Titanium Alloys – How to Capitalize on the Performance in

Titanium Alloys – How to Capitalize on the Performance in
Demanding Corrosive Applications While Assuring Against Failure
Richard A. Clapp
Senior Consultant – Materials Engineering
DuPont Engineering Technology
John A. Mountford Jr.
Director of Marketing
Tico Titanium, Inc.
Presented at:
2001
Chem Show
the 49th CPI Expo - Javits Convention Center, New York City
October 23 - 25, 2001
Introduction:
Titanium alloys along with their reactive metal brethren can provide significant advantages over the more
historically specified nickel base and high alloy stainless steels in corrosive chemical process
environments.
The downside of titanium is that misapplication, faulty design or operation of equipment outside the
anticipated process conditions can lead to unacceptable equipment failure. This risk can be
inconsequential when a structured approach is applied to the selection process, when proper equipment
design practices are employed and cooperation between the process and operations communities
assures that process conditions stay within prescribed limits of safe alloy performance.
This paper is complementary to the 2001 Chem Show Conference Program presentation, that focuses on
some of the key considerations that one needs to take with respect to specification, equipment design,
and maintenance of titanium process equipment to assure long-term trouble free performance. In the oral
presentation the focus is on the structured approach to be applied for alloy selection, from a corrosion
standpoint, and the required operational control that history has shown can translate into decades of
trouble and maintenance free service.
TITANIUM SPECIFICATIONS FOR ALLOYS USED IN THE CPI
Fortunately for the consumer, the titanium industry has wisely chosen to produce to ASTM specifications
and not create a dearth of company specific specialty alloys. Where new alloys have been developed, as
has been the case with the recent addition of the lean Palladium and Ruthenium doped alloys, the
company developing the alloy quickly moved for inclusion into the ASTM product specifications.
Appendix I provides details of the different ASTM designated grades that have application in the CPI
along with a brief thumbnail sketch of the typical applications and their chemical compositions. [Fig. 1
contains the actual chemistry compositions of the grades.] This write-up is very beneficial in
understanding the different alloy grades, that are essentially identical in mechanical properties, but which
differ only by the small quantities of Palladium and Ruthenium added for improved corrosion resistance.
Appendix II racks up the various product specifications and related specifications [listed in Fig. 2] for
titanium alloys used in the CPI. It also provides a listing of sizes available in industry for the various
product forms. It is included to provide a handy reference for the reader.
Appendix III provides the details regarding the Welding and Other Fabrication Processes utilized for
titanium.
ASTM and the associated ASME product standards are quite complete and don’t require supplemental
company specifications for the bulk of CPI applications. Some of the standards have supplemental
requirements that can be specified, but these should only be selected when a real benefit can be
identified.
The ASTM specification for condenser and heat exchanger tubing, B 338 is a case in point. It is a very
comprehensive specification. The required nondestructive testing is often only available as supplemental
requirements for nickel and stainless alloys or it requires independent specification. For example, welded
titanium is subjected to an electromagnetic (eddy current) and an ultrasonic test. In addition, a hydrostatic
or pneumatic test is also required. Except for high-pressure applications, practice is to conduct a
pneumatic test, which provides high sensitivity to very small defects that aren’t picked up by the
electromagnetic (EC) or ultrasonic (UT) techniques.
DESIGN CONSIDERATIONS
The successful design of process equipment using titanium alloys is a mature science. Titanium
equipment has been utilized in the chemical industry in significant quantities for well over 30 years. Key
properties of titanium, however, influence the specifics of the design. Outlined below are some
experience-based considerations when designing with titanium.
Thermal Expansion
The significantly lower thermal expansion of titanium versus competitor nickel and stainless alloys doesn’t
pose a problem in initial design if recognized, but historically it has caused problems because it was not
considered during component or equipment replacement. Key areas where thermal expansion
considerations need to be taken into account are:
•
Shell and Tube Heat Exchangers – In new design typically no problems are encountered if
proper expansion calculations are conducted as part of the design process. For re-tubed
exchangers, analysis should be conducted to assure that the existing expansion joint is
adequate for the new shell and tube material combination. Special care needs to be taken when
re-tubing exchangers with tubes and shells of the same material, as changing to titanium can
result in tube end loads that exceed the pullout strength of the expanded joint.
2
•
Vessel Replacement – Piping stress analysis should be conducted on mating piping to assure
that no excessive nozzle loads are applied due to piping moments, or due to differential thermal
growth between the vessel and piping
•
Use of titanium for vessel internals, such as distillation trays and packing supports in nickel and
stainless steel alloy vessels, mandates the need to take into account the significant difference in
thermal growth between titanium and the shell materials. Locking of components to the shell,
and not providing points where relative motion can occur has resulted in failures of titanium
internals and failures of vessel shells at the attachment points.
Modulus of Elasticity
Shell and Tube Heat Exchangers – One common reason for the failure of titanium tubed exchangers is
vibration damage. This typically manifests itself as tubing wear at the baffles but also can result in wear
due to tube collision and in rare cases, local hydriding of tubes in the contact areas. This problem is often
encountered when titanium exchangers are ordered as replacements of existing units without an
experienced design review.
•
Thermal rating programs such as “HTRI” (Heat Transfer Research Institute) have built in analysis
routines to determine if vibration is a concern when designing new equipment. It should also be
considered as an assessment tool when replacing “in kind”, except for materials.
•
Very conservative practice is to minimize the free span of titanium tubing to no greater than 30”.
Note that this is NOT BAFFLE SPACING, as tubes in the area of the baffle that don’t overlap
adjacent baffles are supported only be every other baffle.
•
Double and triple segmental baffles have often been utilized to reduce potential titanium tube
vibration problems when conventional single pass designs are shown to be inadequate owing to
the high shell-side flow rate.
