ASTM B861 Grade 2 Seamless Titanium Pipe: UNS R50400 Data
Sep 09, 2025
What ASTM B861 Grade 2 Covers
ASTM B861 is the specification for seamless titanium and titanium alloy pipe for general corrosive service. Where ASTM B338 covers heat-transfer tube specified by outside diameter and wall, B861 covers pipe ordered by nominal pipe size and schedule, which makes it the usual choice for process lines, headers and manifolds. Grade 2 is the workhorse commercially pure grade of the specification, registered as UNS R50400 and known in the European designation system as W.Nr 3.7034.
The ASME equivalent is SB861, used where the pipe forms part of a code-constructed pressure system. Chinese practice refers to the same material as TA2 under GB/T 3620.1, and ISO 5832-2 lists the composition as Type 2 in the surgical-implant series.
Chemical Composition of Grade 2
| Element | Requirement |
|---|---|
| Titanium | Balance, nominally 99.2 % minimum excluding intentional additions |
| Iron | 0.30 % max |
| Oxygen | 0.25 % max |
| Nitrogen | 0.03 % max |
| Carbon | 0.08 % max |
| Hydrogen | 0.015 % max |
Grade 2 differs from Grade 1 mainly through a higher permitted oxygen content, which is what gives it the higher strength. Both remain single-phase alpha titanium with no intentional alloying additions.
Mechanical Properties and Comparisons
Seamless pipe to ASTM B861 in Grade 2 must show minimum annealed tensile strength of 345 MPa (50 ksi), 0.2 % offset yield strength of 275 MPa (40 ksi) and 20 % elongation. Typical mill results sit between roughly 440 MPa and 540 MPa tensile. Figures that present 539 MPa as the required minimum for Grade 2 pipe do not correspond to the standard: 539 MPa is a typical rather than a specified value, and purchase documents should cite the 345 MPa minimum. Likewise, expected elongation is 20 % minimum, not 25 %.
Density 4.51 g/cm3, melting point 1668 C, elastic modulus near 103 GPa and thermal conductivity around 15-16 W/(m*K) are the values normally entered into heat-transfer and flexibility calculations.
Size Range, Tolerances and Testing
Seamless Grade 2 pipe is produced from roughly NPS 1/8 up to NPS 24, with heavier walls available in the smaller sizes. Wall is ordered by schedule or by nominal wall in millimetres, and B861 sets the permitted variation on outside diameter, wall, length and straightness. Testing normally includes tensile testing, flattening, hydrostatic or an approved non-destructive pressure alternative, and eddy-current or ultrasonic examination when specified.
Ultrasonic testing is often requested for thicker walls and critical service, while eddy current is more common on thin-wall and heat-transfer items. Pipe is supplied annealed with a bright, pickled or blasted surface finish, and ends may be plain, bevelled or threaded to suit the connection method.
Corrosion Performance in Service
Grade 2 develops a stable passive film and performs well in seawater, chlorides, oxidising acids and many neutral process streams. Reported corrosion rates in flowing seawater generally stay below 0.01 mm per year, and the grade outperforms 316L stainless steel in chloride-bearing service. It is not the right choice for strongly reducing acids, nor for crevices in hot chlorides, where a palladium-bearing grade such as Grade 7 or a molybdenum-nickel grade such as Grade 12 should be evaluated instead.
Two practical limits deserve attention. Titanium is not suitable for dry chlorine service or for anhydrous oxygen, and it can be attacked by anhydrous methanol under certain conditions. Hydrogen uptake must also be controlled where cathodic protection is applied, because titanium can absorb hydrogen if the potential is driven too negative.
Fabrication, Welding and Applications
Grade 2 pipe is readily cold formed and is welded by gas tungsten arc, plasma or laser processes under complete inert shielding, with ERTi-2 filler for full-penetration joints. Bending and flanging are performed cold with allowance for springback, and thermally cut edges are mechanically cleaned to remove contaminated metal before welding. Typical applications include chemical-process piping, desalination and brine lines, flue-gas desulphurisation, pulp and paper process circuits, offshore seawater systems and power-plant cooling water pipework.
FAQ
Q: What is the difference between ASTM B861 and ASTM B338?
B861 covers seamless pipe ordered by nominal pipe size and schedule for general corrosive service, while B338 covers heat-transfer tube ordered by outside diameter and wall thickness.
Q: Is UNS R50400 the same material as W.Nr 3.7034?
Yes. Both designate commercially pure Grade 2 titanium in different numbering systems, and the Chinese designation for the same composition is TA2 under GB/T 3620.1.
Q: What is the minimum yield strength of Grade 2 seamless pipe?
275 MPa (40 ksi) at 0.2 % offset in the annealed condition, with 345 MPa (50 ksi) minimum tensile strength and 20 % minimum elongation.
Q: Can Grade 2 pipe be used in seawater?
Yes, and it is widely used for that purpose. Crevice conditions under deposits and gaskets are the main risk, so bolted and flanged joints need attention.
Q: When should Grade 7 or Grade 12 be used instead?
When the service involves reducing acids or hot chloride crevices. Grade 7 adds palladium and Grade 12 adds molybdenum and nickel specifically to resist those conditions.
Q: What is TA2 pipe?
TA2 is the Chinese grade designation for commercially pure titanium of Grade 2 level, and pipe supplied to GB/T 3624 or GB/T 3625 is dimensionally ordered by the Chinese pipe system rather than by ASTM schedule.
