dimensions (dimension F).
•CL = The clearance required on each side of the pipeline
(dimension G), determined by applying a factor of 2 to the largest pipe diameter being used in the trench (dimension D).
• Petroplas pipe runs should be laid in a pattern incorporating directional changes in order to compensate for pipeline movement within the prescribed granular bed.
• Referring to Figure 6.93, trenches should be widened in areas having to accommodate directional changes on the outside of the radius or bend in order to meet this requirement (dimension G). A factor of 4 (instead of 2) may be applied to the largest diameter pipe being used in the trench (dimension D) to meet this additional requirement. Pipelines should be laid accordingly.
6.7.2.2 Pipe laying
•
•
•
•
234
The laying of pipe from a coil is best done during the warmest part of the day as this will facilitate the unwinding process. Care should, however be taken when cutting pipe, as shrinkage could take place when the pipe cools down.
Designers and contractors should be aware of the differential rates of expansion and contraction between primary carrier and secondary containment sleeves where Petroplas Co-axial Pipe is being placed.
The primary carrier line should be free to move within the secondary containment sleeve and be terminated with flexible
hosing on either end.
Pipe bends should be at a radius equal to or greater than 25 times the pipe diameter.
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6.7.2.3 Backfill and bedding
All pipelines must be installed with adequate protection against
mechanical damage, where the protection is to remain effective
throughout the operational lifetime of the installation. The
prescribed bedding and backfill will ensure that pipelines remain
adequately protected.
• High water tables may require the placement of a geotextile membrane to prevent migration of the granular material in
trenches.
• When pipes are to be installed in steep areas, appropriate precautionary measures should be taken so as to avoid the pipe’s embedding being washed away.
• All temporary levelling supports and spacers must be
removed prior to the commencement of backfilling.
• Petroplas pipe is laid on a 150mm bed of a number 10 to 5
sieve size (ASTME-11), stone-free aggregate of either river sand or pea shingle.
• Thereafter, the pipe is finally covered with another 150mm of the same granular material. See dimension H in Figure 6.93.
• Where the temperature of the pipeline is expected to exceed that of the trench due to direct sunlight, the pipeline should be left to stand covered by the river sand or pea shingle prior to final filling and consolidation, for a time sufficient to allow the pipe to cool down.
• Final filling must be carried out according to PEI RP100 (Installation of Underground Liquid Storage Systems). Mechanical devices may be used, provided that the
permissible filling height is observed. Final compaction on top of the trench should be equivalent to ASTM D-1557 95%
6.7.2.4 Jointing method
Petroplas pipe sections and HDPE spigot ends are joined using
the FRIATEC® electrofusion weld process, ensuring safe efficient
processing and maximum joint integrity with error reporting. The
FRIATEC® system offers a complete range of FRIALEN® safety fittings with transition to metal systems, dedicated FRIAMAT® ancillary fusion-weld equipment and FRIATOOL® technical equipment
for the efficient preparation of all joints to be electrofused.
For the purpose of this instruction, the correct assembly of couplers, elbows, reducers, tees and transition fittings from the FRIALEN® safety fittings range has been detailed. Electrofusion for
large bore applications and other specialist fittings available from
the FRIALEN® safety fittings range is beyond the scope of this instruction manual. For such applications, the manufacturer should
be consulted as to the suitability of the specific fitting and for the
appropriate training.
6.7.2.5 General requirement
The integrity of any single joint affects the integrity of the entire
system. It is essential that all of the required joint preparations and
instructions are followed meticulously.
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• Use of the dedicated FWA315, FRIAMAT® Prime or FRIAMAT® Memo fusion units is compulsory.
• Installation personnel are required to be competent with the use of the fusion unit selected for use.
• The particular fusion unit’s operating instructions are to be observed at all times.
• When using the FRIAMAT® fusion units with traceability function, EF fittings can be traced back to source via a special barcode. This tracing data may be electronically archived together with the fusion processing data.
• Fusion units are to be kept in good working condition and serviced. Fusion whilst the medium is leaking out is not permitted. Under such conditions, fusion may only be performed provided;
• The line has been inerted with nitrogen,
• A FRIALEN® repair sleeve has been installed and the joint is not leaking. Prior to fusion, pipes and fittings should
have settled to a balanced temperature level between -20˚C and 50˚C.
6.7.2.6 Fusion procedure summary
An in-depth description of the steps below has been given in the
following section.
1. Clean pipe/spigot ends, cut pipe ends square and deburr.
2. Mark insertion depth and fluorination removal check lines on pipe/spigot ends.
3. Completely remove the fluorination layer, remove swarf and chamfer the pipe/spigot ends.
4. Clean pipe/spigot ends with recommended cleaner and re-mark insertion depth mark.
5. Apply rounding clamps on pipe/spigot ends.
6. Insert pipe/spigot ends into fitting and remove rounding clamps thereafter.
7. Stabilise the joint using a holding clamp.
8. Connect fusion unit, weld and disconnect.
9. Using the recommended marker, note all of the required
information on the fitting or pipe.
10. Allow the joint to cool for the recommended cooling time.
11. Remove the holding clamp.
6.7.2.7 Detailed fusion procedure
WARNING; the sequence of working operations described below
must always be adhered to.
• Select the correct FRIALEN® safety fitting for the application
• Carefully clean the pipe or HDPE spigot ends.
• Cut the pipe end(s) to length. Cuts are to be executed perpendicular to the pipe axis with the aid of a suitable pipe cutter (Figure 6.94). Deburr the outer and inner cut edges on the pipe or spigot ends using a hand scraper tool.
• A pipe which has not been cut off square may lead to the heating coil not being fully covered by the pipe or spigot end and this can cause overheating, uncontrolled melting or spontaneous ignition.
• Distinctive conical oblique pipe ends or any other pipe damage must be cut off.
• There may not be any surface damage such as grooves or
scratches within the fusion zone.
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• Carefully remove the FRIALEN® safety fitting to be used Figure 6.95 Remove fitting from packaging
from the original packaging (Figure 6.95). Inspect the fitting for any visible damage and ensure that the barcode label is attached. The fitting should be kept clean, avoiding accidental contact with the fusion-weld surface.
• Measure off the fusion zone on the pipe and/or HDPE spigot ends, marking it with a FRIALEN® marker or any other permanent metallic silver marker for the removal of the
fluorination layer (Figure 6.95 and 6.97).
• The fusion zone may be determined by measuring from the insertion depth tab to the fitting’s edge. An allowance of 5mm in addition to the insertion depth will ensure that the fluorination layer was correctly removed.
• As a check that the removal of material from the pipe/ spigot surface is unbroken and covers the full area, we recommend the marking of checking lines (Figure 6.97).
• Before joint assembly, the Teflon® like layer, which has formed on the surface of pipes and HDPE spigot ends due to oxidation and fluorination, must be completely removed
using either a hand scraper tool or the appropriate FRIALEN® Figure 6.96 Measuring the fusion zone
scraper tool. Only material in the fusion zone needs to be
removed.
• All fusion area markings, including the fusion depth mark, need to be completely removed (Figure 6.98 and 6.99).
• A one-off complete scraping process of the surface is
sufficient, removing a minimum of 0.15mm material.
Figure 6.94 Cut pipe ends square
Figure 6.97 Checking lines
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• Failing to completely remove the Teflon® like layer may lead to a fused joint which is not homogeneous and which may leak.
• The condition of the manual scraper blade and the scraper tool blade should be checked regularly and replaced if found to be worn.
• If during the scraping process, localised areas of the surface are not scraped, these must be redone.
• When using the hand scraper tool, always commence scraping from behind the fusion depth mark, ensuring that the stroke extends over the pipe or spigot end. See Figure 6.100. Even when localised areas of the surface are not scraped, the correcting strokes are to be from behind the fusion depth mark, scraping towards the pipe or spigot end.
• The use of filling or emery cloth in order to remove the oxide layer is not acceptable, as this can lead to impurities being embedded in the surface.
• Warning: the removal of an excessively large amount of shaving can leave a large annular gap which cannot be closed, or completely closed, during fusion.
• After scraping, do not touch the fusion zones again.
• Using a hand scraper tool, chamfer the outside surface of the cut pipe or spigot end, making it easier to fit the coupler (Figure 6.101).
• Remove all resulting swarf from all surfaces, including the inside surface.
• There may not be any pipe or spigot end surface damage such as grooves or scratches within the fusion zone.
• The operating instructions for the FRIATOOL® scraper tools FWSG 63 and FWSG 225 have been included in following Section 6.7.3 Using the FRIATOOL® scraper tools.
• Protect the worked zone from dirt, soap, grease, water running back and environmental elements (e.g. from effects
of moisture or the formation of frost). This may be done by placing clean plastic bags, fastened with tape or zip ties over pipe or spigot ends (Figure 6.102).
• Worked pipe or spigot ends need to be fused within 4 hours of the scraping process.
• FRIALEN® Safety Fittings with integral heating coils ensure optimal heat transfer due to their exposed coils and because
of this, the inside of the fitting must not be scraped.
• The surfaces of the pipe or spigot ends being fused and the internal fusion surfaces of the FRIALEN® safety fitting(s) (Figure 6.103) must be absolutely clean, dry and free from grease.
• Immediately before assembly and after scraping, clean these surfaces using IPA (isopropyl alcohol), acetone, MEK, ether,
white spirits or non-coloured denatured alcohol with an absorbent, lint-free, non-coloured paper towel (Figure 6.104).
Dispose of the paper towel after cleaning and use a new towel for each joint.
• When cleaning, take special care to avoid dirt from the unscraped pipe surface being introduced into the fusion zone (Figure 6.105).
• After cleaning with the solvent, do not touch the fusion zones again.
• The cleaner must have evaporated completely before fusing.
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Figure 6.98 Removal of oxide layer
Figure 6.99 Complete removal of oxide layer from fusion zone
Figure 6.100 Using the hand scraper
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• Using the FRIALEN® marker (or other permanent metallic silver marker), re-mark the line (using approximately a 120°
distribution around the circumference) to show the width of the fusion zone on the pipe or spigot end, since this mark will have been removed by scraping (Figure 6.106).
• Ensure that the fusion zones remain clean and untouched. If necessary, repeat cleaning with the solvent.
• Insert the pipe or spigot ends into the fitting, taking care that the contact sockets remain accessible for connection of the fusion plug.
• For out of round pipe, apply the rounding clamps over the pipe or spigot ends, about 13mm deeper than the fusion depth mark.
• The worked pipe or spigot end must be pushed into the fitting up to the fusion zone mark. Rounding clamps
may now be removed.
• All joints assembled for fusion must be free of stress.
• Pipe or spigot ends may not be inserted into any
FRIALEN® safety fitting under a bending stress or
under a load from their own weight.
• Pipe or spigot ends must be supported by a suitable
holding device.
• After completion of the fusion process, the stress-free support of the joint must be maintained until the cooling time given on the barcode of the fitting has elapsed.
• A joint which is not free of stress or which is displaced can lead to an unacceptable flow of molten material during the fusion process and this can lead to a defective joint.
• Before fusing, check once again by means of the fusion line marks that the pipe or spigot ends in the FRIALEN® safety fitting have not moved. If necessary, correct this.
• Connect the fusion plugs to the contact sockets and power on the fusion unit (Figure 6.107).
• Fusion parameters are contained in the fitting information barcode on the FRIALEN® safety fitting with the FRIAMAT® Memo or Prime fusion units, the parameters are entered into the fusion unit using the barcode wand. Hold the wand at an angle and scan the barcode using an even stroke. The barcode may be scanned from any direction (Figure 6.107).
• After entering the barcode, the fitting and pipe to be fused should be compared to the data being displayed on the fusion unit. If all of the information (fitting and pipe SDR stage) is correct, confirm the fusion unit’s prompt and proceed.
• The secondary barcode contains the data for component traceability. This barcode must be entered only if component traceability is to be used.
• Always replace the barcode wand in the pouch when scanning is complete.