•
Increased baffle thickness reduces contact loads under vibration conditions, reducing the wear on
the tube. Baffle thickness should not be skimped on.
•
Where process is on the tubeside, it is good practice to standardize on 304 baffles, tie-rods and
spacers in cooling water and steam applications. This assures that the baffle to tube fit doesn’t
increase with corrosion of the baffle hole, which can lead to vibration. It also provides protection
against local hydriding that has infrequently occurred when a process leak into the shell has
caused rapid corrosion of carbon steel baffles.
•
In some exchanger layouts, the edge of the baffles can be scalloped and not fully confine a tube
on all sides. This can lead to the tubing being supported in only one direction. Under the proper
excitation, these tubes on the scalloped edge can fail by baffle wear, even though the free span
of the tubing is within correct limits.
Thermal Conductivity
Thermal conductivity of titanium is significantly lower than copper and copper-nickel alloys, but 50%
greater than 304 SS. On the other hand, titanium has excellent antifouling characteristics in the full
range of industrial cooling waters, from fresh potable water to seawater. Thin tube gauges can be
specified with titanium because no corrosion allowance needs to be specified. Also, titanium has
excellent erosion-corrosion resistance in cooling waters versus competitor alloys such that cooling
water velocities can be much higher than competitor alloys. All these, combined, lead to titanium
often being significantly more thermally efficient than the other alloys.
3
•
Take advantage of titanium’s antifouling behavior when selecting the fouling coefficients for
exchanger design. Proper selection can result in significant exchanger area reductions and lower
exchanger cost versus other alloys.
•
Take advantage of titanium’s resistance to erosion /corrosion by maximizing cooling water
velocities consistent with pressure drop constraints and potential for tube vibration. Rules such as
3 to 6 feet per second for cooling water on the tube-side need not apply.
•
Often, in the design process for new facilities, heat exchanger sizing will be done for cost
estimating purposes prior to final materials selection; or sizing will be based on a base material
and the design will be sent out for pricing with titanium as one of the material options. To assure
the most cost effective design is achieved, exchangers should be thermally rated and sized with
titanium taking credit for the low fouling, thinner tube gauges and higher permissible velocity
characteristics.
Material Strength
Design stresses for the CP alloys drop significantly with temperature. This, combined with the low elastic
modulus (see “Vacuum Design”), will often require a thicker vessel than that of an alternate material.
Design allowable stresses for titanium per the ASME code are shown in Table 1.
•
Decisions should be based on fabricated cost! To the uninitiated, the greater required
thickness for titanium indicates higher cost. In reality, titanium is very competitive versus other
alloys in first time costs. Table 2 provides some cost comparisons to provide a sense of the
relative costs. As alloy prices are constantly changing, pricing of titanium and other candidate
alloys should be obtained for comparison by requesting budget quotations from fabricators and
suppliers. A key mistake seen in past projects is to estimate the equipment thicknesses for
another candidate alloy, take the calculated weight, and then price the vessel on a “per lb” cost
3
3
for titanium. With titanium’s low density of 0.163 lbs./in versus 0.294 lbs./in for stainless steel,
the use of this method greatly overestimates titanium material costs.
•
Process people often don’t appreciate the impact of selecting a high design temperature for
equipment. They routinely set vessel design temperatures equivalent to the supply pressure for
steam used in steam-out. In reality, these temperatures are not reached as the steam supply is
small and the vessels are typically at atmospheric temperature during the process. Significant
savings in fabricated cost can often be achieved by mechanical and process interaction to set the
vessel design temperature as low as practical.
Vacuum Design
In most critical vessel applications, full vacuum is a design criteria. This allows for the ability to handle
product draining and steam out conditions without the use of vacuum breakers or other elaborate (and
often failure prone) systems to minimize negative pressure in the equipment. With titanium’s low elastic
modulus, vacuum can be controlled at lower pressures than can competitor alloys.
•
Where vacuum is controlling in design, resistance can be improved by increasing the thickness or
the use of external stiffeners on equipment. In most cases the more economical choice is to use
more stiffeners. Typical practice is to use plate ring stiffeners and not complex shapes such as
tees or angles. This will typically result in the stiffeners projecting through the insulation. Titanium
is immune to stress corrosion cracking under thermal insulation so that elaborate “boxing in” with
insulation of the stiffeners is only required where significant concerns for heat losses due to wet
insulation exist.
4
•
Temperature has a strong effect on vacuum resistance. As noted above for positive pressures,
the selection of the design temperature under full vacuum should be specified as low as possible.
If the conditions where vacuum can occur are at a distinctly lower temperature than for positive
pressure, two design conditions can be specified to capitalize on the differences.
Flange Design
Details of flange types used in titanium equipment are covered below in the piping section. One
consideration that should be addressed in flange design is the potential for crevice corrosion. Gasket
surfaces on titanium equipment can suffer crevice corrosion in high temperature brines and halogenated
high temperature organic acid environments. Where crevice corrosion has been identified or, in new
processes where the risks of crevice attack are not fully assessed, gasket surfaces have been produced
from the more crevice resistant materials such as Grade 7. They have been produced for stub-ends by
welding a crevice corrosion resistant titanium grade to a Grade 2 barrel or by making the complete stubend from the crevice corrosion resistant grade. For clad equipment a similar process has been used for
producing nozzle and nozzle liners.
Internal Vessel Attachments
Titanium internals such as baffles, agitator paddles and feed and dip pipes have experienced failures in
operation due to fatigue. Titanium has the advantage over other alloys in that its fatigue strength is not
materially effected in most corrosive environments. Its very low corrosion rate allows for successful weld
contouring and blending that can provide benefits over the life of the equipment.
