ASTM A403

Covers — wrought austenitic stainless steel butt-welding fittings (elbows, tees, reducers) in grades WP304/304L, WP316/316L, WP321, WP347, with class designations recording the manufacturing/heat-treat route.

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

• Carbon/alloy-steel butt-weld fittings → ASTM A234.
• Austenitic stainless pipe → ASTM A312; stainless plate → ASTM A240.
• Fitting dimensions and ratings → ASME B16.9.

The grade class (W/WP/WX/WPW) tells you the forming and solution-anneal history — verify it for corrosive service.

A403 sets minimum requirements for stainless fittings:

• Chemistry — austenitic grade composition (304/316/321/347 and L variants).
• Mechanical Properties — tensile/yield/elongation for the grade.
• Heat Treatment — solution annealing (per class) to restore corrosion resistance after forming/welding.
• Testing — tension testing, intergranular-corrosion testing where specified, and PMI/heat certification.

ASTM A403 covers wrought austenitic stainless butt-welding fittings — the stainless analog of A234, matched to A312 stainless pipe. Grades WP304/WP316 and their low-carbon "L" variants serve corrosive and high-temperature process service.

The class designation (W, WP, WX, WPW) is important: it records whether the fitting was solution-annealed after forming/welding, which governs corrosion resistance. "L" grades resist weld sensitization for as-welded lines.

Engineering Note: For chloride or sensitization-prone service, specify the solution-annealed class and, where welding without post-weld anneal, the "L" grade — an unannealed WP316 fitting can sensitize at the weld.