• Fusion parameters and traceability data is coded on the barcode sticker of all FRIALEN® safety fittings using a 24 and 26 digit code respectively. Both codes may be entered manually into the FRIAMAT® fusion unit via the emergency programming mode in the case of a barcode failure.
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Figure 6.101 Chamfer pipe / spigot ends
Figure 6.102 Protected pipe / spigot ends after working
Figure 6.103 Cleaning the fitting fusion zone
Figure 6.104 Clean worked pipe / spigot ends with suitable
cleaner
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• After scanning the fusion parameters and traceability code, the unit prompts users to confirm that the joint has been suitably prepared and stabilised. Confirming this prompt will start the fusion process.
• For the sake of general safety, always maintain a distance of 1m from the fusion point during the fusion process.
• Should there be an interruption, for example a power failure, fusion may be repeated after the particular fitting’s cooling time (CT) has elapsed.
• For fittings with separate windings, each end of the fitting has to be fused separately. For fittings with a continuous winding, the two ends of the fitting are fused
simultaneously.
• The fusion unit automatically monitors the progress of the fusion process and regulates the electrical energy
supplied to specified limits. The unit will beep when fusion is complete.
• The fusion plugs may be removed.
• FRIALEN® safety Fittings are equipped with fusion indicators that increase in volume, giving indication that fusion has taken place. However, the proper progress of the fusion process may only be confirmed by the fusion unit on
completion.
Figure 6.107 Connect and scan
Figure 6.105 Do not introduce dirt from the unscraped pipe end
Figure 6.108 Weld markings
Figure 6.106 Re-check insertion depth
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6.7.3 Using the FRIATOOL® Scraper Tools
Figure 6.109 FWSGE 4 Scraper Tool
6.7.3.1 FWSGE 63 for 20mm to 63mm
applications
• Referring to Figure 6.109;
• Release the roller handle (1).
• Set the guide rollers (2) according to the pipe size being scraped by releasing the guide clamp (3) in a
counter-clockwise direction. There are two positions indicated
on the unit. Tighten after setting.
• For pipes of diameter 20mm to 40mm
• For pipes of diameter 50mm to 63mm
• Remove the protective cap from the scraper blade.
• Turn the twist grip knob counter-clockwise until the scraper tool is able to fit over the pipe end. The pipe should be nested
between the smooth and knurled rollers. For pipes of diameter 20mm to 40mm, place the scraper blade on the fusion depth mark as indicated on the pipe section.
• Scraping will be from the fusion depth mark toward the pipe end.
• For pipes of diameter 50mm to 63mm, place the scraper blade on the pipe end. Scraping will be from the pipe end towards the fusion depth mark.
• Tighten the twist grip knob firmly.
• Using the roller handle, continuously rotate the scraper tool around the pipe axis in a clockwise direction until the oxide layer is completely removed to the indicated fusion depth mark or to the pipe end.
• Loosen the twist grip knob (4) and remove the scraper tool from the pipe end.
• Remove the swarf and inspect the scraping result. If the marking lines are not completely removed, the scraping process should be repeated.
• Tighten the twist grip knob (4) until fully seated and collapse the handle (1) to the storage position by gently pulling whilst
simultaneously folding.
• The scraper tool must be kept clean and dry and always stored in its transport case.
• Keep the blade covered (5) in order to prevent accidental injury.
• The condition of the tool blade should be checked regularly and replaced if found to be worn.
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6.7.3.2 FWSGE 225 for 75mm to 225mm
applications
Figure 6.110 FWSGE 3 Scraper Tool
• Referring to Figure 6.110;
• Fully open the clamping carriage by turning the twist grip knob (1) anti-clockwise. Hold the scraper tool by the roller handle (2) and point it towards the floor. Turn the tool anti-clockwise with twisting movements until it reaches the mark for the required scraping dimension.
• Check every 5 to 10 turns to see if the mark has been reached.
• The line to the right of the nominal pipe diameter must be flush with the housing.
• Remove the protective cap (3) from the scraper blade.
• Guide the tool over the pipe end so that the clamping carriage (4) is inside the pipe and the scraper blade is on the outside
surface of the pipe. Turn the twist grip knob (1) clockwise until all four guide rollers are pressed firmly against the pipe.
• Continuously rotate the tool clockwise around the pipe axis, scraping up to the pipe end. Note that the tool should be pressed against the pipe end while scraping in order to avoid tilting of the tool in an axial direction.
• Release the twist grip knob (1) by turning it anti-clockwise. The scraper tool may now be withdrawn from the pipe.
• Remove the swarf and inspect the scraping result. If the marking lines are not completely removed, the scraping process should be repeated.
• Replace the blade cover (3).
• Hold the scraper tool by the roller handle (2) and point it towards the floor. Turn the tool clockwise with twisting movements until it reaches the initial position for storage.
• The scraper tool must be kept clean and dry and always stored in its transport case.
• The condition of the tool blade should be checked regularly and replaced if found to be worn.
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6.7.4 Pressure Testing
Petroplas installations are to be tested in one of two ways before
the trenches are closed. The consulting engineer or project
manager may specify that the tests be used independently or
in conjunction with each other.
• For primary carrier pipes, the test pressure must correspond to the pipe’s rated pressure.
• For secondary containment testing, the test pressure must correspond to the lesser of the pipe’s or test boot’s rated pressure.
6.7.4.1 Hydrostatic method
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• The most ideal situation would be to leave the pipeline under pressure for 24 hours where the pressure is preferably checked at the same time of day.
• As gas is very susceptible to temperature change, and expands and contracts proportionally, it is important to note that there will be a pressure variance (positive or negative) on the gauge.
• Small leaks are more difficult to detect using the pneumatic method.
• The secondary containment system should be tested using the same procedure with all interstitial spaces connected as described in the Hydrostatic test method.
6.7.4.3 Record keeping
• The pipeline is filled with water from the highest point of the installation.
• All air is removed from the system, by opening all valves until the water level reaches the top of the valve at which point
the valve is shut.
• Once all the air has been removed from the system and the pipe is completely filled to the highest point, the pipe is connected watertight to a pressure pump using the required metal fittings.
• The water in the pipe is pressurised to test pressure.
• As water is not compressible, leaks will show up immediately if the pressure gauge does not maintain its static pressure reading. Note that due to pipe elasticity, some time must be allowed for the pressure to stabilise.
• The test is successful once full pressure has been attained and maintained for a period of 1 hour.
• The secondary containment system should be tested using the same procedure following the setup detailed below:
• All test boots along the pipeline are fitted and secured over the terminated secondary containment pipe ends. The primary pipe clamps on the test boots are also secured.
• All terminated secondary containment sections are connected with jumper pipes having a higher pressure rating than the test pressure.
• All interstitial spaces are now interconnected for test purposes.
6.7.4.2 Pneumatic method
• Either air or nitrogen is pressurised in the line to the rated pipe pressures.
• Air may only be used in new installations.
• Nitrogen should be used as the pressurising gas where hydrocarbons have been introduced in the pipe system, including new lines connected to existing installations.
• The gas in the pipe is pressurised to test pressure.
• Once the lines have been pressurised, a soap and water test should be performed on each fitting of the pressurised line.
• A soap and water solution is mixed and applied at the pipe to fitting interface.
• Observe for the formation of any bubbles, in which case a leak is present.
• The test is successful once full pressure has been attained and maintained for a period of at least 4 hours but preferably 24 hours.
Contractors are required to submit via email an electronic warranty
card containing the details of completed or repaired installations.
The cards, in PDF format, are available from either Marley Pipe
Systems or the Nominated Petroplas Agent and should be returned
to the designated email recipient no later than 30 days after an
installation or repair has been completed in order to validate the
warranty.
The following information will be required on the warranty cards:
• Responsible contractor
• Site name, site number and location
• Date sitework commenced
• Date when installation was completed
• Accredited Petroplas Installation Personnel used and the designated initials as marked on all electrofusion welds.
• Petroplas pipe used in the installation with batch numbers
• Number of electrofusion welds completed on the site
• Site inspector
• Appointed engineer
Contractors may also be required upon request, to furnish for any
installation or repair:
• The original FRIAMAT® Memo slips or records where possible.
• The approved site plans and working drawings.
• The dated and signed Quality Control Inspection Sheet.
It is important to emphasise that the information noted on joints
where electrofusion has been completed form an integral part of
the record-keeping requirements.
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6.7.5 Guidelines for Holding Device
5
2
2
4
2
2
3
A
1
Figure 6.111 Holding device
1. U-channel of steel or aluminum with dimensions enabling the pipe to be nested on top, supported by the two channel flanges,
2. Ratchet webbing loadstraps, placed as close to the fitting and channel ends as possible
3. Petroplas Pipe
4.FRIALEN® Safety Fitting
5. Part of U-channel milled away so as to prevent channel from interfering with the fitting. Dimension A should be at least the fitting length plus the pipe diameter multiplied by a factor of 6. Alternatively, a more elaborate mechanism may be constructed where multiple rounding clamps are aligned on a rail or series of parallel rails able to support the joint. Dimension A would still, however be applicable to the design, as would the positioning of the rounding clamps replacing the ratchet webbing loadstraps.
Table 6.15 Guidelines for holding device
FRIALEN® Fitting
diameter in mm
CT
Test Pressure
Max. Pressure
Cooling time before joint can be moved, also indicated on
FRIALEN® fitting barcode
Cooling time required in minutes before the joint may be
tested at 6 Bar (87 psi)
Cooling time required in minutes before the joint may be
pressurised to the maximum rated pressure
20 – 32
5
8
10
40 – 63
7
15
25
75 – 110
10
30
40
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7. DETAILED DESIGN................................. 244 - 282
7.1 Length Changes Due to Temperature and 245
Pressure
7.2 Calculating Forces......................................246 - 253
7.3 Elasticity Test..............................................253
7.4 Calculating the Stresses.............................253 - 255
7.5 Expansions................................................. 256
7.6 Estimating Service Life............................... 256
7.7 Sample Calculation.....................................256 - 259
7.8 Miners Rule................................................ 260 - 261
7.9 Graphs....................................................... 262 - 280
7.10 Applied Formulas and Abbreviations......... 281 - 282
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7.1 LENGTH CHANGES DUE TO TEMPERATURE AND PRESSURE
7.1.1 Temperature Length Change
Exposing a pipe system to varying temperatures (e.g. ambient and
operating temperatures) changes its status with regard to the expansion capacities of individual pipe sections. Pipe sections designate the distances between the system point in question to the
relevant fixed point. The thermally conditioned length change
( ) of individual pipe sections is calculated as follows:
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In calculating temperature difference ( ), care should be taken
that the lowest and highest temperatures (installation, operating
and stationary) are used in the calculation. Approximations usually
take just flow medium and ambient temperatures into account. The
simplest type of compensation for length changes in thermoplastic pipe installations involves using L-form expansion bends (90°
changes of direction). L-bends are also referred to as elbows. The
minimum dimensions of an elbow, as illustrated in Figure 7.1, is
indicated by the following equation:
Equation 7.4
Equation 7.1
LPipe
max
= thermal length change (mm)
= pipe length (m)
= thermal expansion coefficient (K-1)
= max. temperature difference (K)
7.1.2 Length Change Due to Internal Pressure
Loads
LB
L1,2
de
EcR
t sf acc
= length of the expansion bend (mm)
= system lengths of expansion bends (mm)
= outside diameter of the pipe (mm)
= expansion (-)
= (average) bending creep modulus of the pipe material for = 25a (N/mm²)
= acceptable flexural stress share for t = 25a (N/mm²)
In any closed pipe string, a longitudinal expansion is produced by
the occurrence of internal pressure loads as follows:
Expansion bend lengths for L, Z and U bends are illustrated in
Graphs 7.1 to 7.4, and the corresponding values can be read from
these diagrams.