Care should be taken to properly support piping inside the vessel. A good practice is to mechanically
restrict piping and baffles against vibration by craddling them in supports with guides, without directly
welding them to the supports, where vibration is a serious concern.
Most titanium agitators are of bolted construction with the paddles attached to the shaft by bolting to allow
for removal through manways and agitator openings. Typically the paddle and agitator are mated together
with a flange type arrangement, with bolting going through the paddle and paddle flange. It is very
important that the mating surfaces of the flange be flat and that the back of the flanges be spot faced or
machined to assure that those surfaces are parallel to the mating surfaces. This should be checked as
part of any critical titanium agitator final inspection after fabrication. If these surfaces are not parallel then
the proper bolt pre-load can be lost in service leading to premature failure of the bolting. This is an item
that can also be overlooked when repairs are done to paddles due to cracking of attachment welds in the
vicinity of the flange.
Piping Design Considerations
Titanium piping offers a very cost effective and reliable solution in many corrosion applications. Key
considerations with piping systems are:
•
Grade 2 titanium is the most common piping used in chemical processing. Grades 3 and 12 have
also been specified for specialized applications to a limited degree. Piping and components, such
as elbows and tees, are readily available. One area that can impact the cost of titanium piping
systems is in the specification of titanium cast valves. Cast Titanium valves can be expensive
versus competitive alloys (see Table 3). Use of valves fabricated completely from wrought
components and ‘Wafer” style valves should be considered as options to cast style valves. Fully
lined Teflon valves have also been used quite successfully as a lower cost option to cast titanium.
5
•
Welded pipe is readily available and of high quality. Applications are limited where the benefits of
seamless product out-weigh the additional cost. In some borderline services such as hot pure
nitric acid, titanium welds can corrode faster than the base metal. Specification of seamless
product can increase the life to some extent in these services.
•
Schedule 10 is typically specified in the chemical process industry. Owing to the very low
corrosion rate exhibited by titanium, the use of schedule 40 for additional corrosion allowance is
not required. Certain specific cases where erosion plays a role or in high-pressure applications,
schedule 40 is specified. Schedule 5 has also been specified in applications owing to the cost
advantage of the thinner wall thicknesses. It should be noted that irrespective of material,
Schedule 5, especially in the smaller diameters, requires skilled welders to successfully weld.
•
Standard flange design for titanium equipment is lap joint stub-ends or studding pads of solid
titanium. Stub-ends are typically fabricated from plate versus being forged. Fatigue of titanium
stub-ends has occurred around pumps, compressors and centrifuges and areas of flashing two
phase flow, where significant piping vibration has existed. For areas where fatigue may be
anticipated, Type A stub-ends with fully finished welds between lap and barrel can provide
significant added benefit with respect to fatigue.
Owing to the strength and elastic modulus of titanium, titanium slip-on flanges and solid weld
neck construction are seldom used. (If this style flange is considered, remember that detailed
flange design is required using the ASME rules to determine required design thicknesses.)
In industry, backer flanges from carbon steel to high alloy have been specified. Often, the impact
of the selection of the backer flange material is overlooked. With a flange leak, carbon steel can
corrode quite rapidly resulting in having to cut off the stub-end to replace the flange or, in some
cases, reinforcing with a split ring back-up flange is possible. Galvanized steel is not
recommended for the same reason. In addition, if galvanized material is smeared onto the
titanium by the flange, it can potentially lead to hydrogen embrittlement. The most cost-effective
selection from a life cycle basis is typically 304 or 316 SS. In the overall cost of a titanium vessel,
back-up flanges are typically a very small cost and, considering the maintenance costs
associated with repair, should not be selected strictly on a first cost basis.
•
When changing piping in a system from another alloy to titanium the following should be
considered:
Titanium being of lower elastic modulus can have piping strain focused on it from the
higher modulus piping. A qualified individual should conduct a piping flexibility analysis
when piping is changed to titanium.
Two phase, flashing flow and high process circulation rates that didn’t excite the original
piping may excite titanium when installed. Always have a knowledgeable piping engineer
inspect the line after it is put into service.
FABRICATION
Titanium fabrication of chemical process equipment is a mature industry. The bulk of fabrication is of solid
construction. Explosion bonded titanium to carbon steel for clad construction is a proven technology used
in high pressure applications where the significantly lower cost of the carbon steel results in lower asfabricated costs. Although carbon steel is by far the most common backer material, titanium clad on
stainless steel is sometimes used for tubesheets to protect against backer corrosion in very aggressive
environments should a failure of the titanium occur.
6
Welding
Welding is the most commonly raised concern for titanium fabrications. It is true that special attention to
joint cleanliness and proper gas shielding techniques are required to assure that welds are not embrittled
or reduced in corrosion resistance. The major manufacturers, however, have long perfected these
shielding techniques. Welding both in an open shop environment and for field welding repairs is routine.
In reality, titanium welds very easily with good flowability and wetting of joint surfaces. From the welder’s
perspective it is much easier to weld than many of the nickel based and stainless alloys. Detailed
considerations for welding are included in Appendix III.
MAINTENANCE CONSIDERATIONS
Clad Equipment – Purge Holes
In clad vessels, batten straps of titanium are used to bridge the welded joints of the backer steel.
Typically, the backer steel is welded out and ground smooth, a filler compatible with titanium is inserted in
the joint to bring the surface flush with the surrounding clad surface and then a piece of titanium that
bridges the joint is added and fillet welded to the clad surface on each side of the joint. To assure against
oxidation of the back side of the batten strap welds, purge holes are added. These are drilled through the
backer to allow the flow of purge gas through the joint, typically with a _ coupling welded to the outside
over the hole to allow for attachment of the purge fitting.
