The ASTM B862 Specification
ASTM B862 establishes the requirements for welded titanium and titanium alloy pipe, covering grades 1 through 38 and the common alloy grades. The pipe is formed from strip or plate and closed with a longitudinal weld, then processed so that the weld zone meets the same strength and corrosion requirements as the parent metal. Grade 2, also written as Ti2, is the standard choice for the majority of chemical and marine piping duties.
Composition and Mechanical Properties
Grade 2 is commercially pure titanium with maximum limits of 0.30 percent iron, 0.25 percent oxygen, 0.08 percent carbon, 0.03 percent nitrogen and 0.015 percent hydrogen. Welded pipe in the annealed or stress relieved condition provides a minimum tensile strength of 345 MPa and a minimum yield strength of 275 MPa. Because the weld is produced in a controlled atmosphere, its strength is equivalent to the parent material and the pipe can be treated as a homogeneous pressure boundary.
Weld Quality and Integrity
The longitudinal weld is made by gas tungsten arc or plasma arc welding under inert gas protection, and the weld is examined by non-destructive methods such as ultrasonic, eddy current or radiographic testing. Flattening and reverse bend tests confirm that the weld has full penetration and ductility. For demanding services the pipe can be cold worked after welding to improve weld properties, and all pipe is pressure tested before delivery.
Corrosion Resistance for Chemical Service
Grade 2 welded pipe resists seawater, chlorides, oxidizing acids, alkalis and a wide range of process chemicals through its stable titanium dioxide film. The weld zone retains this resistance because the weld chemistry matches the parent metal and the surface oxide is removed after welding. This makes welded titanium pipe a reliable and economical alternative to seamless pipe in services where the pressure boundary is not extreme.
Applications in Chemical Processing
Welded Grade 2 pipe is used for process lines, transfer piping, heat exchanger piping, ventilation ducting and tank connections in chemical, pharmaceutical, pulp and paper, and desalination plants. It is also common in marine exhaust and ballast systems where long corrosion life is required. The availability of large diameters from welded construction makes it practical for main process headers that would be difficult to produce as seamless pipe.
Selection and Installation Guidance
Designers choose welded pipe when the operating pressure and temperature are within the accepted range for longitudinally welded construction and when large diameters are needed. Field joints are made with the same care as the mill weld, using clean surfaces, inert gas backing and qualified welders. The completed piping system is flushed and dried before service to remove debris that could damage the passive film.
Frequently Asked Questions
Q: What is the difference between ASTM B862 and ASTM B861 pipe?
A: ASTM B862 covers welded titanium pipe with a longitudinal seam, while ASTM B861 covers seamless titanium pipe with no weld seam.
Q: Is welded titanium pipe as strong as seamless pipe?
A: When the weld is produced under controlled conditions and examined non-destructively, welded Grade 2 pipe meets the same tensile strength requirements as seamless pipe.
Q: Can welded Grade 2 pipe be used for corrosive chemicals?
A: Yes. The weld chemistry matches the parent metal and retains the corrosion resistance of Grade 2 titanium in chloride and oxidizing services.
Q: What testing is applied to the longitudinal weld?
A: The weld is examined by ultrasonic, eddy current or radiographic methods, and flattening and reverse bend tests verify weld ductility and penetration.
Q: What sizes are available in welded titanium pipe?
A: Welded pipe is available in a broad range of diameters and wall thicknesses, including large diameters that are impractical to produce as seamless pipe.