Equation 7.2
Figure 7.1 Elbow (L-bend)
=
pi =
EcR =
de =
di =
LPipe=
μ =
length change due to internal pressure (mm)
internal pressure (bar)
creep modulus of the pipe material (N/mm²)
outside diameter of the pipe (mm)
inside diameter of the pipe (mm)
pipe length (L1, L2,•••, Lx) (mm)
transverse contraction number (-)
7.1.3 Determining Expansion Bend Dimensions Length Change ( ):
Equation 7.3
LPipe= pipe length (m)
= temperature difference (K)
= thermal length change (mm)
7.1.4 Pipe Sections for Absorbing Length
Changes
As shown in Figure 7.2, length changes subject pipe sections to
bending. The dimensions of expansion bends (LB) are established
by the relationship:
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Figure 7.2 Pipe section for absorbing length changes
V a l u e
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Figure 7.3 Firmly fastened pipeline
7.2.1 Maximum force at fixed points without
compensation for length change
The largest fixed point load occurs at a firmly fastened pipeline,
and is calculated as follows:
Equation 7.6
Equation 7.7 to 7.9
Equation 7.5
LB
de
= length of the expansion bend (mm)
= expansion (-)
L1,2 = system lengths of expansion bends (mm)
EcR = (average) bending creep modulus of the pipe material for t = 25a (N/mm²)
= acceptable flexural stress (N/mm²)
f acc
7.1.5 Branch Connections
In pipe sections subject to axial movement, it is also important to
ensure that branching pipe strings are not exposed to high flexural
tensions. The minimum distance between a tee section and the
nearest guide bracket corresponds to the expansion bend length
(LB). With the aid of Graphs 7.1 to 7.4, the required expansion
bend lengths are visually illustrated.
7.2 CALCULATING FORCES
Fixed points in pipe installations are brackets that fix the pipe in x, y
and z directions. The forces at these points depend on the nature of
the individual pipe system. The "slacker" the pipe running between
two fixed points is, the smaller the reaction forces generated by deformation effects. The exact calculation of the force components in
any given pipe system is laborious. The calculation is made easier
by the use of proprietary software for thermoplastic pipe systems.
Explanation of symbols in Equations 7.6 to 7.9
FFP = force at fixed points in a firmly fastened pipe string (N)
AP = area of pipe annular surface (mm2)
= constricted length expansion (-)
= maximum temperature difference between TL and TU (K)
pi = internal pressure (bar)
EcR = (average) creep modulus of the pipe material for t = 100 min (N/mm2)
de = outside diameter of the pipe (mm)
di = inside diameter of the pipe (mm)
μ = transverse contraction number (-)
Because the creep modulus is dependenton time, temperature and
stress, an average load period of 100 minutes is adopted for the
calculations. The corresponding values can be derived from Graph
7.5. The forces at fixed points can also be interpolated from Graph
7.5.
7.2.2 System-dependent Fixed-point Force
Thermoplastic pipes are usually installed so that the compensation
capacity of direction changes can be used to absorb length changes. Therefore, the resulting fixed point forces are system specific
and in most cases, they are smaller than the fixed-point load calculated in Section 7.5.
However, the procedure is simplified by adopting the largest possible load to design the fixed-point structure. If the load compensation measures indicate that the forces being prevented are large
enough, e.g. for pipe bridges, brickwork, containers and pump
supports, a system-specific calculation is an essential part of the
structural calculation. The calculation is made easier by the use of
proprietary software for thermoplastic pipe systems.
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Graph 7.1 L-expansion bends
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Graph 7.3 U-expansion bends
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Graph 7.4 Z-extension bends
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Graph 7.5 Creep modulus for PE100
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7.2.3 Forms of Compensation in Level Pipe
Systems
7.2.4 Rough Calculation of Fixed-point Forces
in L-bends:
Figure 7.4 Forms of compensation in level pipe systems
Equation 7.11
FLB =
l =
EcR =
JP =
LB =
fixed-point load at (L, Z, U) bends -> Fy or Fx (N)
length change (mm)
(average) creep modulus of the pipe material for t = 100 min (N/mm2)
pipe moment of inertia (mm4)
length of the expansion bend (mm)
Equation 7.12
JP = pipe moment of inertia (mm4)
7.2.5 Fixed-point Force in Cases of Constricted Length Change Due to Internal Pressure
Load
Equation 7.13
Explanation of Figure 7.4:
Fx , Fy , Fz = force components
Fy, Fx = FT at fixed points "A" and "B"
= transverse force
FT = resulting total force
FR Z1 , Z2 , Z3 = distances of the system points from the line of action
S
= system centre of mass
The distance (Z) (lever) and the resulting total force (FR) produces the moment (M)
=
a
AP =
FFP =
d e =
di =
axial stress (N/mm2)
area of pipe annular surface (mm2)
force at fixed point (N)
outside diameter of the pipe (mm)
7.2.6 Fixed-point Force in Cases Involving
Compensators or Expansion Couplers
Equation 7.14
Equation 7.10
at a given position of the individual pipe system
AK =
pi =
d i =
FFP =
M = moment of torque (Nm)
FR = resulting force (N)
Z = lever (m)
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surface subject to pressure (mm2)
internal pressure (bar)
force at fixed point (N)
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7.2.7 Resulting Force at Fixed Point
Brackets are subject to both horizontal and vertical loads and
simultaneous loads in both directions produce a resulting total
force (FR).
Equation 7.15
V a l u e
P a r t n e r
To establish the multi-axial state of stress requires calculation of
the resulting stress ( res) and comparison with the value for ( acc).
In particular, failure to account for flexural stresses around expansion bends and the tensile stresses resulting from impeded thermal
expansion can result in failure of a pipe that is, otherwise subject to
a small internal pressure load.
7.4.1 Axial Stress (X Axis) Due to Internal
Pressure
FB =axial fixed-point force (FFP) or friction force (Fμ) as a result of a length change in the pipe string
FV =transverse force (FTV) for fixed-point load and/or pipe weight (FW) between two brackets with or without additional load.
7.3 ELASTICITY TEST
Elasticity tests on pipe systems serve predominantly to calculate
force actions and stresses.
Stresses are created by:
- internal pressure loads
- constricted longitudinal movement under temperature change
- bending of bend sections when absorbing length changes
Equation 7.16
7.4.2 Tangential Stress (Y Axis) Due to Internal
Overpressure
Equation 7.17
The forces affecting fixed points not only cause bending moments
in the bend sections but also in the firmly fastened sections. In
3-D systems, the pipeline is also subjected to torsion. For facilities
corresponding to load classes II and III or requiring testing or monitoring in general, the elasticity calculation is not only a criterion for
careful design but also partly prescribed.
7.4 CALCULATING THE STRESSES
ARISING IN A PIPE SYSTEM
7.4.3 Radial Stress (Z Axis) Due to Inner Overpressure
Pipe systems are usually exposed to a multi-axial stress state. The
stress measured in the pressure creep test (Graph 7.6) provides
the basis for designing thermoplastic pipe systems. The layout of
pipes is generally based on the internal pressure load, which corresponds to the load in the internal pressure creep test.
Equation 7.18
Figure 7.5 Radial (
r
), Axial (
a
) or Tangential ( t) stress
7.4.4 Flexural Axial Stress (X Axis) in a
Straight Pipe between Brackets
Equation 7.19
However, in addition to the stresses in the axial, radial and tangential directions to the pipe axis, which are usually caused by heat
or internal pressure loads, there are other stresses, e.g. flexural
stresses, created in a pipe system, making it necessary to investigate all the stress components as part of a structural analysis.
7.4.5 Flexural Stress in Bends
Equation 7.20
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Graph 7.6 Reference stress for PE100
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Mb from the elasticy test
V a l u e
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Equation 7.28
Equation 7.21
7.4.8 Calculating the Resulting Stress
Equation 7.29
Equation 7.22
Equation 7.30
Equation 7.23
Equation 7.31
7.4.6 Stresses Due to Constricted Thermal
Expansion
Equation 7.32
Maximum stress value in a short-term perspective:
Equation 7.24
Equation 7.33
In a long-term perspective:
Stress for temperature = constant
Explanation of symbols in Equations 7.16 - 7.33
Rp = moment of resistance of the pipe (cm3)
Mb = bending moment due to the tensile or compressive forces affecting branch sections
LB = bracket distance (m)
JP = pipe moment of inertia (cm4)
R = bending radius of bends (mm)
ra = average pipe radius (mm)
q = weight of the full pipes (N/m)
e = pipe wall thickness (mm)
di = inside diameter of the pipe
EcR = average creep modulus of the pipe material (N/mm2)
i = internal pressure (bar)
= stress in straight pipe (N/mm2)
0
= axial stress (N/mm2)
a
= tangential stress (N/mm2)
t
= radial stress (N/mm2)
r
= flexural stress (N/mm2)
f
= axial stress due to constricted thermal expansion (N/mm2)
= maximum axial stress due to constricted thermal max
expansion (N/mm2)
=
resulting stress (N/mm2)
res
=
direction-dependent stress (N/mm2)
x, y, z
= acceptable stress (N/mm2)
acc
TsP = inner pipe wall temperature (°C)
TeP = outer pipe wall temperature (°C)
B = bend factor (-)
a = thermal expansion coefficient (K-1)
Equation 7.25
Stress for temperature = variable
Equation 7.26
Tensile stress arises when the period of low operating temperature (tcold) is shorter than the period of high operating temperature
(twarm) , i.e. tcold < twarm
Equation 7.27
7.4.7 Residual Stress Due to Temperature Differences between Inner Pipe Wall and Outer
Pipe Wall
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7.5 EXPANSIONS
7.6 ESTIMATING SERVICE LIFE
If pipe deformation exceeds certain creep limits, flow zones and
microscopic cracks are created across the direction of expansion.
For usual applications, pipe deformation is calculated in the following manner.
If the calculation variables, temperatures and their reaction time
in relation to the assumed total load period are all available, the
expected service life can then be determined. The calculation of
the service life, however involves a high degree of mathematical
complexity. For this reason, a closer examination of the mathematical determination of a pipe system's service life will be set aside.
Equation 7.34
When calculating the service life, it must be noted that it is also
affected by chemical and physical conditions. A detailed treatment
of the topic of service life, complete with examples, is contained in
the German DVS 2205-1 guideline.
Equation 7.35
The calculation of service lives involving varying loads requires extensive knowledge of the handling of plastics. The calculation is
made easier by the use of proprietary software for thermoplastic
pipe systems.
, y =
x
, y, =
x
EcR =
μ =
expansion along the x and y axes of stress in a multi-axial load (-)
stress along the x, y and z axes (N/mm2)
average creep modulus of the pipe material (N/mm2)
transverse contraction number = 0.38 (-)
7.7 SAMPLE CALCULATION
A number of values will be calculated for the isometric pipe system
illustrated below.
Figure 7.6 Pipe isometrics
The largest expansion is calculated on each occasion and compared with the threshold value ( F) The requirement reads:
Equation 7.36
= expansion threshold value
= x or y (-)
max
F
Table 7.1 Expansion threshold value for PE
Material
expansion threshold value
PE
F
3%
Should the correlation between stress and expansion be expressed, it can also be included in the following relationship:
Equation 7.37
GB =guide bracket (guide saddle), which is a fixing with an axial pipe guide
FP = fixed point, which is a fixing without any possibility for movement
1 LM = support distance for the middle of a continuous pipe
2 LE = support distance for a separate or end piece, as well as the
self-supporting total pipe length of an L bend. If both bending lengths are, in total, longer than the acceptable support distance (LF), an additional SB is to be placed between the pipe bend and the GB
3 LV = guide bracket distance for an inclined pipe string. To absorb weight, a fixed point or bearing fixed point or support ring is to be provided for each string
4 LB = bending lengths for absorbing length changes and operating conditions
EcR = average creep modulus of the pipe material (N/mm )
= expansion (-)
= stress (N/mm2)
0
2
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Explanation of terms 1, 2, 3, 4 for Equations 7.38 to 7.45. The
numbering and short symbols provide information about the variables being calculated and where their location in the isometric diagram. The illustration is therefore a guide and helps the user to
obtain an overview of a pipe system and its calculations.