Care and feeding of these purge holes is critical to assure that if a leak does occur through the cladding
repairs are minimized. Once put into service, these purge holes can be very effective tell-tale holes to let
one quickly know whether the batten straps have either been breached by corrosion or fatigue. Always
add piping extensions on the nipples and extend them outside of the insulation. Also include, as part of a
normal patrol of the equipment, having operations inspect the purge holes for leakage. When extending
them outside of the insulation, be sure to have a screen on the end of the pipe to assure that inspectors
don’t get in and plug the hole. If you leave them buried in the insulation, leaks can go on for an extended
period. Considering that in many services the corrosion rate of bare carbon steel in the process can
exceed 5 inches per year or more!, early detection can be critical.
Don’t try and get fancy with these purge holes. Several large pieces of equipment suffered life-long
reliability problems with batten strap failures because they initially ganged all the purge holes together
and pulled a vacuum through a detector trying to identify the first onset of leakage. Unfortunately, when a
leak occurred, the process material migrated from purge hole to purge hole contaminating behind all the
batten straps in the vessels. If the purge holes had not been interconnected, only one local area would
have had to be addressed.
•
A historical concern in some companies and in specific processes has been that of iron being
smeared onto titanium during maintenance activities, leading to pitting in various chemical services.
This has lead to practices such as only allowing aluminum scaffolding in vessels, requiring disposable
boot coverings when entering vessels, lining vessel floors to assure against tools contacting the
titanium, and ferroxyl or other test methods to assure no surface iron contamination is present after
completion of maintenance. In laboratory tests it has not been possible to produce pitting without
embedding iron in the titanium and having a cap of titanium over top to make a very tight crevice.
This is very difficult and the very low number of failures that can be attributed to embedded iron in
industrial practice supports this.
The requirement for the extent of required precautions is debated in the industry. The actual practices
employed should be selected with analysis of the process chemistry and the risk of attack. For example,
many services are inventoried with cold acid that will effectively pickle the iron from the surface prior to
raising equipment temperatures, while in oxidizing non-halide environments the risk of embedded iron
causing damage to the titanium is extremely remote.
7
Painting Near Titanium Equipment
Titanium requires no external painting for protection. Titanium is not subject to corrosion under wet
insulation. Caution should be taken when spraying structural steel or other equipment in the vicinity of
titanium equipment. Failures have occurred when inorganic zinc primer has been inadvertently sprayed
on to titanium surfaces. With the inorganic zinc present, corrosion of the paint can occur with acid
leakage on to the painted surface resulting in hydrogen generation and hydrogen embrittlement of the
titanium.
Titanium Cleaning
Heat Exchangers – High Pressure Water Cleaning
Tubeside cleaning of titanium exchangers with high-pressure water is done routinely. Titanium or Ni-CrMo nozzle tips are specified in some cases where iron contamination of tubing is a concern. Titanium is
resistant to high-pressure water erosion, but the minimum required pressure for cleaning should always
be specified. Some specifications limit the pressure in critical, severely plugged tubes. Where ultra-high
pressure cleaning is the only viable method, it is good practice to determine the dwell time to cause
damage.
This is done using the proposed cleaning procedure and equipment, and running trials by holding the
lance in a trial tube at one location and recording the time to perforation. The test is then conducted at
fractions of the perforation time and the tube is split open to see what dwell time causes damage to the
tube. This gives a good indication of the relative dwell time that can be tolerated during cleaning without
damage.
Heat Exchangers - Chemical Cleaning
Typical practice in some facilities is to chemically clean the cooling water side of all heat exchangers on a
set frequency independent of the specific exchangers’ heat transfer performance. Titanium exchangers
with their low fouling characteristics often will not require cleaning at the same frequency as others, if at
all. Good practice is to not require chemical cleaning of titanium exchangers unless clear thermal
performance degradation is documented and other cleaning methods are not suitable.
It is critical that when chemical cleaning will be conducted on titanium exchangers that the chemical
cleaning contractor has demonstrated experience with cleaning titanium equipment and that information
is clearly transmitted to the contractor that titanium will be cleaned. This is more of a concern when a
large number of exchangers are to be cleaned on a shutdown and include an individual titanium
exchanger.
Major failures of titanium equipment have occurred due to cleaning operations where HCl was utilized
without sufficient oxidizing inhibitors. Ammonium bifluoride (ABF) which when added to HCL promotes
silica scale removal, has been responsible for severe attack due to the generation on hydrofluoric acid.
TABLE 1
8
Allowable Stress Values Per Section VIII of the
ASME Boiler and Pressure Vessel Code
Material
ASTM
Form and
Grade
Spec. No.
Sheet
Strip
Plate
SB-265
1
2
3
7
12
9
Specified
Tensile
Strength
For Metal Temperature Not Exceeding Deg. F
(Design Stress in KSI)
Min.
