Scope
B31.3 covers piping for petroleum refineries, chemical, pharma, textile, paper, semiconductor and cryogenic plants, and related processing facilities. It does not cover plumbing, fire protection, or piping inside ASME-stamped vessels.
Fluid service categories
- Category D — non-flammable, non-toxic, low P/T (limited use)
- Normal Fluid Service — the default for most process lines
- Category M — toxic; single exposure can cause serious harm
- High Pressure — owner-designated, uses Chapter IX
- Severe Cyclic Service — fatigue-driven design rules apply
Design conditions
- Design pressure: most severe coincident P/T expected in service
- Design temperature: metal temperature, not bulk fluid temperature
- Allowances: corrosion, erosion, mechanical, thread/groove depth
- Loads: weight, thermal, wind, seismic, occasional
What you should walk away with
Ability to read a line list, identify the fluid service category, locate the right allowable stress, and understand why the project specification often adds requirements above the code minimum.
Use of this content
This page is a decision-support and training reference. It is not a substitute for the governing code, the project specification, or the judgement of a responsible engineer. Always validate against the current edition of the applicable standard before use on live engineering work.