ASTM B338 Grade 12 Cold Drawn Titanium Tube: UNS R53400 Data

Grade 12 Titanium Tube: What the Grade Designation Means

Grade 12, registered as UNS R53400 and covered by ASTM B338 for tube, is a near-alpha titanium alloy produced by adding molybdenum and nickel to a commercially pure titanium base. The standard addition is 0.2-0.4 % molybdenum and 0.6-0.9 % nickel. Together they raise the corrosion potential of the alloy and make it considerably more resistant to crevice attack and to mildly reducing acids at elevated temperature than unalloyed Grade 2.

The grade is often confused with Grades 7, 11 and 16, which achieve a similar improvement with palladium instead of molybdenum and nickel. The two families are not interchangeable on paper. The molybdenum-nickel grade performs well in hot chlorides and is far less exposed to palladium price and availability, while the palladium family is generally preferred where strongly reducing acids are involved.

Chemistry, Standards and Equivalents

The grade appears in ASTM B265 for sheet, strip and plate, B337 for seamless pipe, B338 for tube, B348 for bar and billet, and B381 for forgings, where the forging designation is F-12. Its unified numbering system entry is R53400. Buyers should verify which of these product specifications applies, because mechanical requirements and tolerances differ between them.

Mechanical and Physical Properties

The annealed minimum properties expected of Grade 12 tube are 483 MPa (70 ksi) tensile strength, 345 MPa (50 ksi) yield strength at 0.2 % offset, and 18 % elongation. That is a distinct step above the 345 MPa, 275 MPa and 20 % combination that applies to Grade 2. Density is 4.51 g/cm3, elastic modulus approximately 103-107 GPa and thermal conductivity about 15-17 W/(m*K), with a quoted beta transus near 890 C (1634 F).

Because the grade is a near-alpha alloy, it is not strengthened by solution treatment and ageing. It is supplied annealed, and any thermal treatment serves to restore ductility and relieve residual stress from cold drawing rather than to raise strength.

Cold Drawing: How B338 Grade 12 Tube Is Made

Cold drawing starts from a hollow that has been hot extruded or hot rolled and then conditioned by machining or grinding. The shell is pointed, lubricated and pulled through a die over a mandrel that controls the wall, reducing diameter and wall in a controlled pass. Several passes are needed, with an intermediate recrystallisation anneal between them to restore ductility; between anneals the tube is descaled and pickled in nitric-hydrofluoric acid, then rinsed and dried.

Finishing operations include a final pass for dimensional control, vacuum or inert-gas annealing in roughly the 700-790 C range for this chemistry, straightening, cutting to length, and full-length eddy-current examination. Tubes are also pressure tested where requested, and U-bends are formed and stress relieved.

Corrosion Behaviour and Applications

Grade 12 is selected where hot chloride-bearing streams attack the crevices of a heat exchanger and where dilute reducing acids are present at moderate temperature. Typical applications are refinery and petrochemical heat exchangers, brine and salt-evaporation equipment, chemical-process vessels and piping, and marine systems. In seawater the general corrosion rate of titanium is negligible, so the practical failure mode in these environments is crevice attack under deposits rather than uniform wall loss, which is exactly the mode Grade 12 is designed to resist.

Terminology: Tube, Pipe and the Cold Drawn Pipe Label

Descriptions of this product often call it a cold drawn pipe, which mixes two different ASTM systems. ASTM B338 covers tube, generally specified by outside diameter and wall thickness for heat-transfer service, while ASTM B861 covers seamless pipe for general corrosive service and ASTM B862 covers welded pipe, both ordered by nominal pipe size and schedule. A cold-drawn seamless heat-transfer product remains a B338 tube even when it is offered in pipe-like outside diameters, and the mill certificate should state which dimensional system the tolerances follow, because pipe and tube tolerances are not the same.

Fabrication and Welding Notes

Grade 12 responds well to gas tungsten arc welding with ERTi-12 filler under the same fully inert conditions required for other titanium grades. Forming is done cold with attention to springback. Machining calls for sharp tooling, generous coolant flow and moderate cutting speeds because of the low thermal conductivity of titanium. Iron contamination introduced by steel tooling or steel brushes is a frequent cause of localised corrosion and should be excluded from the shop-floor area used for titanium work.

FAQ

Q: Is Grade 12 the same as Grade 2?
No. Grade 12 contains 0.2-0.4 % molybdenum and 0.6-0.9 % nickel, has higher minimum strength, and tolerates hot chlorides and crevices far better than unalloyed Grade 2.

Q: Why is Grade 12 called a near-alpha alloy?
Its small additions stabilise the alpha phase with limited beta retention, so it behaves like an alpha alloy during fabrication while offering better corrosion resistance.

Q: What is the minimum yield strength of Grade 12 tube?
345 MPa (50 ksi) at 0.2 % offset in the annealed condition, with 483 MPa (70 ksi) minimum tensile strength and 18 % minimum elongation.

Q: Does Grade 12 need post-weld heat treatment?
Not normally. Welds in the annealed grade are left as welded when shielding was adequate; stress relief may be specified for U-bends or heavily cold-formed parts.

Q: Can Grade 12 be used in seawater heat exchangers?
Yes. It is widely used in chloride-bearing cooling and brine circuits, where resistance to crevice corrosion under deposits is the main advantage over Grade 2.

Q: Why is eddy-current testing specified on cold drawn tube?
Drawing can produce laps, seams and wall variation, and full-length eddy-current examination screens the whole length instead of only the ends used for destructive testing.