Yield
0.2%
Offset 100
35.0
50.0
65.0
50.0
70.0
90.0
25.0
40.0
55.0
40.0
50.0
70.0
150 200 250 300 350 400 450 500 550 600
8.8
12.5
16.3
12.5
17.5
22.5
8.1
12.0
15.6
12.0
17.5
22.5
7.3
10.9
14.3
10.9
16.4
21.7
6.5
9.9
13.0
9.9
15.2
20.8
5.8
9.0
11.7
9.0
14.2
19.8
5.2
8.4
10.4
8.4
13.3
8.6
4.8
7.7
9.3
7.7
12.5
17.6
4.5
7.2
8.3
7.2
11.9
16.8
4.1
6.6
7.5
6.6
11.4
15.8
3.6
6.2
6.7
6.2
--15.3
Source: 1998 ASME Boiler & Pressure Vessel Code, Section II – Part D
TABLE 2
Cost Comparisons for CPI Equipment
Fabricated from Titanium and Other Corrosion Resistant Grades
Material
Cost Comparison
Vessels
Heat Exchangers
Ti Grade 2
1.0
1.0
Ti Grade 7
1.3
1.3
Ti Grade 12
1.05
1.1
Incoloy 825*
1.1
1.1
Zr Grade 702
1.3
1.4
Hastelloy B-2**
1.6
1.6
Hastelloy C-276**
1.5
1.6
*Registered Trademark of INCO
**Registered Trademark of Haynes International
Source: International Titanium Association [ITA] website www.titanium.org (Ti Information Section)
TABLE 3
9
3.1
5.7
6.0
5.7
--15.1
Relative Cost of Titanium
Versus
Other Corrosion Resistant Cast Plug Valves
Valve
Size
Titanium
CD-4Mcu
Alloy 20
Hastelloy C
2”
10.7
1.3
1.3
5.7
4”
7.9
1
1.2
5.5
6”
9.1
1.1
1.2
6.1
*Registered Trademark of Haynes International
10
*
APPENDIX I
TITANIUM GRADES AND TYPICAL APPLICATIONS
This section provides a thumbnail synopsis of available grades of titanium that are utilized in chemical
process environments.
Commercially Pure Grades
Grades 1, 2, 3 (and 4) represent the original Commercially Pure (CP) grades.
Residuals - Oxygen, Iron, Carbon, Nitrogen & Hydrogen impart the strength levels.
•
•
Carbon, Oxygen and Nitrogen act as interstitial strengtheners, maintaining a single-phase hexagonal
close packed “alpha” microstructure.
Iron & Hydrogen act as second phase body-centered cubic “beta” grain refiners - offering moderate
strengthening capabilities.
Grade 1:
The CP grade with the lowest residual content makes it the lowest strength CP grade with the highest
ductility & excellent cold formability. (Typically 99.8% Ti)
Applications: “Deep pressing” and intricate forming of sheet strip and plate for Plate & Frame Heat
Exchangers (PFHE). It is also used as the corrosion resistant titanium layer of “explosive –
bonded” Clad plates for liners in tubesheets, pressure vessels, columns, tanks and chemical
process equipment, for transition joints and parts or equipment not requiring high strength
but of a more complex shape.
Grade 2:
The “workhorse” of the CP grades and most widely used in industrial service, it has a good balance of
strength and ductility with strength levels very similar to those of common stainless steels and with
ductility that allows for good cold formability. (Typically 99.6% Ti)
Applications: Pressure Vessels, Columns, Pipe (welded & seamless), Tubing (primarily welded &
seamless) in Shell & Tube Heat Exchangers & Utility Steam Condensers, Tubesheets,
Fittings, Fasteners, Flanges, Valve Bodies, Rod, Wire, etc.
Grade 3:
A slightly higher strength grade due to its higher oxygen & nitrogen residual contents, with somewhat
lower ductility. (Typically 99.4% Ti)
Applications: Tube Sheets (for stronger joints) and for Pressure Vessels, etc., where thinner walls can be
accommodated, due to its higher intrinsic strength.
Grade 4:
Highest strength CP grade used mainly in the aerospace/aircraft industry, which because of its high
strength levels and lower ductility is not commonly seen in the CPI.
Applications: Anodizing Racks and Baskets for a variety of industrial metal anodizing applications.
Grade 12
Developed (slightly alloyed) for moderately higher crevice corrosion resistance at high temperatures
(500º - 550º F, 260º - 288º C) and lower pH levels (to as low as 2.5 – 3) having the benefit of higher
strength but with a moderate reduction in ductility.
Applications: Pressure Vessels and other Chemical Process Equipment that can be designed with
thinner walls in lower pH and/or higher temperature service and where crevice corrosion is
11
a factor. Used in Salt Evaporators in the production of salt, in Brine Condensers, Refinery
Crude Overhead Condensers and as Heat Exchangers using salt water cooling at elevated
temperature levels.
Grade 9:
An alloy grade 3 Al – 2.5 V (also referred to as half 6Al–4V) is significantly stronger with an approximate
75% increase in yield strength above that of Grade 2, harder, with good erosion resistance, finding a fair
amount of use in CPI applications.
Applications:
Pressure Vessels (allowing thinner gauges), Autoclaves, Shafts & Impellers.
Grade 5
A very high strength alloy (6Al – 4V), 3 times that of Grade 2 with very high erosion resistance and
hardness.
Applications: Shafts & Impellers (in Autoclaves), Rotating parts, Centrifuges and Turbine components.
Grade 23
An alloy (6Al – 4V ELI [extra low interstitials]) with very high strength levels, slightly lower than that of
Grade 5, developed for use where strength levels close to those of Grade 5 would be required but where
Stress Corrosion Cracking (SCC) would be a factor.
Palladium & Ruthenium Doped Alloys
These alloys have small amounts of palladium or ruthenium added, which dramatically improves
titanium’s resistance to reducing acid conditions and crevice corrosion.
Elemental Ruthenium is considerably less expensive than elemental Palladium which is why it is used as
a substitute (for economic reasons). Grade 26 is cheaper than Grade 7, but can be lower, equivalent or
slightly higher than Grade 16 in cost, dependent upon Ru and Pd prices which continue to fluctuate. This
is true for all the grades with a Ru addition.
Grade 1 Mechanical Property Equivalents
Grades 11 & 17 [Palladium]
These alloys correspond to Grade 1 in mechanical properties. They were developed for their resistance
0
0
0
to severe crevice corrosion areas in brine/chloride solutions for temperatures to 500 – 550 F (260 –
0
288 C) and pH levels to as low as 1 (or under) at these higher temperatures. They also allow for the use
of titanium in more reducing acid conditions. Grade 17 is the leaner Pd version, more economical, but
with the same resistance as Grade 11, except for some specific applications.
