ASTM B861 Grade 7 Titanium Alloy Seamless Wastewater Pipes

What ASTM B861 Grade 7 Pipe Is

ASTM B861 covers seamless and welded titanium and titanium alloy pipe for general corrosion-resisting and elevated-temperature service. Grade 7 (UNS R52400, W.Nr. 3.7235) is commercially pure titanium modified with 0.12-0.25% palladium, and is designated Ti-0.15Pd. The palladium addition shifts the alloy into the cathodic range, promoting rapid repassivation of the oxide film in reducing acids and crevice conditions where unalloyed titanium breaks down. The result is a pipe with the same formability and weldability as Grade 2 but markedly better resistance to pitting, crevice corrosion, and stress corrosion cracking in hot chlorides and weak reducing acids.

Chemical Composition (ASTM B861)

Mechanical Properties

Grade 7 pipe is supplied in the annealed condition with minimum tensile strength of 345 MPa (50 ksi), minimum yield strength of 275 MPa (40 ksi) at 0.2% offset, and minimum elongation of 20% in 50 mm. Density is 4.51 g/cm3, about 60% of carbon steel. These values match Grade 2, so piping systems can be designed with identical wall thickness rules while gaining the corrosion margin of the palladium addition.

Why Grade 7 for Wastewater and Chemical Lines

Wastewater systems carry chlorides, sulfides, wet chlorine, and low-pH streams that pit stainless steel and crevice-corrode standard titanium. Grade 7 pipe is specified for chlorination systems, flue gas scrubbers, outlet ducting, stack liners, acid production and pickling lines, pulp and paper bleach plants, and nuclear fuel reprocessing service. In hot brine and seawater heat exchangers, the palladium addition suppresses crevice attack at tube-to-tubesheet joints, which is the dominant failure mode of Grade 2 in that duty.

Procurement and Fabrication Notes

Specify seamless pipe to ASTM B861, or welded pipe to ASTM B862, with dimensions in NPS or metric OD, and schedule per the design code.

Require EN 10204 type 3.1 mill certificates covering chemistry, tensile results, flattening, and hydrostatic testing; type 3.2 with third-party witness where the project demands it.

Weld with argon shielding on both sides and matching ERTi-7 filler; keep interpass temperature low and confirm weld color is silver or light straw as a contamination check.

Confirm availability in the required size range: seamless pipe from 1/4" NB upward, wall thicknesses from Schedule 10 to Schedule 160, and lengths as random or cut lengths.

FAQ

What is the difference between Grade 7 and Grade 2 titanium pipe?

Grade 7 adds 0.12-0.25% palladium to Grade 2 chemistry. Mechanical properties are nearly identical, but Grade 7 resists crevice corrosion and reducing acids much better, which is why it is preferred for wastewater, hot brine, and chemical processing lines.

Is Grade 7 titanium pipe weldable?

Yes. Grade 7 has the same weldability as Grade 2. Use ERTi-7 filler and argon shielding on the root and back side; post-weld cleaning and color inspection are the same as for other titanium grades.

What standards cover Grade 7 pipe?

ASTM B861 (seamless pipe), ASTM B862 (welded pipe), and ASTM B338 (tube for condensers and heat exchangers), with ASME equivalents SB861, SB862, and SB338 for pressure applications.

Why is palladium added to titanium?

Palladium acts as a cathodic modifier that keeps the titanium surface in the passive range, so the oxide film re-forms quickly if damaged. This suppresses pitting and crevice attack in hot chlorides and weak reducing acids.

When should I choose Grade 12 instead of Grade 7?

Grade 12 (Ti-0.3Mo-0.8Ni, UNS R53400) is roughly 40% stronger than Grade 7 and resists crevice corrosion in hot brines at moderate temperatures. Choose Grade 12 when pressure rating or wall thickness drives the design; choose Grade 7 for maximum corrosion margin in chloride and reducing-acid service.