V a l u e
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Determination of the force components
Equation 7.39
7.7.1 Load on brackets
Brackets are subject to both horizontal and vertical loads. Simultaneous loads produce a resulting total force (FR), which can be
calculated using the following Equation 7.38. Figure 7.7 shows a
bracket with the effective forces and the calculated bracket distance (Bd).
Equation 7.38
FB = axial fixed-point force (FFP) or friction force (Fμ) as a result of a length change in the pipeline
FV = transverse force (FTV) for fixed-point load and pipe weight (FW) between two brackets with or without additional load
Figure 7.7 Pipe saddle load
μF = friction coefficient usually between 0.3 and 0.5
= force at fixed point (N)
FFP
FW
= weight (N)
FTV = transverse force (N)
Fw (Pipe)
= weight (pipe weight) (N)
FW (Fill med)
= weight (weight of fill medium) (N)
= weight (additional weight) (N)
FW (Add load)
7.7.2 Bracket distances (Bd)
The fixing distances of a plastic pipe shall be determined in such a
way that no excessive stresses arise both under operating conditions and during testing. Similarly, consideration is also to be given to the deflection limits of the pipe. The arrangement of various
brackets and their distances from each other can be seen in the
illustrated example (Figure 7.6) of pipe isometrics.
7.7.3 Calculating Acceptable Bracket Distances
Equation 7.40
LM = support distance for the middle of a continuous pipe (mm)
EcR = creep modulus of the pipe material for t = 25a (N/mm2)
facc = acceptable pipe deflection according to the recommendations in Table 7.2 (mm)
e = pipe wall thickness (mm)
= density of the pipe medium (g/cm3)
P
= density of the flow medium (g/cm3)
F
Equation 7.41
Equation 7.42
Values for Y:
257
< Ø de 110 mm
-> Y=1,1
Ø de125 - 200 mm -> Y=1,2
< Ø de 225 mm
-> Y=1,3
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Equation 7.43
Note to Equations 7.44 and 7.45:
LB = mathematical definition in Equation 7.28 respectively with
appendices B3 to B7
Axially constricted pipe systems operating at raised temperatures
or an expected reduction of the creep modulus (EcR) as a result of
chemical effects will both give rise to risks of buckling.
Explanation of symbols in Equations 7.41 to 7.43:
LM = support distance for the middle of a continuous pipe (mm)
LE = support distance for a separate and end piece, as well as the self-supporting total pipe length of an L bend.
LV = guide distance for an inclined pipe string (mm)
LB = length of the expansion bend (mm)
Y = factor (dependent on pipe dimensions) (-)
Raised operating temperatures are:
PE -> Tcrit > 45°C
PP -> Tcrit > 60°C
The buckling risk is strengthened due to bending along the pipe
axis or insufficient pipe storage practices. Bending can result from
too long support distances, improper storage of pipe and lasting
pipe impacts during welding.
To calculate the support distances, the following deflections are
recommended as acceptable values:
In such case, it is recommended that the buckling distances either
calculated or interpolated from appendix B10 are reduced by a factor of 0.8. Pipe systems with de < 50 mm should be equipped with
continuous support for economic reasons.
Table 7.2 Deflection facc for pipes
Ø de
20 - 110
125 - 200
225 - 355
400 - 600
facc
2 -3 mm
3 - 5 mm
5 - 7 mm
7 - 10 mm
If larger deflections are permitted, the pipe should not be axially
constricted.
7.7.5 Determining Pipe Deflection for Calculated Support Distances
7.7.4 Verifying the Acceptable Buckling
Length
Pipe deflection for the calculated support distance (LM) from
Equation 7.40 is determined by means of the following equation.
If pipes are installed so that axial expansion of all or individual lines
is no longer possible (axial constriction), the calculated fixing distance must be tested for its buckling resistance. To avoid the risk
of buckling due to restricted thermal expansion, the length of pipe
between two brackets must be no more than LK.
Pipe deflection for the calculated support distance (LE) from
Equation 7.41 is also determined by means of Equation 7.46.
Equation 7.46
Equation 7.44
See Graph 7.7.
LK acc
de
di = acceptable buckling length between two brackets (mm)
= inside diameter of the pipe (mm)
q = weight of the filled pipe along with any insulation (N/mm2)
EcR = creep modulus of the pipe material (N/mm2)
LM, LE = bracket distance (m)
LB = acceptable bracket distance (m)
JP = pipe moment of inertia (mm4)
fD = deflection (mm)
At position 3, the pipe is not subject to deflection but to buckling
The following applies to all pipe systems without linear compensation:
Equation 7.45
Values for LB are found in Graph 17:
LB acc = acceptable pipe length between two brackets (mm)
LS acc = available or calculated support distance according to equations 1, 2, 3 (Equations 7.40 to 7.42)
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Graph 7.7 Bracket distances in axial constricted PE100 pipe systems
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7.8 MINER'S RULE
The figure below shows the superposition of cumulative damage
at different temperatures.
7.8.1 Fatigue Damage Accumulation
Figure 7.8 Superposition of cumulative damage at different temperatures
In considering the design of pressure pipes so far, we have assumed a continually acting stress. However, if the stress is interrupted by periods in which the pipe is unstressed or if periods of
varying mechanical and/or thermal stress occur, we refer to this as
cyclic stress. In this case, it is important to ascertain how damage
accumulates during the individual stress periods and what the total
service life is likely to be.
To clarify these questions, HDPE pipe specimens with the dimensions 32 x 3mm produced from the unimodal Hostalen GM 5010
were placed under a stress of 3 N/mm² at a constant temperature
of 80°C for 6 hours and then relieved from the stress for 18 hours.
This cycle was repeated until the pipe specimens ruptured. The
time to rupture under stress average over 6 tests (integral stress
relief). It can be see then that, under the given test conditions, the
cyclic nature of the stress made practically no difference to the assessment of pipe creep strength value based on the test under
constant stress.
Hence, the theory of linear fatigue damage accumulation (Miner’s
Rule, superposition principle, ISO 13 760) applies. This postulates
a direct relationship between the point at which the cumulative
damage from the totality of stress cycles leads to failure and the
service life expectancy under constant stress. To convert lifecycle
values under constant stress to expected service life under cyclic
stress, the following approximation can be made: where t is the
time under the stress at temperature Δi, and ΔtR is the time to rupture, measured in hydrostatic strength test under the corresponding constant stress.
Equation 7.47
Example: Water is to be conveyed in a pressure line. The operating
pressure is a constant 6 bar. The temperature/time curve is specified as follows:
50°C during 3h per day
30°C during 21h per day
What SDR class according to DIN8074 must a
PE80 pipe have to ensure a 50-year service life
expectancy?
The overall service coefficient is assumed to be 1.6.
Over the total operating period of 50 years, the temperature-time
fractions add up as follows:
at 50°C: Δt1 = 6.25 years
at 30°C: Δt2 = 43.75 years
First, a pipe with a diameter/wall thickness ratio SDR = 11 is chosen.
The operating stress is:
Equation 7.48
Thus
Equation 7.49
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From the hydrostatic strength curves for PE80 pipes according to DIN8075, the following times to rupture are obtained at a constant
stress of 4.8 N/mm²:
at 50°C: t8 (ϑ1) = 13 years
at 30°C: t8 (ϑ2) >100 years (extrapolated)
The damage contributions are thus:
Δt1/tR (ϑ1) = 6.25/13 = 0.48 = 48%
Δt2/tR (ϑ2) = 43.75/100 = 0.44 = 44%
Equation 7.50
The value calculated according to Equation 7.50 must be < 1 or < 100%.
The chosen diameter/wall thickness ratio (SDR 11) is correct for this application.
For partially crystalline thermoplastics such as HPDE, a lower overall deformation is obtained under cyclic stress after the same accumulated stress endurance time that is the case under constant stress. Deformation can be approximated using the linear superposition
principle.
7.8.2 Internal Pipe Pressure
Internal stresses in the pipe wall are created after pipe extrusion as the polyethylene melt is cooled. In this process, it is important to use
an external sizing system for the extruded pipe to remove all the heat outwards. As a result, the outside wall of the pipe freezes while the
inside layer is still molten. With progressive cooling, the material wants to contract inwards but is prevented from doing so by the outer
layer which has already frozen. This forced strain in the inner pipe wall leads to tensile stresses, while compressive stresses are created
in the outer pipe wall.
Excessive internal pipe stresses can be a reason for cracking during storage or transport of the pipe. When a pipe is cut, dimensional
accuracy is impaired because of the release of forced deformation. As a result, the diameter of the pipe end is reduced.
So far, it has not been possible to determine any link between very high internal stresses and creep behaviour. In creep testing, for example with a test temperature of 80°C, the internal stresses are relaxed relatively quickly by annealing. They also relax over a corresponding
length of time at the lower operating temperature in an installed pipeline.
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Graph 7.8 Reference stress for PE100
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Graph 7.9 Creep modulus for PE100
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Graph 7.10 Friction values for plastic pipes (according to Moody)
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Graph 7.11 Acceptable load of underground pipes of PE100 (SDR 33): Proctor density Dpr = 90%, gradient angle ß = 60°
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Graph 7.13 Acceptable load of underground pipes of PE100 (SDR 33): Proctor density Dpr = 90%, gradient angle ß = 90
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Flow nomogram for pressure PE100 pipe system in the SDR series 17 and 11
The areas of validity for the listed flow-rate values correspond with
a flow-medium temperature (water) of 10°C. For deviating operating temperatures, the read values for pressure loss at a corresponding flow-rate amount are to be multiplied by the correction
factor from Table 7.3. The broken lines indicate the upper and lower
limits of the respective pipe dimensions. Given the pipe dimensions
110 x 10mm (SDR 11), the corresponding values are read from
the flow nomogram. To clarify the application limits of our example,
the upper and lower boundaries of the flow capacity are shown as
broken lines.
For instance, the selected pipe dimension de = 110 x 10mm, inside
diameter ds = 90mm and flow-rate volume (V) = 5 l/s produces a
flow velocity (w) 0,8m/s and a pressure loss (p) of 0,7 bar/100m.