Grade 27 [Ruthenium]
This alloy was developed to replace Pd for lower cost and added availability. The same parameters apply
as those for Grades 11 & 17.
Applications:
These grades have the identical physical & mechanical properties as Grade 1 and are
used in similar applications where high temperature and/or low pH crevice corrosion
situations exist or where reducing conditions warrant their use.
12
Grade 2 Mechanical Property Equivalents
Grades 7 & 16 [Palladium]
These alloys correspond to Grade 2 in mechanical properties. They were developed for their resistance
0
0
0
to severe crevice corrosion areas in brine/chloride solutions for temperatures to 500 – 550 F (260 –
0
288 C) and pH levels to as low as 1 (or under) at these higher temperatures. They also allow for the use
of titanium in more reducing acid conditions. Grade 16 is the leaner Pd version, more economical, but
with the same resistance as Grade 7, except for some specific applications.
Grade 26 [Ruthenium]
This alloy was developed to replace Pd for lower cost and added availability. The same parameters apply
as those for Grades 7 & 16.
Applications: These grades have the identical physical & mechanical properties as Grade 2 and are
used in similar applications where high temperature and/or low pH crevice corrosion situations exist.
Grade 9 Mechanical Property Equivalents
Grade 18 [Palladium]
The equivalent of Grade 9 in physical & mechanical properties but with Pd to impart a high level of
corrosion resistance at higher temperatures and/or very low pH levels. Also, it significantly reduces the
potential for stress corrosion cracking in specific environments.
Grade 28 [Ruthenium]
The equivalent of Grade 9 in physical & mechanical properties but with Ru to impart a high level of
corrosion resistance at higher temperature and/or very low pH levels.
Grade 5 Mechanical Property Equivalents
Grade 24 [Palladium]
The equivalent of Grade 5 in physical & mechanical properties but with Pd to impart a high level of
corrosion resistance at higher temperatures and/or very low pH levels.
Grade 29 [Ruthenium]
The equivalent of Grade 23 in physical & mechanical properties but with Ru to impart a high level of
corrosion resistance at high temperatures and/or very low pH levels.
13
Chemical Compositions of Titanium Grades Used in the CPI
ASTM
UNS
N
C
H
Fe
O
Grade
Number
max
max
max
max
max
Al
V
Mo
Ni
Pd
Ru
each
max
1
R50250
0.03
0.08
0.015
0.20
0.18
0.10
0.40
Bal
11
R52550
0.03
0.08
0.015
0.20
0.18
0.12 - 0.25
0.10
0.40
Bal
17
R52252
0.03
0.08
0.015
0.20
0.18
0.04 - 0.08
0.10
0.40
Bal
27
R52254
0.03
0.08
0.015
0.20
0.18
0.10
0.40
Bal
2
R50400
0.03
0.08
0.015
0.30
0.25
0.10
0.40
Bal
7
R52400
0.03
0.08
0.015
0.30
0.25
0.12 - 0.25
0.10
0.40
Bal
16
R52402
0.03
0.08
0.015
0.30
0.25
0.04 - 0.08
0.10
0.40
Bal
26
R52404
0.03
0.08
0.015
0.30
0.25
0.10
0.40
Bal
3
R50550
0.05
0.08
0.015
0.30
0.35
0.10
0.40
Bal
12
R53400
0.03
0.08
0.015
0.30
0.25
0.10
0.40
Bal
9
R56320
0.03
0.08
0.015
0.25
0.15
2.5 - 3.5
2.0 - 3.0
0.10
0.40
Bal
18
R56322
0.03
0.08
0.015
0.25
0.15
2.5 - 3.5
2.0 - 3.0
0.10
0.40
Bal
28
R56323
0.03
0.08
0.015
0.25
0.15
2.5 - 3.5
2.0 - 3.0
0.10
0.40
Bal
5
R56400
0.05
0.08
0.015
0.40
0.20
5.5 - 6.5
3.5 - 4.5
0.10
0.40
Bal
23
R56402
0.03
0.08
0.013
0.25
0.13
5.5 - 6.5
3.5 - 4.5
0.10
0.40
Bal
24
R56405
0.05
0.08
0.015
0.40
0.20
5.5 - 6.75
3.5 - 4.5
0.10
0.40
Bal
29
R56404
0.03
0.08
0.015
0.25
0.13
5.5 - 6.75
3.5 - 4.5
0.10
0.40
Bal
0.08 - 0.14
0.08 - 0.14
0.2 - 0.4
FIGURE 1
0.6 - 0.9
0.04 - 0.08
0.08 - 0.14
0.04 - 0.08
0.08 - 0.14
Other Other
Ti
APPENDIX II
Titanium Product Specifications
BAR / BILLET / FORGINGS
ASTM
ASME
Titanium and Titanium Alloy
Bars and Billets
B 348
SB 348
Titanium and Titanium Alloy
Forgings
B 381
SB 381
PIPE
ASTM
ASME
Titanium and Titanium Alloy
Welded Pipe
B 862
Code Case
Replaced ASTM B 337
Titanium and Titanium Alloy
Seamless Pipe
B 861
Code Case
(Now Discontinued)
B 36.10M
Dimensions only
Welded and Seamless
Wrought Steel Pipe
Stainless Steel Pipe
MSS
COMMENTS
ASME / ANSI
MSS
COMMENTS
B36.19M
TUBING
Seamless and Welded Titanium
and Titanium Alloy Tubes for
Condensers and Heat
Exchangers
ASTM
ASME
B 338
SB 338
FLANGES / FITTINGS
ASTM
ASME
Seamless and Welded Unalloyed
Titanium and Titanium Alloy
Welding Fittings
B 363
SB 363
Pipe Flanges & Flanged Fittings
Dimensions only
ASME / ANSI
MSS
COMMENTS
ASME / ANSI
MSS
COMMENTS
B 16.5
Steel Pipeline Flanges
Factory - Made Wrought
Steel Buttwelding Fittings
ASME / ANSI
Dimensions only
SP - 44
B 16.9
Wrought Stainless Steel
Butt - Welding Fittings
Dimensions only
Dimensions only
SP - 43
Dimensions only
