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A New Grade for Titanium
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 October 2006 Feature
James A. McMaster is the principal of MC Consulting, specializing in titanium application and business development. Typical projects include studies solving manufacturing problems, project management, to market development. McMaster has authored or co-authored over 40 papers. He is active in ASTM International, ASME International, the American Welding Society, and ASM International in areas of interest to producers and users of titanium.

Barry Greene is an associate director of the Materials Technology Institute. MTI is a not-for-profit organization that provides leadership in materials technology, enabling the chemical processing industry to improve reliability, profitability, and safety. Greene has also held senior materials engineering positions at BASF and ABB Lummus, and has authored or co-authored a dozen papers. He is also active in NACE International and ASM International.

A New Grade for Titanium

Many ASTM International material specifications were written decades ago. While these specifications have evolved, the specified minimum properties have rarely been revisited since they were first established. In the interim, the industry has invested millions of dollars upgrading capabilities to produce a better and more consistent product. In some cases, these advances may justify revising the mechanical, chemical, or other requirements of corresponding ASTM specifications.

An example of such an activity is the recent addition of the “H grades” to the ASTM titanium specifications by ASTM Committee B10 on Reactive and Refractory Metals and Alloys.

This paper discusses:

• The background leading to this particular change,
• How the traditional role of producers in property development was replaced by a user group that saw an economic advantage in the change,
• The importance of the ASTM committee consensus process, and
• A summary of the expected benefits.

Background

The 40- to 50-year-old data used to develop current ASTM titanium properties may no longer represent modern material. Changes in production practice have resulted in more consistent material chemistry with reduced levels of residual elements whose combined effect is not fully understood. Producers have learned to control titanium ingot chemistry so accurately that their ability to achieve consistent results and variation in properties is vastly improved from when the ASTM titanium specification property values were first established.

A 1998 review of approximately 250 Grade 2 titanium test reports found that all reported ultimate tensile strength, or UTS, values exceeded 60 ksi (410 MPa), well above the 50 ksi (345 MPa) specification minimum. The results were presented to titanium producers with a proposal that if this were true in a substantially larger sample, the industry might produce a competitive advantage for titanium by simply changing the minimum specified UTS to reflect what was routinely being achieved in practice.1,2 Since the American Society of Mechanical Engineers’ Code Design Allowable Stresses for titanium are controlled by the minimum UTS, a significant savings in equipment cost could be realized if higher allowable stresses based on a higher minimum specified UTS could be utilized. Because the ASME code is used as the basis for a wide range of industrial equipment, the effect of such a change would be significant.

Role of the Materials Technology Institute

The Materials Technology Institute, headquartered in St. Louis, Mo., is an organization of over 50 member companies, many of which use, fabricate, or manufacture titanium or titanium equipment. MTI representatives include decision-making personnel from many of the world’s largest companies in the chemical and petrochemical industry. Each year MTI sponsors research projects that have a significant benefit to the members’ materials engineering efforts.

MTI member company representatives quickly saw that an increase
in the minimum specified tensile strength would lead to reductions in the cost of equipment they procure every year. In addition, MTI’s membership and reputation brought prestige to the project that was important in getting cooperation from producers on a worldwide basis as well as getting recognition of the importance of the project by ASTM International, ASME International, and other standards developing organizations.

The larger study, begun in 2002 and jointly sponsored by the Materials Technology Institute, the International Titanium Association, and MC Consulting,3 included data from over 30 producers worldwide, and over 8,000 data points. These data showed that over 99.5 percent of the Grade 2 unalloyed titanium in a database of 5,280 tests had a UTS significantly higher than the minimum 50 ksi (345 MPa) in the existing specifications, while covering the full range of yield strength, as shown in Figure 1. The study also showed that the unalloyed titanium Grades 1, 3, and 4 wrought-mill products also have similarly higher UTS values than indicated by current ASTM and ASME specifications.

Project Objectives

Grade 2 titanium is widely used in the industrial corrosion sector and has become a de facto standard grade for most applications. This singular focus has allowed the relatively small titanium industry to offer a wide range of mill products and sizes, often from stock. Retaining that focus was a key objective of the project.

Objectives are summarized as follows:

• Take advantage of higher minimum UTS in ASME Code and related construction.
• Maintain the standardization on Grade 2 for industrial and general applications.
• Maintain the availability of full range of titanium products resulting from effective standardization on Grade 2 for most industrial and general applications.
• Minimize any tendency for producers to change the current ingot chemistry formulations (i.e., increasing the oxygen or iron content to be more certain of making the higher tensile strength).
• Determine if changes in other unalloyed grades, i.e., Grades 1, 3 and 4 were warranted.

Proposal to Change Minimum UTS in ASTM Titanium Specifications

The project resulted in a proposal to ASTM Committee B10 to change the minimum UTS of not only Grade 2, but also of the other three unalloyed titanium grades. This met with surprising resistance. However, the process to resolve the issues is a clear demonstration that the ASTM consensus process can produce a better result. Some of the concerns brought up by stakeholders are listed below.

