Why SPO flanges are so superior to ASME flanges

Transcription

Why SPO flanges are so
superior to ASME flanges
regarding risk of leakage
Tor Eriksen
Freudenberg Oil & Gas
Technologies
Copyright © 2013 Freudenberg Oil & Gas Technologies
SPO® Compact Flange
Why Leaks ?
1. Unauthorised opening when pressurised
0
+
3. Misalignment and insufficient sealing pressure ( low gasket factor)
N/A
4. Misalignment/excessive bolt preload and sealing pressure – gasket damage
N/A
5. Fatigue damage/ detoriation of seal from vibration
N/A
2. Insufficient bolt preload (final tightening forgotten by reopening after testing)
6. Fatigue damage/ detoriation of seal from variabel piping displacements due to
temperature variations or external distortions e.g. hogging and sagging in floating
structures
N/A
Slide 2
Why Leaks ?
+
8. Fatigue crack in bolts
N/A
9. Fatigue crack on flange material
N/A
10. Bolt relaxation from loads as outlined in paragraphs 5 and 6 above N/A
11. Failure of threaded joint between bolts and nuts
+
12. Failure from inappropriate material quality in bolting, flanges or seals +
7. Corrosion
Slide 3
Why Leaks ?
1.
Unauthorised opening when pressurised
0
+
N/A
4. Misalignment/excessive bolt preload and sealing pressure – gasket damage
N/A
5. Fatigue damage/ detoriation of seal from vibration
N/A
6. Fatigue damage/ detoriation of seal from variabel piping displacements due
to
structures
N/A
Slide 4
Unauthorized opening when pressurised
How?
Most frequent:
Mix-up of equal branch connections to a manifold.
Misunderstanding / poor communication, not by purpose
Does not happen at flange joints,
which are not connected to valves,
equipment, maintenance spools or
blinds, e.g. in flanged joints along
this flare header of the NORNE FPSO.
The IX seal ring would start with a small leak during disassembly, thus
providing a warning whistle before a hazardous leak would occur. Such prewarning cannot be guaranteed for most of the gaskets used in ASME flanges.
Slide 5
Unauthorized opening when pressurised
Mix-up and opening of any pressurised
type of bolted joint may happen in a
manifold system, but the compact flange
offers other benefits here:
Well-bays
• Typically large number of flanges and
valves, high pressure
• Frequently modified offshore - new
wells on stream
• Large number of leak sources
Compact Flanges for well-bays offers
•
•
•
Space saving – often critical in these areas
Significant weight savings
Improved safety and environmental
conditions due to gas tight, leak free and
maintenance free connections
Slide 6
Why Leaks ?
1. Unauthorised opening when pressurised
0
+
N/A
Misalignment/excessive bolt preload and sealing pressure – gasket damage
N/A
Fatigue damage/ detoriation of seal from vibration
N/A
4.
5.
6. Fatigue damage/ detoriation of seal from variabel piping displacements due
to
structures
N/A
Slide 7
Insufficient bolt preload
• It cannot be revealed by visual inspection if the bolts of an ASME flange connection
have been tightened properly or if nuts have been finger tightened, only
•
Leaks from ASME flange joints at start up due to forgotten bolt tightening are
highly represented in statistics on causes to leakage from flange joints
• If compact flanges are closed with no visual gap between the flanges at the outer
rim, there must be a lot of preload from the bolting. (At least 2/3 of required
preload is then applied to a SPO CF joint)
Slide 8
Why Leaks ?
+
N/A
N/A
+
7. Corrosion
Slide 9
Corrosion
Most leaks from corrosion will start slowly including all bolted joints.
ASME flanges
with flat sheet gaskets may release large amounts of fluid suddenly due
to gasket rupture when flange sealing areas get corroded, and result of
this is bolt relaxation.
ASME RTJ flanges
may also start leaking suddenly from breakdown of a corroded seal ring.
SPO CF
The double barrier of the SPO CF makes corrosion to the seal ring virtually
impossible. Even if micro scratches on the heel surfaces hasled fluid
pressure to the seal ring, the supply of corrosive fluid would be extremely
low.
The seal ring of the SPO CF is much better protected against external
corrosion than any seal or gasket suitable for ASME flanges.
Slide 10
Why Leaks ?
+
N/A
N/A
+
7. Corrosion
Slide 11
Failure of threaded joint between bolts and nuts
• Warping of large ASME flanges is frequent when tightening the bolts.
