PIPE FITTINGS · TECHNICAL ANSWER

What is the difference between ASME B16.9 and ASTM A403?

ASME B16.9 primarily defines dimensions, tolerances, ratings, testing and marking for factory-made wrought butt-weld fittings. ASTM A403 defines austenitic stainless-steel fitting materials and product classes.

DETAILED EXPLANATION

A complete stainless fitting description commonly needs both—for example ASTM A403 WP316L, ASME B16.9, 4-inch, SCH 40S, seamless elbow.

The dimensional and material standards perform different jobs.

Key points

  • B16.9: dimensional/product form standard
  • A403: stainless material specification
  • Grade and fitting class must be stated
  • Size and schedule complete the description
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