• There was concern that additional restrictions in the specification requirements would lead to unnecessary product rejections even though the control of chemistry required to meet the proposed strength appeared to be easily within the normal capability of the ingot producers.
• Some producers thought that overall consumption of titanium would decrease due to reduced thickness requirements.
• There was a belief that a change in minimum UTS would cause the producers to reformulate their materials to meet the higher properties, giving up some ductility and fabricability important to users of Grade 2 even though the data showed that material above a specific oxygen level always met the 58 ksi (400 MPa) requirement and only material that had a low oxygen level (comparable to Grade 1) that was applied as Grade 2 fell below 58 ksi (400 MPa).
• ASTM Committee F04 on Medical and Surgical Materials and Devices, which develops standards involving titanium for medical devices, known as the “F specifications,” was concerned about any changes in basic specified properties because the regulatory process they face to recognize such a change is long and costly. While the F specifications specify the affected properties independently, this was still a factor in not wanting to change the minimum property levels in the existing B (Committee B10) grades. (The F specification grade requirements generally follow the grades in the B specifications.)

The committee concluded that there was no commercial incentive to increasing the UTS of Grade 1 since it is primarily used for explosion cladding or plate heat exchanger applications where maximum ductility is required and for chlorine anode substrates where higher electrical conductivity is also desirable. Committee B10 recognized that this need could be better served by reducing the minimum specified yield strength of Grade 1 to a level close to the lowest in the data base, which has the same effect on the ratio of minimum UTS:YS of increasing the UTS of Grade 2. This was accompanied by adding a supplemental requirement limiting the maximum yield strength to 40 (275 MPa) instead of 45 ksi (310 MPa). The committee suggested reviewing this situation in five years to see if a general shift in production would justify making the 40 ksi (275 MPa) upper limit mandatory.

The committee also concluded that there was little interest in changing the minimum UTS of Grade 3 because it is less widely used for pressure equipment than Grade 2, even though the data showed it could be done. Also, about 30 percent of the material (in the database) that could be dual certified as Grade 2 and 3 at existing Grade 3 minimum tensile strength would not meet the proposed higher UTS.

Finally, the committee concluded that there was no reason to change Grade 4 because it is not listed in the ASME Code.

As a result, no changes were approved by the committee for Grade 3 or 4.

The H Grades

To be responsive to the user interest represented by the MTI study, and to address the concerns expressed, ASTM Subcommittee B10.01 on Titanium developed a consensus to add the 58 ksi (400 MPa) material as a separate grade, but linked it to the standard Grade 2 by assigning it a readily associated Grade 2H designation.

Grade 2H can always be dual-certified as Grade 2, and in nearly all cases, Grade 2 will meet the requirements of Grade 2H. Since the standard numeric grades have been retained, it is expected that ingot producers will have minimal incentive to change their melt formulations. Retaining the standard numeric grades also addresses the medical application concerns where the qualification of changes in material is costly. The nomenclature “Grade 2H” is readily associated with “Grade 2,” minimizing the need to separately establish the H grades as a market standard.

These changes were incorporated in the 2006a revision of the wrought titanium material specifications. H Grade counterparts 7H, 16H, and 26H for the corrosion enhanced Grades 7 (Ti-0.12Pd), 16 (Ti 0.06Pd), and 26 (Ti 0.1Ru) were also added to the specifications.

Estimated Impact of the Higher Strength Levels

It is difficult to estimate exactly how much this change will save industrial users each year. The 16 percent increase to 58 ksi (400 MPa) from 50 ksi (345 MPa) minimum tensile strength and the corresponding increase of design-allowable stress in ASME is expected to reduce equipment cost by an average of 10-16 percent, assuming labor and material have equivalent cost. The market for affected equipment was estimated to be of the order of $100 million. Thus, if the 58 ksi (400 MPa) grades were fully implemented into pressure equipment, the annual savings could be as high as $16 million, year after year.

Finally, the higher strength addresses the current shortage in titanium by reducing the amount of material required for a specific vessel. However, use of the H Grades is expected to result in more applications where titanium is competitive, and over time a net increase in usage will result. //

(See the sidebar "Benefits of New Titanium Specs" here.)

References

1 McMaster, James A., “Is it Time to Modernize the ASTM Specifications for Unalloyed Titanium,” presented at the “Titanium, Its Role, Its Growth and Its Applications in the CPI” session, 49th CPI Exposition, Javits Convention Center, New York, New York, October 23-25, 2001
2 McMaster, James A., “Rationalization of Unalloyed Titanium Material Specifications to Current Production Capabilities Offers Opportunities for the Titanium Industry,” presented at Corrosion 2003, San Diego, California, March 16 to 20, 2003
3 Final Project Report, Phase 1, ASTM Strength Revision Project 151-02, October 15, 2003, Materials Technology Institute of the Chemical Process Industries, Inc., 1215 Fern Ridge Parkway, Suite 116, St. Louis, Missouri 63141-4405

 
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