Result is high stress on the first threads in the bolt to nut connection
because the nut will impose severe bending stresses to the bolt when
flange surface is not perpendicular to the bolt axis.
• The SPO CF is designed so that bending of bolts is impossible.
• Dynamics in ASME flanged connections provides high risk of fatigue
cracks at high local stress areas in the bolts.
• SPO CF provides no dynamic load to the bolt and nut connections.
• High fire loads may cause failure of bolt and nut connections in flanged
connections before bolt relaxation will result into a leak.
• The SPO CF can be protected from this scenario by simply using special fire
nuts, while corresponding fire protection of an ASME flanged connection would
require insulation of the complete assembly.
Slide 12
Why Leaks ?
7. Corrosion
10. Bolt relaxation from loads as outlined in paragraphs 5 and 6 above
+
N/A
N/A
N/A
+
12. Failure from inappropriate material quality in bolting, flanges
or seals
+
Slide 13
Failure from inappropriate materials
•
Failure from inappropriate materials in flanges, bolting
and seals is less likely when no component is subject to
dynamic loads.
• Forgings for machining of SPO flanges and seal rings
are subject to the most stringent requirements.
• Bolting materials shall satisfy the latest requirements in
ASME VIII Div. 2
Slide 14
Leak limit comparisonExample 6” class 1500
• A 6” class 1500 bolted RTJ to ASME
B16.5 shall be typically tightened to a total
load of 1704 kN
• This gives an extra theoretical capacity of
512 kN axial load or 27kNm bending
moment without leakage if flanges have
infinite stiffness, i.e. no deformation! Both
FEA and testing show severe
deformations>>>>>>
• The corresponding class 1500 compact
flange joint shall be tightened to a total
load of 2316 kN.
• This gives an extra capacity of at least
275 kN axial force or more than 18kNm
bending moment for the tightness of the
heel seal based on 1,5 x DP (ref. ISO
27509, clause 4.2)
Slide 15
Leak limit comparisonExample 6” class 1500
• In a test performed by DNV in 2003 on a 6” class
1500 CF to NORSOK L-005 in 316SS, the heel
seal kept tight until a tension load of 750 kN and
with an internal pressure of 258,6 bar.
• This corresponds with an equivalent pressure of
550 bar. The tension force was then increased to
1975 kN until yield of bolting and pipe, but the
joint was still tight!
Tension and Pressure test of 6”
class 1500 CFC in 316SS, Oct.
2003
Slide 16
Risk level welded versus flanged joint
• Statoil and several other oil companies do not permit welding outside
pressurized habitats in process areas during production on offshore
platforms.
• A DNV study for Statoil in 2005 concluded that habitat welding during
production represent a risk to potential loss of life (PLL) of same magnitude
as the precence of a standard ASME flange joint in service for 20 years.
• The SPO CF will significantly reduce risk of leakage, and thus reduce the
PLL compared with ASME flanges as explained in this presentation.
• Report no/DNV Reg No.: / 12FQG2F-6, Rev 01, 2010-03-12,”Reliability
Evaluation of SPO Compact Flange system” concludes that leak probability
from the bolted joint itself may be less than from the adjoining girth welds to
the pipe.
Slide 17
Reliability acc. to DNV report of March 2010
Leakage rate per year of a flange connection compared to piping and girth weld
Slide 18
Bolt load versus pressure
Bolt
Load
(all
together)
Typical curve for a large ASME flange connection
IX seal is pressure energized when heel
faces are not sealing any more
Sufficient to seal?
SPO CF joint
ASME flange joint
Pressure
Slide 19
Fugitive emissions - Examples
The most stringent requirements to fugitive
emissions have been met:
• A 16₺ class 2500 SPO CF joint with IX seal ring was qualified to
Shell MESC SPE 77/312*) leakage class A at 431 barg and
120oC in February 2011.
• An 8₺ 15,000psi SPO CF joint with HX seal ring was qualified to
Shell MESC SPE 77/312*) leakage class A at 1035 barg and
ambient temperature in Oct. 2011. (Test recordings were
lower than limit of reliable readings according to the Shell
specification)
*) The accumulation technique in accordance with EN 1779, B3, as referenced in
Shell MESC SPE 77/312 of August 2010, was used.
Slide 20

Why SPO flanges are so superior to ASME flanges

Transcription

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