Scope of ASTM B338
ASTM B338 covers seamless and welded titanium and titanium alloy tube for condensers and heat exchangers, including grades from commercially pure Grade 1 to high-strength alloys. The specification sets chemistry limits, tensile requirements and the manufacturing and testing rules for the tube.
Tube supplied to B338 is produced in straight lengths with controlled dimensions, and the specification is the standard purchasing document for heat exchanger tubing worldwide.
Grade 7 Properties
Grade 7, Ti-0.15Pd with UNS designation R52400, is a palladium-bearing grade with the strength of Grade 2. The minimum tensile strength is 345 MPa and the minimum yield strength is 275 MPa in the annealed condition.
The palladium content keeps the tube passive in reducing acids, hot brines and creviced conditions, where plain pure titanium suffers localised attack.
Tube Manufacturing Routes
Grade 7 heat exchanger tube is produced by the seamless route from pierced billet, or by the welded route from strip with the seam consolidated by welding, cold working and annealing. Both routes deliver tube that meets the same chemistry and performance requirements.
Welded tube is generally selected for large diameters and long lengths, while seamless tube is preferred where a uniform structure across the wall is required.
Testing Requirements
Under ASTM B338, each tube is checked for dimensions, and samples are tested for tensile properties, flattening and flaring behaviour. Welded tube is examined by eddy current or ultrasonic testing of the weld zone, and every tube is pressure tested.
Supplementary tests such as hydrostatic testing at higher pressure, ultrasonic full-length examination and corrosion testing can be ordered as options for critical service.
Applications in Heat Exchange Service
Grade 7 tube is used in shell-and-tube heat exchangers, condensers and reboilers handling hot chlorides, dilute mineral acids, seawater and process brines. It is the standard choice where the medium would pit or crevice-corrode plain titanium tube.
The long service life of Grade 7 tube, measured in decades in aggressive duty, justifies its use in chemical plants, desalination units and offshore facilities.
Frequently Asked Questions
Q: What is ASTM B338?
A: ASTM B338 is the specification for seamless and welded titanium tube for condensers and heat exchangers.
Q: What is the strength of Grade 7 tube?
A: Grade 7 has a minimum tensile strength of 345 MPa and a minimum yield strength of 275 MPa in the annealed condition.
Q: Why is Grade 7 chosen for corrosive service?
A: The palladium addition resists reducing acids and crevice corrosion where plain pure titanium fails.
Q: How is welded B338 tube examined?
A: The weld zone is examined by eddy current or ultrasonic testing, and the tube must pass flattening and flaring tests.
Q: Can Grade 7 tube be supplied seamless?
A: Yes, Grade 7 heat exchanger tube is available by both seamless and welded routes under ASTM B338.
