ASTM A312

Covers — austenitic stainless steel pipe:

• Common grades: TP304/304L, TP316/316L, TP321, TP347.
• Seamless (SMLS), Welded (WLD), and Heavily Cold Worked (HCW) manufacturing types.
• Intended for corrosive service and elevated temperatures.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Ferritic, martensitic, or duplex stainless steels → ASTM A790 (Duplex) or others.
• Pipe with filler metal added in welding → ASTM A358.
• Dimensional sizing → ASME B36.19M or B36.10M.

A312 establishes the material integrity of stainless pipe:

• Materials & Manufacture — welded pipe must be made by an automatic welding process with NO addition of filler metal.
• Chemical Composition — precise limits on Chromium and Nickel for corrosion resistance, and Carbon for weldability.
• Heat Treatment — requires solution annealing (heating to high temperature and rapid quenching) to dissolve chromium carbides and restore full corrosion resistance.
• Testing — requires hydrostatic or NDE testing, plus flattening/bending tests for weld ductility.

A312 pipes rely on their passive chromium-oxide layer for corrosion resistance.

Grade Variations ("L" and "H")

• Standard Grades (e.g., 304, 316): Standard carbon content.
• "L" Grades (e.g., 304L, 316L): Low carbon (max 0.035%). Essential for welding to prevent carbide precipitation (sensitization) which causes intergranular corrosion. Lower allowable stress than standard grades.
• "H" Grades (e.g., 304H): Higher carbon, required for high-temperature strength (creep resistance).

Dual certification (e.g., 316/316L) is common, meaning the steel has the low carbon of the "L" grade but meets the higher strength requirement of the standard grade.

Where to find it in the code: Chemical requirements → Table 1 · Heat treatment → Table 2.