Table 7.3 Correction factors for the determination of pressure loss
with corresponding pipe dimensions
Operating temperature (TO) (°C)
Correction factor ( - )
0
1.07
10
1.00
20
0.96
30
0.92
40
0.89
50
0.87
60
0.85
Graph 7.15 Flow nomogram for pressure PE100 pipe system in the SDR series 17 & 11
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Graph 7.16 Maximum operating pressure for PE100 pressure pipe systems
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Graph 7.17 Thermal length change in PE100 pipe systems
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Graph 7.18 Acceptable support distance for water-filled PE100 pipes according to DVS guideline 2210 P1
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Graph 7.21 U-expansion bends
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Graph 7.22 Z-extension bends
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Graph 7.23 Forces at fixed points in axial constricted PE100 pipe systems
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Graph 7.24 Bracket distances in axial constricted PE100 pipe systems
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Graph 7.25 External pressure load or underpressure load of PE100 pipe systems (SDR 17, SDR 11)
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Graph 7.26 Primary times for butt welding of PE100 pipes and fittings
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Table 7.3 Explanation of the applied formulas and abbreviations
Formula sign
V̇
Entity
Explanation
(m /h ; l/s)
Flow volume
V̇'
V̇”
(m3/h)
Flow volume (flow rate)
(l/s)
Flow volume (flow rate)
V̇a
V̇
(m3/h ; l/s)
Outgoing volume (at dividing or uniting flows)
d
(m /h ; l/s)
Total continuous volume (at dividing or uniting flows)
Vs
(m3/h ; l/s)
Total flow volume (at dividing or uniting flows)
Vz
(m /h ; l/s)
Incoming volume (at dividing or uniting flows)
A
(mm2)
Cross-sectional area of flow channel
3
3
3
a
(m/s)
Travelling speed of the pressure surges
A0
(mm2)
Initial cross-section
a0
(m/s)
Speed of sound
A1
(-)
Reduction factor for the influence of the load period
A2
(-)
Reduction factor for the influence of the flow medium
A3
(-)
Reduction factor for the influence of the operating temperature
A4
(-)
Reduction factor for the influence of the specific resilience of the material
aF
(-)
Correction factor for road-traffic loads
Ak
(mm )
Surface subject to pressure
AR
(mm2)
Area of pipe annular surface
C
(-)
Aggregate work factor
2
de
(mm)
Outside diameter of the pipe
DN
(mm)
Nominal diameter of the pipe
di
(mm)
Inside diameter of the pipe
dw
(m)
Thickness of the partition wall
E
(N/mm2)
E-modulus
e
(mm)
Pipe wall thickness
e0
(mm)
Minimum wall thickness
eu
(mm)
Wall thickness on the outside of the bend
EB3
(N/mm2)
E-modulus from 3-point flexural test
EB4
(N/mm )
E-modulus from 4-point flexural test
EcR
(N/mm2)
Elasticity modulus (E-modulus; creep modulus between 1 and 0.10 min); bending
creep modulus
Ec
(N/mm )
E-modulus from the compressive test
EF
(N/mm2)
E-modulus of the flow medium
ei
(mm)
Wall thickness on the inside of the bend
Et
(N/mm2)
E-modulus from the tensile test
2
2
V a l u e
P a r t n e r
hW acc
(m)
Acceptable height of the water column above the top of the pipe
JR
(mm4 ; cm4)
Moment of inertia for the pipe
k
(-)
Heat transition coefficient
KS
(-)
Pressure surge size
l0
(mm)
Initial length
L1,2
(mm)
System lengths
LA
(m)
Bracket distance
LA acc
(m)
Acceptable bracket distance
Lvalves
(m)
Length of valves
LB
(mm)
Length of the expansion bend
LE
(m)
Bracket distance for end pieces
LF
(mm)
Bracket distance
Lfittings
(m)
Length of fittings
LFR acc
(m)
Acceptable load distance
Ltot
(m)
Total pipe length
LK
(mm)
Critical buckling length
Lk acc
(mm)
Acceptable pipe length between two brackets
LM
(mm)
Support distance for the middle of a continuous pipe
Lpipe
(m)
Length of straight pipe components; pipe length between valve mechanism or pump
and reflection position (m)
Moment of torque
M
(Nm)
Mb
(Nm)
Bending moment
MRS
(-)
Minimum strength
pa
(bar)
External pressure, external overpressure
pa tot
(bar)
Pressure difference between external overpressure and internal underpressure
pa max
(bar)
Maximum external overpressure
pabs
(bar)
Absolute pressure
patm
(bar)
Atmospheric pressure
pop
(bar)
Soil stress (acc. to ATV A 127)
pSoil
(kN/m2)
Pump pressure, operating pressure
pE
(kN/m2)
External soil pressure
pF
(kN/m2)
Soil stress due to traffic load (acc. to ATV A 127)
ptot
(bar)
Sum of individual pressure losses
pi
(bar)
Internal pressure
pi max
(bar)
Maximum internal pressure
pi min
(bar)
Minimum internal pressure
pk
(bar)
Critical dent pressure
pkr
(bar)
Critical underpressure
PN
(bar)
Pressure rating, maximum operating pressure
pR
(bar)
Pressure loss in straight pipe sections
pRV
(bar)
Pressure loss in valves
pRF
(bar)
Pressure loss in pipe fittings
F
(N)
Force
fB
(mm)
Deflection
fBo
(-)
Factor for the outside of the bend
fBi
(-)
Factor for the inside of the bend
FFP
(N)
Force at fixed points in a firmly fastened pipe string
FW
(N)
Weight force
FW (fill med)
(N)
Weight force (fill medium weight)
FW (pipe)
(N)
Weight force (pipe weight)
FW (Add load)
(N)
Weight force (additional load weight
Fh
(N)
Axial force component (axial fixed-point force (FFP) or friction force (Fμ) as a result
of a length change in the pipe string)
pw
(bar)
External water pressure
fl
(-)
Long-term welding factor
pw acc
(bar)
Acceptable external water pressure
FLB
(N)
Fixed-point load at (L, Z, U) bends -> Fy c.q. Fx
q
(N/mm2)
Weight of the filled pipe along with any insulation
FQV
(N)
Transverse force
R
(mm)
Bending radius
FR
(N)
Resulting force; resulting load
Re
(-)
Reynolds number
fs
(-)
Short-term welding factor (max. 1h)
Rm
(mm)
Average pipe radius
fst
(-)
Support factors for buried pipe systems
S
(-)
Load-dependent safety factor
pRJ
(bar)
Pressure loss in pipe jointings
pspec
(bar)
Specific welding pressure
psurge
(bar)
Pressure surge
pu
(bar)
Internal underpressure
pu max
(bar)
Maximum internal underpressure
pv
(kN/m2)
Soil stress due to traffic load (acc. to ATV A 127)
FV
(N)
Vertical force
SDR
(-)
Standard dimension ratio
facc
(mm)
Acceptable pipe deflection
SF
(-)
Safety factor = Aggregate pipe coefficient “C”
Fμ
(N)
Friction force
Ta
(°C)
Ambient temperature
h
(m)
Height of the soil layer above the top of the pipe
Ta max
(°C)
Highest ambient temperature
Lowest ambient temperature
Bd
(mm)
Bracket distance
Ta min
(°C)
Hmin
(m)
Minimun soil layer above the pipe
Top
(°C)
Operating temperature
HP
(m)
Delivery height (e.g. pump)
TeR
(°C)
Outer pipe wall temperature
Htr
(mm)
Depth of the trench
Ti
(°C)
Flow medium temperature
Hsl
(mm)
Height of soil layer
Ti max
(°C)
Highest flow-medium temperature
hW
(m)
Height of the water column above the top of the pipe
Ti min
(°C)
Lowest flow-medium temperature
Tcrit
(°C)
Critical operating temperature
tLD
(°C)
Calculated service life
Tm
(°C)
Average installation temperature
281
tR
(s)
Reflection time
ts
(s)
Closing time of the butterfly valve or delay fo the pump stop command after failure
7 DETAILED DESIGN
Y o u r
Table 7.3 Explanation of the applied formulas and abbreviations
(Continued)
Formula sign
V a l u e
P a r t n e r
σϑmax
(N/mm2)
Maximum axial stress due to constricted thermal expansion
ζA
(-)
Sum of the individual resistances of valves, metering equipment, etc.
Sum of the individual resistances of fittings and other components
ζF
(-)
ζRA
(-)
Resistance factors for pipe valves
Inner pipe wall temperature
ζRF
(-)
Resistance factors for pipe fittings
ζRV
(-)
Resistance factors for connections
Entity
Explanation
TsR
(°C)
TW
(°C)
Pipe wall temperature
TW max
(°C)
Maximum pipe wall temperature
TW min
(°C)
Minimum pipe wall temperature
vRF
(-)
Weakening factor of the fitting
Table 7.4 Applied abbreviations
w, wo
(m/s)
Flow velocity
w1
(m/s)
Leak test at the reflection position
Abbreviation
Explanation
WD
(mm)
Distance to wall
ES
Expansion socket
WB
(cm3)
Resistance moment of the pipe
Z
(m)
Lever
(-)
Surge degradation factor
Zs
BZ
Load zone
DZ
Expansion cushion, expansion zone
l
(mm)
Length change
E
Insertion depth
lp
(mm)
Length change due to internal pressure
EFC
Electrofusion coupler
l
(mm)
Thermal length change
GB
Guide bracket
w
(m/s)
Velocity difference
(K)
Temperature difference
FP
Fixed point
FS
Stack trand
SB
Sliding bracket
(K)
Max. temperature difference
σE
(º)
Angle of enlargement
max
σw
(W/m K)
Heat transfer coefficient
GSV
Seat valve
σϑ
(K-1 ; 1/K
;mm/mK)
Thermal linear expansion coefficient
SF
Socket welding
σϑm
(K-1 ; 1/K ;
mm/mK)
Average thermal linear expansion coefficient
HFP
Fixed-point brackets
EF
Electrofusion
β
(K-1 ; 1/K ;mm/
mK)
Cubic (spatial) expansion coefficient)
Expansion
2
BW
Butt welding
K
Size of the bead
Butterfly valve
ε
(-)
ε1
(-)
Expansion of 0.05%
FV
ε2
(-)
Expansion of 0.25%
BV
Ball valve
εF
(-)
Expansion threshold value
MFI
Melt Flow Index
εσx, εσy
(-)
Expansion along the x and y axes of stress in a multiaxial load
γW
(kN/m3)
Specific weight of the fluid
γB
(kN/m3)
Specific weight of the soil
η
(-)
Correction factor
DF
Diaphragm valve
φ
(-)
Shock factor for road-traffic loads
MVI
Melt Volume Index
MVR
Melt volume flow rate
λ
(W/Km)
Heat conductivity
λB
(-)
Bend factor
λR
(-)
Pipe friction number
μ
(-)
Transverse contraction number
MFR
Melt Mass Flow Rate
MRS
Minimum Required Strength
PE
Polyethylene
PE-HD
High density polyethylene
μR
(-)
Friction coefficient
PP
Polypropylene
ν
(m2/s)
Kinematic viscosity
F
(kg/m3)
Density of the flow medium
RFP
Pipe system fixed points
R
(g/cm3)
Density of the pipe material
CV
Clapet valve
CF
Free flow clapet valve
σ
(N/mm2)
Stress
σ0
(N/mm2)
Stress in straight pipe
GV
Gate valve
σ1
(N/mm2)
Normal stress at 0.05% expansion
ISO-S
Pipe series
σ2
(N/mm2)
Normal stress at 0.25% expansion
σ a, σ l
(N/mm2)
Axial stress
SB
Strap
SDR
Standard Dimension Ratio
Angle Seat Valve
σb
(N/mm )
Flexural stress
σB
(N/mm2)
Tensile strength
ASV
σb acc
(N/mm2)
Acceptable flexural stress
TS
Support
σD
(N/mm2)
Compressive stress
VS
Residual deformation
2
σr
(N/mm2)
Radial stress
σR
(N/mm2)
Breaking strength
σres
(N/mm )
σS
(N/mm2)
σt
(N/mm2)
Tangential stress
σu
(N/mm2)
Circumferential stress
σv
(N/mm2)
Reference stress
σx, σy, σz
(N/mm2)
Direction-dependent stress along the x, y and z axes
2
WE
Warmgas Extrusion welding
Resulting stress
WWWN
Warmgas wire welding - normal nozzle
Yield stress
WWWS
Warmgas wire welding - speed nozzle
σZ
(N/mm2)
Tensile stresses
σacc
(N/mm2)
Acceptable stress
σϑ
(N/mm2)
Axial stress due to constricted thermal expansion
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8. LEARN MORE.......................................... 283 - 293
283
V a l u e
P a r t n e r
8 LEARN MORE
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Plastics are used in all areas of our lives and have become indispensable, although most people know little about these materials.
Pipe construction, mechanical engineering and the manufacture of
special parts are increasingly achieved with plastic materials. The
following information about plastics and polymer processing machinery is intended to provide some basic information.
8.1 CLASSIFICATION OF PLASTICS
Plastics are divided into three main groups, Figure 8.1, and Figure
8.2 represents their structures.
Figure 8.1 Classification of plastics into main categories: thermoplastics, thermosets and elastomers
Plastics
Thermoplastics
Amorphous
Thermosets
Elastomers
Semicrystalline
V a l u e
P a r t n e r
8.3 THERMOPLASTICS
Thermoplastics are the most important plastics for pipe construction and the most often used in pipe manufacture is polyolefin, of
which the most important are polyethylene and polypropylene.
They belong to the category of semi-crystalline thermoplastics that
are produced by one of the following processes:
- Polymerisation
- Polyaddition
- Polycondensation
These processes produce various plastics with various properties. In each manufacturing process, there are special procedures
that influence the appearance and characteristics of the specific
plastics. Thermoplastics are further subdivided into two groups:
amorphous and semi-crystalline. Furthermore, plastics are seldom
used in their pure form but usually as mixtures in what are known
as blends or compounds, the composition of which depends on
their purpose and area of application. Blends allow new or altered
characteristics, mechanical, physical or chemical properties to be
created.