Forged Fittings, Socket Welding and Threaded
B 16.11
Dimensions only
Ferrous Pipe Plugs, Bushings,
and Locknuts with Pipe Threads
B 16.14
Dimensions only
Wrought Steel Buttwelding Short
Radius Elbows and Returns
B 16.28
Dimensions only
Steel Line Blanks
B 16.48
Dimensions only
15
Titanium Product Specifications cont'd
STRIP / SHEET / PLATE
ASTM
ASME
Titanium and Titanium Alloy
Strip / Sheet / Plate
B 265
SB 265
CASTINGS
ASTM
ASME
Titanium and Titanium Alloy
Castings
B 367
SB 367
WIRE
ASTM
ASME
Titanium and Titanium Alloy
Wire
B 863
SB 863
TESTING & CLEANING
ASTM
ASME
Ultrasonic Examination of Metal
Pipe and Tubing
E 213
Electromagnetic (Eddy Current)
Examination of Seamless and
Welded Tubular Products,
Austenitic Stainless Steel
and Sinilar Alloys
B 426
Descaling and Cleaning
Titanium and Titanium Alloy
Surfaces
B 600
ASME / ANSI
MSS
COMMENTS
ASME / ANSI
MSS
COMMENTS
ASME / ANSI
MSS
COMMENTS
ASME / ANSI
MSS
COMMENTS
ASTM - American Society for Testing & Materials
ASME - American Society of Mechanical Engineers
ANSI - American National Standards Institute [a Division of ASME]
MSS - Manufacturers Standardization Society
FIGURE 2
16
PRODUCTS (Sizes, Descriptions & Comments)
Plate:
• Thickness - 3/16” [0.1875”] through 10” Most common sizes 3/16” through 1-1/4”. Heavy sizes in
the range of 2” – 3-1/2’’ are common for Tube Sheets (high-pressure) applications.
• Width
- 96” as produced (most common); can be made to 170” wide. Outside USA 60” wide
(1.5 meters) is the most common.
• Length
- 240” standard but can be made to 400” (depending on thickness)
Sheet:
• Thickness - 0.016” min., generally, 0.020” to under 3/16” (0.1875”). Most common to 0.120”
• Width
- 48” standard. Outside USA 39.4” (1 meter) is common. Can be cut to any width above
24” (the minimum to be defined as sheet).
• Length
- To 20 ‘ (240”). Most common is 120”
Strip:
• Thickness - 0.016” min. generally, 0.020” to under 3/16” (0.1875”). Common to 0.100”
• Width
- to 24” max. Outside USA 39.4” (1 meter) is common. Can be cut to any width below 24”
(the maximum to be defined as strip).
• Length
- To 20’ (240”) cut lengths. In coils - to hundreds (thousands) of ft (based on gauge).
Pipe:
• All standard diameter Nominal Pipe Sizes (NPS) and Schedule sizes (thickness) are available.
• Diameters from 1/8” through 30” (welded & seamless) Sch 5 & Sch 10 to 12” diameter for Sch 40 &
Sch 80. Most common are the Sch 10 walls.
• Due to its high strength/weight ratio Sch 5 can be used for economy and weight reduction.
• Welded pipe is more economical and much more common than seamless pipe in industrial
applications, as in the CPI.
• Titanium is highly erosion/corrosion resistant and ideal for salt water cooling.
• Weight savings of 34% to over 85% (versus stainless steels, copper nickel and other Nickel Base
Alloys [NBA]) can be attained since its density is 56% of steel and 50% of Cu and Ni alloys. The Sch
wall thickness and Nominal OD’s can also be reduced in many applications using higher flow rates.
Tube:
• Most common for Industrial applications (i.e. heat exchangers) are the “Process Tube” sizes –
20 gauge - 3/4” x .035” and 1” x .035” and 18 gauge - 3/4” x .049” and 1” x .049” [OD x Wall]
• Very high erosion/corrosion resistance, elimination of corrosion allowance in saltwater, brines,
polluted waters, etc. make savings possible by using reduced wall thicknesses.
• Millions of feet of welded process tubing are produced annually and it is significantly less expensive
than seamless tube by a factor of 2 to 2-1/2 times (sometimes more, depending on the actual tube
size). These sizes are very common and are stocked.
• For condenser heat exchangers, particularly for the Utility industry, 25 gauge - .020” is generally the
thinnest wall, with 22 gauge .028” the heaviest. Diameters of 1” are generally the largest and most
common. Multi millions of feet are produced annually for this service.
• There are 3 NDT tests performed on welded tubes – Ultrasonic, Eddy Current, Hydrostatic or
Pneumatic that assure the intrinsic high quality standards of the product.
Fasteners: [Screws, Nuts, Bolts, Washers, etc.]
Fittings: [Elbows, Tees, Stub Ends, Reducers, Couplings, Weld-O-Lets, Soc-O-Lets, Thread-O-Lets]
Flanges: [Slip-On, Weld Neck, Blind, Threaded, Figure 8 Blanks, Spectacle Blinds, etc.]
Specialty parts are also available.
17
APPENDIX III
WELDING & OTHER FABRICATION PROCESSES
CP & 6Al – 4V are the most common grades of titanium that are welded. Most welding is done outside of
a chamber and it is relatively easy to get very good welds. By Cladding (Explosive welding) titanium can
be joined to other metals.
