ASTM B337 Grade 7 Welded Titanium Pipe for Oil and Gas Exploration
Oct 17, 2025 ASTM-B337.pdf
Grade 7 welded titanium pipe is the form most often requested for oil and gas projects that handle chloride-rich produced water, and ASTM B337 is the specification that governs it. The palladium addition is what makes the grade interesting in that service, because produced water combines chlorides, elevated temperature and occluded crevices under supports and at flanges.
Why Grade 7 for Oil and Gas Duty
Unalloyed Grade 2 titanium performs well in seawater and in many process streams, but its weak point is the crevice. Where a gasket, a pipe support or a thread root keeps a small volume of chloride solution stagnant at elevated temperature, the local environment becomes acidified and oxygen-starved, and the passive film can break down. Adding 0.12 to 0.25 % palladium, as in Grade 7, shortens the time needed to repassivate after such a breakdown, so the grade tolerates the geometry that Grade 2 does not.
Oil and gas service also brings carbon dioxide, traces of hydrogen sulphide and sand. Titanium handles carbon dioxide and chlorides well. Where hydrogen sulphide is present in meaningful partial pressure, the duty should be assessed project by project, because titanium is not covered as a routine sour service material by the usual international sour service guidance.
The Specification Set
| Specification | Scope |
|---|---|
| ASTM B337 | Welded titanium pipe, the base specification for this product |
| ASTM B338 | Seamless and welded titanium tube, the parent specification for welded tube |
| ASTM B862 | Welded titanium pipe stated in metric sizes |
| ASME SB-337 / SB-338 / SB-862 | ASME editions used for code-registered piping |
| AMS 4942 | Aerospace material specification for welded titanium tubing |
Chemical Composition of Grade 7
| Element | Limit |
|---|---|
| Titanium | Balance |
| Carbon | 0.08 % max |
| Iron | 0.30 % max |
| Hydrogen | 0.015 % max |
| Nitrogen | 0.03 % max |
| Oxygen | 0.25 % max |
| Palladium | 0.12 to 0.25 % |
Equivalents are UNS R52400 and Werkstoff 3.7235.
Mechanical Properties and Size Range
| Property | Grade 7 value |
|---|---|
| Density | 0.163 lb/in3, about 4.51 g/cm3 |
| Tensile strength, min | 50 ksi (345 MPa) |
| Yield strength, 0.2 % offset, min | 40 ksi (275 MPa) |
| Elongation, min | 20 % |
Welded pipe is normally supplied from one half inch nominal bore to 24 inch nominal bore. Light and standard wall thicknesses follow ASME B36.19M for schedules 5S, 10S, 40S and 80S, while heavier walls including Schedule 160 and XXS follow ASME B36.10M, which defines the complete range of schedules, standard, extra strong and double extra strong wall thicknesses. Wall thickness up to about 12 mm is common in welded Grade 7 production. Ends are supplied plain, bevelled or threaded, and lengths are single random, double random or cut to an exact requirement up to about 12 m.
Manufacture of Welded Grade 7 Pipe
Welded pipe starts as strip or plate, is formed into a cylinder, and is joined by an autogenous weld made under full inert-gas shielding. For titanium this shielding is not optional: the weld pool and the hot metal behind it must be protected from air until the temperature falls below roughly 400 °C, which is normally achieved with trailing gas shields and, for tube, internal purging. Completed pipe is then welded end to end if longer lengths are required, radiographed on the longitudinal seam, hydrotested and finally annealed and pickled. A weld that has picked up colour, from straw through blue to grey, indicates contamination and is rejected on sight.
Where the Grade Fits in a Facility
Typical uses include produced water and injection lines, seawater cooling circuits, chlorine and hypochlorite dosing lines, and exchanger shells and tails where the fluid is aggressive. Because welded pipe is made in continuous lengths with a single longitudinal seam, it is the economical option for larger diameters; seamless pipe to ASTM B861 remains the choice for the smallest bores and for the highest pressure ratings.
Frequently Asked Questions
Q: What is the difference between ASTM B337 and ASTM B338?
A: ASTM B338 covers titanium tube in both seamless and welded forms, while ASTM B337 is dedicated to welded titanium pipe, which is a larger diameter, thicker wall product delivered to pipe dimensions.
Q: Is Grade 7 suitable for sour service?
A: Not as a general rule. Titanium is not automatically covered by routine sour service guidance, so any duty with meaningful hydrogen sulphide partial pressure needs a project-specific assessment covering grade, temperature and stress.
Q: Which schedules are available in welded Grade 7 pipe?
A: Schedules 5S to 80S follow ASME B36.19M, while Schedule 160, XXS and the intermediate schedules follow ASME B36.10M. Wall thickness up to about 12 mm is common in welded production.
Q: What does the palladium addition cost in mechanical terms?
A: Nothing in practice. Minimum tensile strength of 345 MPa, yield strength of 275 MPa and 20 % elongation apply, matching Grade 2.
Q: How is weld quality verified on welded Grade 7 pipe?
A: Weld colour is checked against the acceptance photographs in the specification, the longitudinal seam is radiographed, and the finished pipe is hydrotested. A contaminated weld shows visible oxide colour and is rejected.