However, it is not possible to combine any type of plastic with any
other type; often bonding agents or other additives are needed to
create a bond.
8.2 THERMOSETS AND ELASTOMERS
Thermosets and elastomers play a secondary role in plastic pipe
construction and are therefore only discussed briefly in this manual.
Thermosetting plastics have a close-meshed macro-molecular structure (Figure 8.2) so they are hard, brittle and cannot be
re-melted. Therefore, manufacturers mix the molten mass with fillers that not only "fill", i.e. save material, but primarily add improved
material properties. Areas of application are pipe construction in
plant engineering, fibreglass reinforced containers and flanges.
Elastomers, better known as "vulcanised rubber", are made from
natural or synthetic rubber by an interlinking reaction; vulcanising.
The vulcanising rubber creates a broad-meshed, loose interweaving, which gives the material its typical rubbery qualities under normal conditions. Elastomers are used in pipe construction as seals,
O-rings and flat gaskets between connected elements.
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Figure 8.2 Structural model of thermosets, elastomers and semi-crystalline and amorphous thermoplastics
1.
2.
1 Thermosets
2 Elastomers
3 Semi-crystalline
thermoplastics
4 Amorphous thermoplastics
3.
4.
8.3.1 Amorphous thermoplastics
The arrangement of the molecular bond depends on several factors, particularly the chemical structure of the chain molecule, or
macro-molecular structure. The ordered spatial structure is impeded by long and cumbersome lateral chains and since the molecular
bond occurs in what is perfect disorder, the structure resembles
the structure of a cotton wad. The best known representatives of
the group are:
The degree of crystallisation greatly influences the properties and
transparency of plastic in its natural state. The use of an accelerated cooling rate significantly affects the tendency of the material
to crystallise. Important types of semi-crystalline thermoplastic are:
- polyethylene (PE)
- polypropylene (PP)
- polyoxymethylene (POM)
8.4 CHARACTERISTICS OF AMORPHOUS
AND SEMI-CRYSTALLINE THERMOPLASTICS
- polystyrene (PS)
- polycarbonate (PC)
- polymethyl methacrylate (PMMA; Plexiglas)
- polyvinyl chloride (PVC)
In an uncoloured state, amorphous thermoplastics are as clear as
glass.
8.3.2 Semi-crystalline thermoplastics
Semi-crystalline thermoplastics develop both chemically uniform
and geometrically structured regions (Figure 8.2), which mean
there are regions in which crystals form. Crystals are parallel
groupings of molecular segments or folds in molecular chains.
Therefore, some chain molecules can partly traverse the crystalline
and amorphous regions, or they can belong to several crystallites
at the same time. Semi-crystalline thermoplastics are white. Due to
the dense arrangement of molecules in crystalline bonds, crystallites refract light.
In a comparison of amorphous and semi-crystalline thermoplastics,
there are distinctive properties; the most important are listed below.
In contrast to semi-crystalline thermoplastics, amorphous thermoplastics display:
- greater strength
- greater rigidity
- greater surface hardness
- better surface quality
- less thermal expansion
- less distortion
In contrast to amorphous thermoplastics, semi-crystalline thermoplastics display:
- greater resilience
- less impact sensitivity
- greater flexibility and elasticity
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8.5 PLASTIC PROCESSING MACHINES
V a l u e
Figure 8.4 Layout of an extruder
Plastic processing machines convert raw plastic, mostly in granular
form, into semi-finished products. The following briefly describes
the most important machines and explains their functions and applications, particularly machines that are important in the manufacture of plastic pipes and fittings.
8.5.1 Extruder
Extruders, together with associated dies, cooling units, extractor
units and cutters, are used to manufacture pipes. For improved
quality control, a modern extrusion installation includes connected
inline measuring systems, e.g. wall thickness metres that enable
immediate corrective action to non-conformances during the production process. The operating principle of the extruder involves
melting, i.e. plasticising, raw material and forming it into a new
shape by pressing it through a die followed by a cooling unit.
An extruder (Figure 8.4) may be equipped with one, two or several screws, depending on the material being processed and the
semi-finished product being manufactured; special extruders are
made to suit the needs of the production process. Critical for the
plasticising processes, i.e. the melting of the raw material, are the
screws, the screw geometry and the temperature of the heated
barrels. Due to the shear in the material, it is plasticised at the
necessary barrel temperature; pressure is built up by the extruder
screw geometry and the die, and then transported further along the
screw channels. Three section screws are generally used in standard single-screw extruders, along with barrier screws. The plasticised material is pressed through the die and cooled in a calibration
and cooling unit. The product, e.g. pipe, profile, solid bar, is fixed in
the calibration unit. As a result of this process, the plastic, specifically the macro-molecule chains, is forced into an arrangement and
alignment called "orientation". Extrusion is a continuous process.
Figure 8.3 Principle layout of a pipe extrusion installation
1
2
3
4
Extruder
Die head
Sizer
Water bath
5 Caterpillar
6 Cutting saw
7 Tip unit
286
1 Screw
2 Cylinder
3 Hopper
4 Motor
5 Drive
6 Heater
P a r t n e r
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V a l u e
8.5.2 Injection Moulding Machine
8.6 MECHANICAL PROPERTIES
An injection moulding machine (Figure 8.5) resembles an extruder,
the most important distinction is the motion of the screw which, in
addition to the rotary motion of the extruder, also moves axially.
In contrast to extruders, injection moulding is not a continuous process that makes special demands on the machine, the mould, and
the associated and necessary mould cooling.
8.6.1 Assessing Creep Behaviour
There are three important parameters for the manufacture of an
injection moulded part:
- temperature
- time
- pressure
They have a great impact on the injection moulding process, which
is arranged into three operational steps:
- plasticisation
- injection
- cooling
The plastic to be processed is plasticised while moving along the
screw through the heated barrel; essentially extrusion. The plasticising material is moved forward by the screw towards the screw
tip, simultaneously being pre-compressed. When there is sufficient
material in the "accumulator", which is at the end of the plasticising
unit, the material is squeezed through an injector into the mould. To
prevent shrinkage, plasticised material is compressed for a predetermined time whilst cooling. The machine parameters depend on
the material being processed and the fitting being manufactured. At
the end of the cycle, the process begins again.
P a r t n e r
Creep behaviour is one of the most important characteristics of
plastic pipes and fittings; it indicates the life expectancy of the
product when subjected to pressure which generates stress in the
pipe wall. The reference stress ( r) is based on the relationship of
internal pressure ( i), the safety factor (SF) and the diameter to wall
thickness ratio (SDR). The reference stress ( r) can be calculated
using the well-known boiler formula.
Equation 8.1
acc
i
SDR
S
ref
=
=
=
=
=
Reference stress (N/mm2)
Acceptable stress (N/mm2)
Internal pressure (bar)
Standard Dimension Ratio
Safety factor = General design coefficient "C"
The reference stress ( r) is the stress on the circumference of the
internal pipe surface; the stress in the axial direction of the pipe is
only half the magnitude. The boiler formula provides the acceptable
stress ( acc) of the material which is the basis for dimensioning the
plastic pipe. The stress at break depends predominantly on the
temperature and time of loading.
Figure 8.5 Functional principle of an injection moulding machine
a)
b)
c)
1
2
3
4
5
6
7
8
9
287
The turning screw takes material from the hopper and feeds it along the screw to the tip.
The mould is closed, the injection unit moves against the feed bush, the screw operates as a piston to press plasticised moulding material into the mould.
The cooled injected material drops out of the opened mould, the screw moves new moulding material to the screw tip, the injection unit withdraws from the tip.
Movable mould part
Injection-formed component
Mould cavity
Fixed part of the mould
Nozzle
Heating band
Material cylinder
Screw
Bulk material hopper
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Tests are conducted on water-filled samples of pipe placed in a
bath filled with water at a specified temperature.
Special applications require testing the pipe sections filled with the
intended flow medium. The test results, conducted at various temperatures, are plotted on a log-log graph with the reference stress
plotted against time. The curve in the plot indicates when pipe failure can be expected. Results of the tests at higher temperatures
allows an interpolation of the creep behaviour for a pipe at lower
temperatures which provides the life expectancy of a pipe under
various conditions. The Regression (Creep/Rupture) curves for
PE100 are as shown in reference stress for PE100, see Graph 1.
V a l u e
P a r t n e r
8.6.3 Assessing the elasticity modulus (creep
modulus) Short-term values
The elasticity modulus (E-modulus) is the ratio of stress ( ) to elongation (s):
Equation 8.2
8.6.2 Assessing the Mechanical Variables
In the tensile test (ISO 13953), precisely defined samples are
stretched to breaking point and the required force measured. The
uni-axial load is applied at a prescribed rate and the tensile testing
machine plots the relationship between force and linear extension,
the force/linear extension diagram, which can be converted into a
stress-elongation diagram.
Figure 8.6 Force-linear expansion diagram (tensile force)
= Normal stress at 0.05% elongation (N/mm2)
= Normal stress at 0.25% elongation (N/mm2)
2
= Elongation of 0.05 (%)
1
= Elongation of 0.25 (%)
2
F = Force (N)
A0 = Starting section (mm2)
= Change of length due to force (F) (mm)
l0 = Starting length (mm)
E = E-modulus (N/mm2)
1
Tensile force F in N
ISO 13951 and 2 describe the determination of the E-modulus from
the tensile test (Et), the compressive test (Ed), from the 3-point flexural test (EF3) and the 4-point flexural test (EF4).
Long-term values
The E-modulus under tensile load is determined by means of the
creep tensile test that allows calculation of the creep modulus (EcR).
The tensile test is generally preferred to the flexural or compressive
tests, as it is easier to perform. The test specimen is non-axially
stressed in a controlled test environment by a force that remains
constant throughout the test period. If tests are conducted at the
temperatures of the subsequent application temperature, the diagram provides the engineer with important data to assess the behaviour of the material in service.
Linear expansion l in mm
Curve 1: hard brittle plastic without yield range, e.g. polystyrene (PS)
Curve 2: tough hard plastic, e.g. polyethylene (PE)
Curve 3: flexible elastic plastic, e.g. plasticised polyvynil chloride
(PVC-P)
The diagram shows the following characteristic variables:
- Elongation ( ) - linear expansion ( l) as a percentage of the initial length (l0) at each time interval in the test.
- Tensile strength ( B) - which is the tensile stress at maximum load.
- Breaking strength ( B) - which is the tensile stress at the moment of fracture.
- Yield stress ( Y) - which is the stress at which the increase in the stress-elongation curve is first equal to nil.
The mechanical variables are highly dependent on the test conditions, therefore the test is conducted under carefully controlled
climatic conditions of 23°C and 50% relative humidity. The tensile
test is a short-term test that does not indicate the behaviour of material under long-term mechanical load. Semi-crystalline materials
such as PE and PP display a distinct yield stress and a high degree
of elongation (Figure 8.6).
8.6.4 Impact resistance
The procedures for the impact flexural and notched impact flexural tests are described in the standards which determine impact
behaviour, known as the resilience of the plastic. The variable
measured is the quantity of absorbed impact energy in relation to
the cross-sectional areas that result in fracture of the bar or plate
shaped test specimen, which may be notched. Force is generated
by a pendulum impact tester, which strikes the specimen at high
speed. Two tests (notched and un-notched) are most commonly
performed; "Charpy" and "Izod", and three defined notch types are
used to determine notched impact resistance.
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8.6.5 Surface hardness
8.7.2 Deformation Resistance to Heat
Surface hardness indicates the resistance that a defined specimen displays to being penetrated. The Shore test makes use of
two procedures to determine Shore hardness; known as Shore A
and Shore D. The two procedures differ in the geometry of the test
specimen used; Figure 8.7 shows the two different test needles.
