ASME B31.3: Process Piping Code
Code for process piping in chemical, petroleum, and power generation industries. ASME B31.3 specifies inspection and NDT requirements for process piping systems.
The American Society of Mechanical Engineers (ASME) writes the boiler, pressure vessel, and piping codes that almost every U.S. jurisdiction has adopted by reference into law.
For pressure equipment built or operated in the United States, ASME compliance is rarely optional — state boiler-and-pressure-vessel inspectors enforce it directly.
ASME B31.3 is invoked when the scope of work matches its title — process piping code — and when the contract or regulatory regime cites it as the controlling document. In power and nuclear work, the inspection plan is built directly off the standard's tables; an auditor will cite the paragraph that was followed (or the one that was missed) when writing a finding. On petroleum and petrochemical equipment, ASME B31.3 usually feeds into a written mechanical-integrity program: inspection intervals, examination methods, and acceptance criteria are all traced back to a clause number in the document.
Methods covered
Industries
- Oil & Gas
- Petrochemical
- Power Generation
- Personnel qualification: examinations under ASME B31.3 must be performed by inspectors qualified and certified to a recognised scheme (typically ASNT SNT-TC-1A, CP-189, or ISO 9712 depending on jurisdiction), with documented training hours, vision tests, and a controlling written practice.
- Written procedure: every examination requires a written, controlled procedure that names the method, equipment, calibration steps, scanning pattern, and acceptance criteria — and is qualified before first use.
- Equipment verification: ultrasonic instruments must be verified against a calibration block (V1, V2, IIW, or job-specific reference) at intervals defined by the procedure — typically before use, every four hours of scanning, on operator change, and at end of shift.
- Image-quality verification: every radiograph or digital exposure carries a penetrameter / IQI of the type and thickness specified by the standard; the IQI must be visible and at the required sensitivity for the radiograph to be acceptable.
- Radiation safety: source handling, exclusion zones, dosimetry, and source recordkeeping must follow the licensing authority's rules in addition to the inspection standard itself.
- Acceptance criteria: indications are evaluated against the standard's tabulated limits (length, depth, alignment, frequency); any indication exceeding the criteria is recorded, dispositioned, and either repaired or evaluated for fitness-for-service.
- Documentation: examination reports must include enough information for a third party to reproduce the inspection — equipment serial numbers, calibration records, inspector ID, sketches of indications, and the controlling procedure revision.
- Code reference and edition: the ASME edition in force at the time of construction (or as amended by jurisdictional adoption) controls the rules; inspection records must cite the edition and addenda that were applied.
- Latest Edition
- 2024
- First Published
- 1955
- Scope
- Process Piping — design, materials, fabrication, examination, and testing of piping in chemical, petroleum, and related processing plants.
- Acceptance Criteria
- Table 341.3.2 — acceptance criteria for welds by service category (Normal, Cat-D, Cat-M, Severe Cyclic).
- Calibration / Qualification
- Welding per ASME IX; NDE per ASME V; examiner per Owner's Inspector or qualified per Owner's program.
Key Clauses Inspectors Cite
- Cl. 304 — Pressure design of piping components
- Cl. 331 — Welding
- Cl. 341 — Examination
- Cl. 344 — Types of Examination
- Cl. 345 — Testing
Companion / Parent Standards
ASME B31.1 · ASME B31.4 · ASME B31.8 · ASME Section V · ASME Section IX · API 570
Sample Contract Language
“All process piping shall be designed, fabricated, inspected and tested per ASME B31.3-2024, Normal Fluid Service; examination per Cl. 341 Table 341.3.2.”
ASME publishes a new edition of its codes on a fixed three-year cycle (with addenda and code cases issued between editions). Recent editions of ASME B31.3 have generally tightened personnel qualification language, expanded coverage of advanced ultrasonic methods (PAUT, TOFD) as accepted alternatives to radiography, and clarified the treatment of digital radiography and computed radiography. Inspection records should always cite the specific edition and addenda that were applied — codes are not retroactive, but new construction is always to the current edition unless a contract freezes an earlier one.
A typical refinery turnaround applies ASME B31.3 to the inspection scope for high-temperature piping and pressure vessels: corrosion-monitoring locations are read with UT thickness gauges, girth welds on repaired sections are radiographed or PAUT-scanned, and any indication outside the standard's acceptance table is dispositioned through API 579 fitness-for-service before the unit restarts.
What does ASME B31.3 cover?
ASME B31.3 (Process Piping Code) is published by ASME. Code for process piping in chemical, petroleum, and power generation industries.
Is ASME B31.3 mandatory or voluntary?
ASME B31.3 is a consensus standard. It becomes mandatory when invoked by a contract, by another code that cites it (for example ASME Section V calling out an ASTM practice), or by a regulator that has adopted it into law in a specific jurisdiction.
Who is qualified to perform inspections under ASME B31.3?
Inspections under ASME B31.3 must be performed by personnel qualified and certified to a recognised NDT certification scheme — most commonly ASNT SNT-TC-1A or CP-189 in the United States, ISO 9712 in much of the rest of the world, and NAS 410 for aerospace work. The written practice that controls qualification must be in place before any examination is started.
Which edition of ASME B31.3 should I use?
New construction follows the edition of ASME B31.3 in force at the time the contract is signed (or the edition adopted by the controlling jurisdiction). In-service inspection generally follows the edition that was in force when the equipment was built, unless the operator's mechanical-integrity program adopts a later edition by reference.
Standard Code
ASME B31.3
Organization
ASME
Methods Covered
3 method(s)
Industries
3 sector(s)
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