ASTM A312 Stainless Steel Pipe

Choosing Between 304 and 316

TP304 is the general purpose austenitic stainless steel, containing 18 percent chromium and 8 percent nickel. It offers excellent resistance to a wide range of organic and inorganic chemicals and to atmospheric corrosion. TP316 adds 2 to 3 percent molybdenum, which substantially improves resistance to chlorides and to pitting and crevice corrosion. The practical rule is: use 304 for benign chemical environments and general industrial duty; use 316 wherever chlorides are present, including seawater, brine, coastal atmospheres and many process streams. The L grades (304L and 316L) have a maximum carbon content of 0.030 percent, which prevents sensitization, that is the precipitation of chromium carbides at grain boundaries during welding, and are therefore preferred for welded construction.

Seamless or Welded Stainless Pipe?

ASTM A312 permits both seamless and welded pipe, and welded pipe may be supplied either as-welded or cold worked to meet the same mechanical requirements. For most corrosive service the welded product performs equivalently to seamless, provided the weld is properly made and the pipe is solution annealed and pickled. Welded pipe is considerably more economical in larger sizes and thinner walls. However, some end users and specifications still restrict stainless pipe in critical service to seamless construction, and for high pressure or cyclic service seamless remains the conservative choice. If your specification permits welded, confirm whether the weld seam must be radiographed and whether the pipe will be supplied in the annealed condition.