ASME B31.3 Process Piping is the dominant process-piping code globally for refining, petrochemical, chemical, fine chemical, pharmaceutical, semiconductor, pulp & paper, and cryogenic facilities. It governs the design, materials, fabrication, examination, testing, and inspection of metallic + nonmetallic piping carrying hydrocarbons, hazardous fluids, utility fluids, and process chemicals. B31.3 is referenced by OSHA PSM (29 CFR 1910.119), EPA RMP, API 570 Piping Inspector in-service inspection, and dozens of jurisdictional + EPC contract specs.
\n\nB31.3 assigns piping to fluid services, each with different design and examination requirements. The owner is responsible for designating Category D, Category M, High Pressure and Elevated Temperature fluid services and for specifying Severe Cyclic conditions where they apply:
\nPressure design thickness for straight pipe is t = PD / (2(SEW + PY)), with allowable stress S from Appendix A, the longitudinal weld joint quality factor E (Table A-1B), the weld joint strength reduction factor W and the coefficient Y from Table 304.1.1. Typical E values: seamless pipe 1.00, electric resistance welded (ERW) 0.85, furnace butt-welded 0.60, and electric fusion welded pipe 0.80 to 1.00 depending on joint type and radiography. Add mechanical, corrosion and erosion allowances and mill tolerance to get the minimum thickness to order.
\nB31.3 welding follows ASME Section IX for WPS, PQR and welder qualification, with additional B31.3 requirements in § 328. P-Numbers (base metal grouping), F-Numbers (filler-metal grouping) and A-Numbers drive the qualification matrix. Preheat and postweld heat treatment follow § 330 and § 331 (Table 331.1.1), which set requirements by P-Number and thickness; check the edition in force because these tables have changed in recent editions.
\nCommon consumable choices: E7018 SMAW for carbon steel, ER70S-6 GMAW, and ER309L for stainless-to-carbon dissimilar welds. Atlantis ERP can hold WPS, PQR and welder-qualification records so continuity checks are easier across multi-site projects.
\nRequired examination extent by fluid service (summary; confirm against the edition in force):
\nExamination methods follow ASME Section V (Article 2 RT, Article 4 UT, Article 6 PT, Article 7 MT, Article 9 VT). Acceptance criteria are in B31.3 Table 341.3.2 by weld type and fluid service.
\nB31.3 requires a leak test before service. The default hydrostatic test is at not less than 1.5 times design pressure, adjusted for the ratio of allowable stress at test and design temperatures (§ 345.4.2); a pneumatic test is at 1.1 times design pressure with additional safeguards (§ 345.5). The test pressure is held for at least 10 minutes and then all joints are examined. Category D piping may use an initial service leak test; alternatives exist under § 345.9.
\nB31.3 is the construction code. Once piping enters service, API 570 governs in-service inspection: CMLs per circuit, corrosion-rate and remaining-life calculations, intervals by piping class, and repairs and alterations. Damage beyond API 570's acceptance rules may go to an engineering API 579-1 assessment, and some owners set intervals with an RBI assessment per API RP 580. Atlantis NDT does not provide RBI or FFS services; its ASNT Level III consulting covers NDE procedures and written practices.
\n| Dimension | B31.3 Process | B31.1 Power |
|---|---|---|
| Industry | Refining, chemical, petrochemical, pharmaceutical | Power generation, steam plants, district heating |
| Typical fluids | Hydrocarbons, chemicals, utilities | Steam, water, fuel gas and oil |
| Jurisdiction | Generally adopted by owner or contract | Boiler external piping falls under ASME Section I jurisdictional rules |
| Examination extent | By fluid service (Normal, D, M, Severe Cyclic, High Pressure) | By service conditions and weld type (B31.1 Table 136.4) |
| Cyclic loading | Severe Cyclic Conditions and stress-range factors | Stress-range reduction factors for cyclic conditions |
A: Owner / process licensor assigns the fluid-service category. Look for the project P&ID legend — Category M services are explicitly flagged. Fluids commonly evaluated for Category M designation include highly toxic materials such as phosgene; the designation is the owner's decision based on the fluid and exposure risk. When in doubt, ask the process safety engineer.
\nA: Category D is benign service — non-flammable, non-toxic, low pressure (≤ 150 psig), moderate temperature. Normal is the default for everything else not Category D / M / Severe Cyclic / K. Most refinery + chemical process piping is Normal.
\nA: Yes — B31.3 is a private-consensus standard. EPC contracts globally specify it even where no government regulation requires it. The owner / EPC contract decides the governing code. Some countries (e.g., Saudi Aramco SAES-L-150, ADNOC ACS-01) overlay national specs on top of B31.3.
\nA: Yes for topsides process piping (refining + chem onshore design + EPC carries through to offshore production platforms). Subsea pipelines use ASME B31.4 (liquid) or B31.8 (gas) + DNV-OS-F101 / API RP 1111. Marine & offshore NDT services span both.
\nA: Per § 328.2.3 + ASME Section IX — qualified WPS for the actual base-metal combination is required. Carbon-to-stainless dissimilar welds typically use ER309L filler. CrMo-to-stainless requires careful filler selection (ENiCrFe-3 / Inconel 182 / 82) to manage carbon migration at the fusion line.
\nA: B31.3 = piping. ASME Section VIII = pressure vessels (drums, towers, heat exchangers, separators). Both reference ASME Section IX for welding qualification and ASME Section V for NDT methods. The owner / EPC team manages the interface (typically the vessel nozzle is ASME VIII; the connected piping flange is B31.3).
\nA: Large projects need per-joint traceability: WPS and welder for each weld, NDE reports, PWHT charts, hardness results where specified, and test records. Teams typically manage this in a document-control or inspection-management system; Atlantis ERP can hold these records alongside technician certifications.
\nA: A digital twin can link piping isometrics to thickness readings and inspection history so integrity teams can see CML data and corrosion trends in 3D. In the Atlantis Digital Twin platform, inspection data is displayed on the model; interval and remaining-life decisions stay with the authorized inspector and the owner's engineers.
\nAtlantis NDT is led by Anoop Rayavarapu (ASNT NDT Level III in UT, RT, MT, PT and VT). Free consultation for NDT inspection companies, training providers, and asset owners worldwide. request a demo — pricing varies by region and scope, quote on request.
","order":0,"createdAt":"2026-06-17","updatedAt":"2026-10-18","quickAnswer":{"question":"What does ASME B31.3 cover?","answer":"ASME B31.3 Process Piping (current edition 2024) governs the design, fabrication, examination and testing of process piping in petroleum refineries, chemical, pharmaceutical, textile, paper, semiconductor and cryogenic plants. It assigns fluid services — Normal, Category D, Category M, High Pressure (owner-designated) and Severe Cyclic Conditions — each with different examination extent and acceptance.","bullets":["Normal Fluid Service: visual of at least 5% of fabrication plus at least 5% random RT/UT of circumferential butt and miter welds","Category D: visual examination only; Category M: 100% visual plus a larger random RT/UT sample","Severe Cyclic: 100% RT/UT of circumferential butt and miter welds plus MT/PT of socket and branch welds not radiographed"]}}