Shore hardness is dimensionless and the hardness varies between
the values of 0 and 100. The Shore A procedure is predominantly
applied to soft plastics, while Shore D is used with hard ones.
All property changes are important to the engineer, especially in
response to temperature. Therefore, various tests are conducted
to ascertain the approximate boundary temperatures below which
deformation does not occur.
In addition to the Shore hardness test, the hardness of a material
can be determined in terms of its ball indentation hardness. This
method is mostly used when the hardness of a material can no
longer be established by the Shore procedure. A ball with a 5mm
diameter is used for the test, which is subjected to a defined load
for 30 seconds.
Figure 8.7 Test objects for Shore A and Shore D hardness tests
Three procedures are used to determine deformation resistance:
1. Martens (DIN 53462)
2. Vicat
3. ISO/R 75 (ASTM D 640)
However, the results do not permit any conclusions to be drawn
about the working temperature of the tested plastics. Values ascertained for plastics are only comparable when they are tested under
identical conditions and procedures. The outside temperature effects of air or fluid as well as the form and manufacturing method of
the samples have a large influence on the results.
8.7.3 Heat Conductivity
The heat conductivity or the heat coefficient ( ), measured as (W/
mK), is a temperature-dependent material characteristic that indicates the capacity of a material to conduct heat. An indication of
heat conductivity or insulation capacity, negative thermal conductivity of a material can be provided by tests specified in ISO 8497.
The heat conductivity of a material can be significantly influenced
by the filling, reinforcements, auxiliary materials, and pigmentation.
8.7.4 Heat Transfer Coefficient
Shore A test needle
The heat transfer coefficient ( ) is an important factor needed to
calculate the heat transition coefficient ( ) as well as specific heat
conductivity (l) of a material. The heat conductivity, like the heat
transfer coefficient, is strongly dependent on other influences, such
as separation plane, geometry and flow rate of the medium.
Shore D test needle
8.7.5 Heat Transition Coefficient
8.7 THERMAL PROPERTIES
8.7.1 Heat Expansion Coefficient
In determining the heat expansion coefficient, a distinction is made
between the linear expansion coefficient, thermal length expansion
coefficient (a ), the cubic expansion coefficient, and the spatial
expansion coefficient ( ). The linear expansion coefficient ( )
indicates the amount a material with a standard length of one metre
will lengthen or shorten under a temperature change of 1o K. The
spatial expansion coefficient ( ) indicates the amount that a cubic metre of material will lengthen or shorten under a temperature
change of 1o K. DIN 53752 describes the tests for the linear and
cubic expansion coefficients. The unit of the expansion coefficient
is (1/K), (K-1) or (mm/mK).
The heat transition coefficient (k) provides information about the
insulation capacity of a material; the unit is (W/m2K). The smaller
the k-value, the higher the insulating capacity of the material. The
heat transition coefficient is computed with the equation:
Equation 8.3
k = Heat transition coefficient ( - )
= Heat transition coefficient of medium 1 to the wall (W/m2K)
w1
= Heat transition coefficient of the wall to medium 2 (W/m2K)
w2
= Heat conductivity of the wall (W/mK)
dw = Thickness of the separation wall (m)
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8.7.6 Burning behaviour
Plastics are organic compounds that are, by their nature, combustible. The European standard EN 13501-1 defines a classification system for material burning behaviour. The burning behaviour of finished products, in the manner that they are used, must be described in
terms of the extent to which the material contributes to the development and spread of fire and smoke in an area or environment. In the
case of fire products are exposed to a fire ignite in a given area. This fire can then grow (increase) and spread. The scenario contains
three components of fires that correspond to the stages in the development of a fire:
- Combustibility: the starting of a fire by ignition using a small flame on a small surface/product.
- Smoke production: development and potential spread of fire.
- Burning drops/fragments: outbreak of fire when all combustible material contributes to the fire potential.
Stage 1: Combustibility
Table 8.1 Combustibility
Class
Fire tests
Spreading of flames
Contribution
Practice
F
Not tested or does not meet class E
Unclassified
Undefined
Extremely combustible
E
EN-ISO 11925-2 (15 sec-Fs<150mm-20 sec)
Spreading of flames 100 kW <2 min.
Very high contribution
Very combustible
D
EN 13823, Figra <750 W/s EN-ISO 11925-2 (30 sec- Fs<150mm-60 sec)
Spreading of flames 100 kW >2 min.
High contribution
Quite combustible
C
EN 13823, Figra <120 W/s + Thr <15 MJEN-ISO
11925-2 (30 sec-Fs<150mm-60 sec)
Spreading of flames 100 kW >10 min.
Large contribution
Combustible
B
EN 13823, Figra <120 W/s + Thr <7.5 MJ EN-ISO
11925-2 (30 sec-Fs<150mm-60 sec)
No spreading of flames
Very limited contribution
Very difficult to combust
A2
EN ISO 1182 of EN-ISO 1716 plus EN 13823,
Figra <120 W/s+ Thr <7,5 MJ
Hardly any contribution
Practically incombustible
A1
EN ISO 1182 = Incombustible EN-ISO 1716 = Caloric values
No contribution
Incombustible
Combustion classification
Level of fire safety in the mines
Stage 2: Smoke production
To supply a product into the mines, the determined and documented
fire behaviour of the product, the comprehensive Risk Assessment
and the vendor’s commitment in terms of Section 21, Manufacturer's and Suppliers Duty for Health and Safety, of the Mine Health
and Safety Act, Act 29 of 1996, must be submitted and approved.
Table 8.2
Class
Description
s3
Great deal of smoke production
s2s
Average smoke production
s1
Little smoke production
8.8 CHEMICAL PROPERTIES
8.8.1 Chemical resistance
Stage 3: Burning drops/ fragments
The chemical resistance of PE in contact with a chemical is dealt
with in detail in Chemical Resistance, Section 3 Engineers.
Table 8.3
Class
8.8.2 Permeation
Description
d2
Fragments burning longer than 10 sec.
d1
Fragments burning shorter than 10 sec.
d0
No production of burning fragments
Fire safety
The required fire safety level of a product is not the same in all environments. Every environment, particularly mining, requires products suitable for the circumstances accompanied by the applicable
Risk Assessment.
Permeation is the diffusion of a medium through a plastic container
wall. Contact between a plastic and chemical medium can, under
certain circumstances, result in moisture expansion or dissolution.
Problems can also result from the dislodging of material by softening and processing agents, as well as from the bleeding of pigmentation. Practical testing procedures are presented in EN-ISO 183;
bleeding of pigmentation.
8.8.3 Water absorption
Although some plastics absorb water and, due to swelling, the dimensional stability changes, PE is water-resilient, which means
that it cannot be damaged by swelling; the test procedure is described in EN-ISO 62.
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8.9 Processing characteristic: Melt
index
3
1
Table 8.4 Test specifications and conditions for determining the
MFR value
2
Test conditions
ISO 1133
Temperature (°C)
1
190
2.16
6
190
10.00
12
230
2.16
18
190
5.00
20
230
5.00
P a r t n e r
Figure 8.8 Stress in the pipe wall
Determination of the melt-mass flow rate (MFR), as specified in ISO
1133, also known as the melt flow index (MFI), is a standardised
testing method for obtaining a relatively quick and quantitative
indication of a plastic's flow behaviour. The MFR value indicates
the amount of thermoplastic molten mass pressed through a standardised orifice in 10 minutes of steady piston force and constant
melt temperature. Table 8.4 indicates the test conditions:
Test specification
V a l u e
4
1 Pipe wall exterior
2 Pipe wall interior
3 D = compressive stress
4 T = tensile stress
Load (kg)
Residual orientation stress
This largely depends on cooling patterns, the speed with which
the orientation in longitudinal and transverse directions is fixed
("frozen-in”), the strength with which heat dissipation acts on both
orientation states raises or lowers the level of orientation, causing
stresses to be increased or decreased.
The unit of the MFR is g/10 min.
8.10 PHYSICS OF PLASTICS
Residual after-pressure stress
8.10.1 Residual stress
All plastic components possess a residual stress, which is due to
manufacturing and cooling conditions. In the extrusion process, the
molten mass is pressed through a die, stretching the macro-molecules, and then it is cooled and fixed in the calibration unit. Because the pipe is cooled from the outside, the pipe wall cools at
different rates which affects the structure and thickness of the pipe.
In the initially cooled outside of the pipe wall, a residual compressive stress (SD) is induced and at the subsequently cooled inside,
a residual tensile stress (ST) (Figure 8.8); these stresses may be
reduced by tempering – reheating the pipe to a defined temperature. The subsequent heating reduces the existing residual stresses, which has substantial effects on dimensional stability, retraction, shrinkage and service life of the pipe. Dimensional stability is
extremely important for pipes and components, since a change in
diameter may have a detrimental affect on leak tightness of connections.
The stresses normally offset each other, but if external or internal
influences cause the stresses to not be in equilibrium, the component may become deformed.
However, the cooling procedure is not the only cause of residual stresses in a plastic component; the following describes other
types of stress that have residual effects on a pipe or fitting.
Residual after-pressure stress mostly occurs in injection moulded
components, although it can also be caused by extrusion processes. For example, an extrusion process is normally used in the manufacture of solid bars, which have to be subject to after-pressure in
order to prevent cavities or bubbles forming. If the pressure during
cooling of fittings is too high, a residual pressure may remain in the
fitting which can lead to distortion.
Residual crystallisation stress
This stress originates in the crystallisation phase of
semi-crystalline thermoplastics. Crystallites that form when the
molten mass is cooling are subject to contraction. Any cooling in an
uneven manner that results in a temporarily irregular crystallisation
process can cause structural strains.
Stress reduction
A remedial measure to abate frozen-in stresses (residual stresses) is the tempering of the pipe. In addition to reducing residual
stress, annealing can instigate an after-crystallisation process in
semi-crystalline plastics, which can have a positive effect on the
properties of plastic.
Annealing is a special temperature control or heat treatment; the
parameters depend on the plastic involved. During annealing, care
must be taken not to heat high enough to generate reset forces and
cause distortion; the parameters depend on the thickness of the
product and the level of stress.
It is important that the products are cooled slowly after storage to
prevent stresses from recurring as a result of local temperature
differences.
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8.10.2 Flexural, Thermal, Tensile and Compres- 8.10.5 Contraction
sive Stresses
These types of stress are discussed in detail in Section 6, as they
represent important criteria in pipe systems construction.
8.10.3 Orientation
The term “Orientation” describes the arrangement of macromolecules in a plastic component.
The macro-molecules of a plastic are initially in a disordered state
– a "knotted ball". The processing, extrusion or injection moulding
forces the macro-molecules through dies, moulds, extractor units
and cooling processes aligning them. They can be arranged both
longitudinally, in extrusion in the direction that the product is extruded, or transversely to the centre line. The nature and alignment
of the orientations have effects on the mechanical properties and
stability of the product; orientation results from shear and expansion forces.
Shear forces are created in both injection moulding and extrusion
processes. They are produced by the shear strain of adjacent strata of molten material flowing at different rates, for example, when
molten material is clinging to the wall of the mould. Expansion forces are caused by the flow of molten material through constrictions
or flow channels, such as nozzles. In extruded semi-finished products, the preferred orientation is longitudinally in the extrusion direction and, less optimally, in the transverse direction. As opposed
to pressed semi-finished products in which no distinct orientation
results, the properties of extruded semi-finished products are
anisotropic; strongly dependent on orientation. Mechanical properties such as strength, impact resistance and impact strength are
better in anisotropic semi-finished products oriented in the direction
of extrusion and poorer in the case of transverse orientation such
as isotropic semi-finished products.
The term “shrinkage” describes a volume contraction of the plastic product. Like other materials, there is a volume increase when
plastic is exposed to a temperature increase.