Tungsten Inert Gas (TIG) / Gas Tungsten Arc Welding (GTAW) is the most common method of welding
titanium. However, all methods can be successfully used, including all of the following:
Gas Metal Arc Welding (GMAW) / Metal Inert Gas (MIG); Plasma Arc Welding (PAW); Electron Beam
Welding (EBW); Laser Beam Welding (LBW); Resistance Spot / Seam Welding (SPOT); Flash Welding
(FW); Explosion Welding (EW); Submerged Arc Welding (SAW); Diffusion Bonding (DB) and Brazing.
TIG/GTAW fusion welding is a mature technology, extremely common and performed by thousands of
welders. Trained welders have no problems welding complex equipment. Typically, A TIG welder (of other
metals) can be qualified on titanium within 2 weeks (within a week, in many cases).
0
Trailing shield of Argon is required to allow Ti to cool below 700 F to prevent oxidation.
For CP titanium, due to its purity, the weld pools are very fluid, are much easier to weld and preferred by
trained TIG/ GTAW welders over many alloys (i.e. stainless and nickel base).
MIG / GMAW is generally used to weld material > 1/8” (The thicker the metal the more economical)
Weld gas required is Grade 4.5 [99.995% pure …50 ppm impurities]
Filler metal to AWS specification A5.16
SHOP PRACTICES
Cleaning
0
Titanium must be Free of dirt, oil, moisture and dust (heat to 160 F to remove moisture)
Use non-chlorinated solvents such as acetone, MEK or alcohols (No Methanol)
Wipe joint area then Brush with new stainless steel wire brush 1/2” to 1” back from the joint
Wipe again with acetone and wipe the filler rod
Use (no lint) white cotton gloves
Area should be clean and free of drafts
Tight joint fit up (to minimize air) and overlap starts
Purging
Torch should contain a large diameter cup with a diffuser and a trailing shield
Use non-permeable gas hoses
Trailing shield should have a separate gas line
0
Back side purge tooling used if back is above 500 F
Pre-purge setup before striking arc
0
Post-purge until Ti is below approx. 700 F
Verify weld color & parameters on a scrap piece (for comparisons)
Testing
Liquid Dye Penetrant (Easier for Ti due to the fluidity of the weld)
Radiographic
Visual
Hardness / Scratch
Color – an additional check (see below)
18
Color & Weld Quality
Weld color is an indication something was not 100% correct but may not mean the weld is bad. It may
only be that the trailing shield was not kept above the weld long enough and some oxidation occurred and
may only be a surface condition. Straw and light blue is generally acceptable in many applications.
Once past the Light Blue stage, in most cases, the weld should be ground out / checked to determine if it
is throughout the weld or a surface condition and appropriate corrections in weld technique should be
made.
Coloration is an indicator of the thickness of the oxide layer. The table [Edison Welding Institute] below
indicates the progression of oxidation and its effect on Elongation. The fact that titanium shows different
colors is a plus, in that it presents an addition visual process control test.
Base
Glossy Silver
Light Straw
Dark Straw
Light Blue
Purple
Dark Blue
Dull Yellow
Dull Gray
Powder White
30 % Tensile Elongation
20 % Elongation
“
12 % Elongation
“
“
< 12% Elongation
“
“
“
OTHER FABRICATION PROCESSES
Titanium is not an exotic material and is most often fabricated on the same equipment as other materials
such as stainless steels and nickel base alloys. Taking into account the differences in its metal properties
such as a lower density and much lower modulus of elasticity, higher melting point, lower ductility, etc.
and compensating for them is the key to successful fabrication. Some items with respect to titanium
fabrication are shown below:
Shearing
Capacity standards similar to type 300 stainless steel
Cutting – Practically all methods
Oxy-Acetylene Torch – same gas, smaller tips, higher speeds
Plasma Torch - option
Abrasive Saw – Rubber bonded 60 grit silicon carbide wheels are common
Hacksawing – coarse blades (3,4, or 6), lots of coolant to minimize heat, heavy feeds
Band Sawing – coarse pitch teeth (6 per in. recommended); high-speed steel blades I” wide are typical;
2
cutting rates about 1 in /min; water soluble or sulfo-chlorinated coolant & rigid setup.
Grinding
Hand Abrasive Grinding – Use Large grain, open type, and clean wheels; avoid heat buildup; Do Not use
sandpaper or steel wool; protect areas from sparks; avoid collecting grinding dust.
Wheel Grinding – hard wheel, vitrified bonded is best; Al2O3 good below 2000 surface ft/min; SiC @
4000 to 6000 surface ft/min; feeds of 0.001” per pass common; grit of 60 to 80 and
hardness of J to L are common; complete flooding best.
Belt Grinding – 5 to 10 micro inches are possible; SiC resin bonded cloth generally best; 50 grit for coarse
& 120 grit for fine grinds; lots of fluids, 1000 to 2000 sf/min and 100 psi load generally best.
19
Machining
Not difficult, similar to Austenitic stainless steels. Use Low speeds, maintain high feed rates, lots of
coolant, sharp tools, do not stop feeding while tool and work are in contact and use rigid setups.
Machinability Index for CP Titanium is 40 [302 Stainless = 35; 1020 Steel = 70; 2017 Al = 300]
Turning
Milling
Boring
Tapping
Reaming
Gear Hobbing
Drilling
Broaching
Shaving
Planing
Shaping
Forming
Readily formable @ RT using same equipment, etc. as for steel. Ductility being less, more generous
Bend Radii are needed.
Hot forming may be necessary for severe bends (there is more spring-back due to the modulus of
elasticity being half that of steel). Lubrication is very important.
Source; Information in Appendix III – International Titanium Association [ITA] (Broomfield, CO) “The
Fundamentals of Titanium:101” and Hi-Tech Welding Service, Inc. (El Cajon, CA)
20