ASME B31.3 vs. B31.1: choosing the right piping code for your project
Every pipe spool that leaves our Brookshire shop is built to a code, and the two we work with most are ASME B31.3 (Process Piping) and ASME B31.1 (Power Piping). Choosing the wrong one is not a paperwork problem: it changes wall thickness, weld acceptance criteria, NDE percentages and the documentation your inspector will ask for.
Where each code applies
B31.3 covers piping in petroleum refineries, chemical and petrochemical plants, pharmaceutical and terminal facilities. It is the default for most of the Gulf Coast work we fabricate. B31.1 covers power generation, including boiler external piping, steam and feedwater systems in utility and industrial power plants.
What changes in the shop
- Design allowables: B31.1 is generally more conservative on allowable stress, which can mean heavier schedules.
- NDE: B31.3 categorizes fluid service (Normal, Category D, M, high-pressure) and sets radiography percentages accordingly; B31.1 ties examination to pressure and temperature thresholds.
- Weld acceptance: the criteria tables differ, so a weld that passes under one may be rejectable under the other.
- Traceability: both require material certification, but the owner’s spec usually adds requirements we bake into our weld maps and MTR packages.
How Silverfox approaches it
We confirm the governing code and the owner’s piping specification at kickoff, qualify the WPS/PQR set for the material and process (FCAW, SAW, GTAW or GMAW), and issue a documentation package that matches the code the authorized inspector will audit. If your project spans both, for example a cogeneration unit inside a chemical plant, we set the boundary on the isometrics before fabrication starts.
Need help selecting the code or reviewing a spec? Talk to our engineering team.
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