The cooling of the material initiates the reverse process and this
phenomenon must be considered when manufacturing products
for technically high-grade applications. There are two types of
shrinkage:
- processing shrinkage
- after-shrinkage
8.10.6 Notch effect
The calculation of component stresses is based on tensile and
flexural stresses. However, the stresses that actually occur are
influenced by a number of factors, including inter alia, scratches,
a lack of material homogeneity, and structural composition of the
product, all of which result in deviation from the ideal state. The
size of notches, the radius of notch bases and the types of load
have important effects on the strength of a product. The deeper
and sharper a notch, the higher the stress peak at the notch root
and, consequently, the greater the danger of damage to the component. Therefore, it is advisable to make the shallowest possible
notches which are rounded at the root.
Thermal elasticity is only utilised in temperatures above freezing,
or crystallite melting temperature, so it is not possible to remedy
orientation by annealing.
8.10.4 Retraction
The term "retraction" is the change in the product as a result of
forced length changes of the macro-molecule and occurs especially
in extrusion processes. The molecule is stretched by the extrusion
die and extractor unit, usually in the axial/longitudinal direction. As
soon as the macro-molecule has the opportunity to resume its original shape, a length change counteracts the stretching orientation;
called the "memory effect". Rapid cooling of the molten plastic fixes
it in a “frozen” state and heating the plastic above the "freezing
temperature" activates the "memory effect" and the macro-molecule attempts to return to its original ("knotted") state. Therefore,
retraction is a pure contraction in length as a consequence of orientation of the macro-molecule in the product.
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Table 8.5 Section summary
Plastic
Plastic is divisible into three main groups: thermoplastics, thermosets and elastomers.
Elastomers
Elastomers are better known as rubber. They are wide-meshed, spaciously interlinked synthetic or natural rubber compounds. Interlinking is enhanced by vulcanisation.
Thermosets
Thermosets possess a close-meshed interlinked macro-molecular structure. They are hard, brittle and no longer plasticisable (meltable).
Thermoplastics
Thermoplastics can be divided into amorphous and semi-crystalline thermoplastics.
Polyolefin
This compound belongs to the group of semi-crystalline thermoplastics. Its most important representatives are polyethylene (PE) and polypropylene (PP).
Plastic processing machines
Extruders, injection moulding machines and calendars (not discussed in this manual) are machines used to manufacture plastic semi-finished products.
Extruder
An extruder plasticises raw materials. Used, for example, in the manufacture of pipes, profiles and plates. Continuous process.
Injection moulding machine
Injection moulding involves a discontinuous manufacturing process. The screw performs both a rotational and an axial motion. Important parameters for injection moulding are: temperature,
time and pressure. Process steps are: plasticisation, injection and cooling.
Internal pressure creep test
Simulates the life expectancy of a plastic pipe under an internal pressure load. The associated reference stress ( ref) is a function of the internal pressure, mean pipe diameter and wall
thickness. It is calculated using the boiler formula.
Short-term tensile test
The short-term tensile test involves stretching a sample bar to the breaking point. The result provides an indication of the mechanical values of the tested material. The most important
mechanical values are: expansion, tensile strength, breaking strength and breaking strain. Elasticity modulus (Creep modulus) The elasticity modulus is the ratio of stress to expansion.
Creep tensile test
The creep tensile test is used to determine the creep modulus.
Impact resistance
Impact resistance is determined by means of the impact flexural test and the notched impact flexural test (the latter involving defined notches in the sample). Most important test methods are
the "Charpy" and "Izod" tests.
Surface hardness
Designates the resistance against the penetration of the test specimen. Most important procedures are Shore A, Shore D and ball indentation hardness.
Heat expansion coefficient
The heat expansion coefficient is an important parameter in plastics. A statement of this mechanical value is usually accompanied by an indication of the linear expansion coefficient (aS) (in
literature, this is mostly expressed as the mean linear longitudinal expansion coefficient a).
Heat resistance
This term designates the temperature limits of thermoplastics under the effects of heat. Testing procedures are Martens, Vicat and ISO/R 75. No conclusions about working temperatures are
possible.
Heat conductivity
Variable indicating the capacity of a material to conduct heat. Filling, reinforcements, auxiliary material and colouring affect heat conductivity.
Heat transfer coefficient
This variable is used to calculate the heat transition coefficient. It depends on the separation plane, geometry and flow speed of the medium.
Heat transition coefficient
The heat transition coefficient (k) provides information about the insulating capacity of a material.
Burning behaviour
Plastics are organic compounds and therefore combustible by nature.
Permeation
Diffusion tendency of a material, which is the permeability of fluids or gaseous elements through the plastic.
Water absorption
Many plastics tend to absorb water (swelling). This means that the stability of the plastic is no longer assured. PE has hardly any tendency to absorb water.
Melt index
The melt index indicates the flow capacity of a plasticised plastic. Previously known as the MFI value, it is now referred to as the MFR value.
Residual stress
During an extrusion process, residual stresses build up in pipes as a result of cooling procedures at high extraction speeds, for example. These stresses can be reduced in pipes by adopting
special temperature controls or heat treatments (tempering).
Residual orientation stress
Dependent on cooling conditions. Increasing cooling speed raises the stress potential in pipes.
Residual after-pressure stress
Phenomenon in injection moulding components. Residual after-pressure stress can also occur in extrusion components when, for example, after pressure has to be used in manufacturing
solid bars to prevent bubbles and cavities.
Residual crystallisation stress
This occurs in semi-crystalline plastics (e.g. PE) due to crystallite formation during the cooling phase.
Tempering
Heat treatment to reduce or eliminate residual stress potentials.
Orientation
Alignment of the macro-molecules by external forces (e.g. extraction speed).
Retraction
Retraction designates a longitudinal contraction (negative length change) in the direction in which the macro-molecules are oriented.
Shrinkage
In contrast to retraction, shrinkage designates a volume contraction (negative volume change) as a result of cooling processes. In contrast to retraction, a volume change is discernible in
every plastic component. These volume changes are seen in the fitting structure and in the die or mould structure.
Notch effect
The notch effect affects the strength of the component. Grooves, scratches, in-homogenities or a component's structural form can have adverse affects on the fitting
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9. ABOUT US................................................294 - 296
294
V a l u e
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9 ABOUT US
Y o u r
V a l u e
P a r t n e r
Your TRUE Value Partner
M
arley Pipe Systems is the leading manufacturer and distributor of plastic pipe and fittings for reticulation systems, serving the key market segments of the Building, Civils,
Mining, Irrigation and Industrial sectors throughout sub-Saharan Africa.
We at Marley Pipe Systems are dedicated to serving our clients with quality solutions, expertise, dedication, passion and integrity and,
as an Aliaxis company, we bring solutions, new technology and expertise on a global level to the local market, ensuring our clients are
always ahead of the times. Add to this a commitment to providing only the best in technical support, expertise, integrity and service delivery, and you've got a true Value Partner in Marley Pipe Systems.
Today, the Marley Pipe Systems team consists of over 880 people with the manufacture of all pipe and fittings taking place at Nigel and
Rosslyn in Gauteng.
Vision
To become the preferred and most respected distributor and
manufacturer of quality plastic pipe systems for the Building,
Civils, Mining, Irrigation and Industrial markets in sub-Saharan
Africa.
Purpose
To grow responsibly towards becoming a truly regional
(sub-Saharan Africa) player represented in major centres,
manufacturing fast moving product ranges at local plants
across the region as well as providing a wholesale offering on
group and externally produced products.
Values
• Integrity
• Honesty
• Passion
• Reliability
• Trust
• Accountability
• Compassion
• Professionalism
• Respect
• Commitment
• Excellence
• Ethics
An Aliaxis Company
Aliaxis is the global leader of plastic solutions for fluid handling
systems in residential and commercial markets as well as industrial
and public infrastructure applications. Their focus is on innovation,
quality, excellent service and value, which is reflected in the companies that form the Aliaxis Group. Aliaxis is present in over 40
countries with more than 100 manufacturing and commercial entities, and employs over 14 000 people.
As an Aliaxis Company, Marley Pipe Systems is able to bring reticulation solutions and new technology from around the globe to
the local market in a sustainable manner, focusing on every aspect
of the product lifecycle, from product design and development, all
the way through to recycling of end-of-life waste material back into
new products.
295
9 ABOUT US
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PRODUCTS
V a l u e
Mining
M
arley brings a comprehensive range of plas- • MEGAFLEX Mining Hoses
• Mine-Wall and Metro-Wall Pipe
tic piping solutions to the Building, Civils, • HDPE Pipe Solutions
Mining, Irrigation and Industrial markets. From • Fabricated Fittings
polyvinyl chloride (PVC) pipes and fittings to high • Butt Weld Fittings
• Philmac Compression Fittings
density polyethylene (HDPE) piping systems, all
Marley products are manufactured according to Industrial
the required specifications and go through stringent quality assurance systems and extensive • HDPE Pipe Solutions
testing to ensure that the highest quality standards • Gas Pipe
• Petroplas
are met.
• MEGAFLEX Industrial Hoses
Building
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Underground Systems
Soil & Vent Systems
Waste Systems
Waste Traps
LATCO Pressure Regulating Valves
Marley Equator
Pro-fit Hot & Cold Water Systems
Gutter Systems
Fascia and Barge Boards
Marley Endura Grease Traps
Accessories
Folding Doors
MEGAFLEX Garden Hoses
Compression Fittings
Marley Universal Shower Traps
Civils
•
•
•
•
•
•
•
•
•
Weholite Structured Wall Pipe
PVC Pressure Pipe
HDPE Pipe Solutions
Fabricated Fittings
Marley Electrofusion & Spigot Fittings
Structured Wall Sewer Pipe
REDI Fittings
Gas Pipe and Fittings
Irrigation
•
•
•
•
•
Hydro-Wall & Aqua-Wall Pressure Pipe
HDPE Pipe Solutions
MEGAFLEX Dragline Hoses
Jimten Air Valves
296
MEGAFLEX Suction and Delivery Hoses
P a r t n e r
NOTES
Y o u r
297
www.marleypipesystems.co.za
V a l u e
P a r t n e r
NOTES
Y o u r
298
V a l u e
P a r t n e r
Marley Pipe Systems prides itself in keeping a track record of successful projects
and case studies of work done in the industries it services. To view our Case Studies and Project Successes, please scan the QR code to be directed to
http://www.marleypipesystems.co.za/marley-pipe-news/project-successes
Disclaimer
The information contained within this manual was accurate at the time of print.
Although Marley has made every effort to ensure that the Polyolefin Manual is kept updated and that all information contained therein is as accurate as
possible; the information within the manual is subject to change, and therefore Marley Pipe Systems cannot guarantee its accuracy and completeness
at all times. Users are advised that item specifications and availability are subject to change, without notice, and that Marley reserves the right to retract
items and information at any time.
Marley Pipe Systems does not accept responsibility for any loss, damage or expense resulting from the use of this information.
No part of this manual may be used, reproduced, translated, adapted or converted by any means, or for any purpose, including without limit: sale, resale,
license, rental or lease without the prior written consent of Marley Pipe Systems.
© Copyright Marley Pipe Systems (SA) (Pty) Ltd 2014 | EO&E | Revision 01 | May 2015
Branch Offices:
Bloemfontein: +27 51 434 2331/5
Cape Town: +27 21 980 8460
Durban: +27 31 791 5800
East London: +27 43 726 6505
George: +27 44 874 1160
Jet Park (MEGAFLEX): +27 11 823 1160
Building Head Office
1 Bickley Road,
Pretoriusstad, Nigel
Tel: +27 11 739-8600
Klerksdorp: +27 18 462 2655
Namibia: +264 61 226590
Nelspruit: +27 13 753 2571
Polokwane: +27 15 292 4141
Port Elizabeth: +27 41 045 0998
Port Shepstone: +27 39 682 6212
Witbank (Mining): +27 13 656 1391
Zimbabwe: +263 4 663256
Agents:
Mining & Industrial
Head Office
1 Piet Pretorius Street,
Rosslyn, Pretoria
Tel: 0861 MARLEY (627539)
Contract Supplies (Botswana): +267 392 2922
RJ Rogers (Namibia): +264 612 37201

6 construction - Marley Pipe Systems

Transcription

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