ASME B31.8 Gas Pipeline 2026 — Inspection Requirements Decoded

ASME B31.8 for inspectors: the short answer

ASME B31.8, Gas Transmission and Distribution Piping Systems, covers gas pipelines, gas compressor stations, metering and regulation stations, gas mains, and service lines up to the outlet of the customer's meter set assembly. The latest edition is 2025. For US operators the binding inspection rules come from 49 CFR Part 192. Part 192 sets weld NDT percentages, adopts API 1104 for weld acceptance and requires integrity management under Subpart O, using ASME B31.8S for the programme. B31.8 provides the engineering framework those rules build on.

This section adds to the overview above and to our ASME B31.8 standard summary. It corrects several statements that apply generic plant-piping practice to gas pipelines, and it sets out where the inspection requirements for a US gas pipeline actually come from.

Corrections to the overview above

• Weld acceptance is not "ASME V Article 9 plus AWS D1.1". AWS D1.1 is the structural steel welding code and does not govern pipeline girth welds. For federally regulated gas pipelines, 49 CFR 192.241(c) sets weld acceptability by the standards in Section 9 or Appendix A of API Std 1104. Appendix A may not be used to accept cracks.
• Welder and procedure qualification is not "per ASME Section IX" alone. Part 192 allows welders to qualify under API 1104 or ASME Section IX. There is also a separate low-stress route in Appendix C of Part 192 for pipelines operating below 20% of SMYS. On cross-country line pipe, API 1104 is the usual basis.
• "In-service inspection follows PIM per 49 CFR 192/195". Part 195 covers hazardous liquid pipelines, not gas. Gas transmission integrity management is Part 192 Subpart O, which relies on ASME B31.8S. B31.8 itself also contains an operating and maintenance chapter (Chapter V), so it does more than set "construction and initial inspection requirements".
• "Inspector qualifications: ASNT Level II plus API 510/570/653". API 510, 570 and 653 are in-service codes for refinery and chemical-plant pressure vessels, piping and tanks. They do not apply to gas transmission pipelines. Part 192 requires NDT to be done to written procedures by people trained and qualified in those procedures and in the equipment used. Operator Qualification rules (Part 192 Subpart N) apply where the operator has designated the task as a covered task.
• "B31.8-qualified inspectors" and "3-6 month qualification". There is no B31.8 inspector qualification, and the timeline quoted in the earlier FAQ has no basis.
• Disposition "per BS 7910 / API 579 / NB-23". For gas pipelines, girth weld engineering critical assessment follows API 1104 Appendix A within its limits. Corroded pipe remaining strength is commonly evaluated with ASME B31G-type methods, which Part 192 references. Repairs follow the operator's procedures under Part 192. The National Board Inspection Code (NB-23) covers boilers and pressure vessels, not pipelines.
• PWHT charts and hardness maps are not routine items on carbon steel line pipe girth welds. They come into play only where the operator's specification, the material or the service calls for them, for example some sour-service applications.

Code versus regulation: B31.8, B31.8S, API 1104 and 49 CFR 192

B31.8 is a consensus code. 49 CFR Part 192 is federal law administered by PHMSA, and by state pipeline safety programmes for intrastate lines. Part 192 does not adopt the whole of B31.8. It incorporates specific documents and editions by reference for specific sections, listed in 192.7. The current eCFR lists:

• ASME B31.8 (2018 edition) for a small number of sections, including design-related and maximum allowable operating pressure provisions and part of the integrity management programme section.
• ASME B31.8S (2018 edition) across the Subpart O integrity management sections: threat identification, baseline and continual assessment, reassessment intervals, preventive and mitigative measures, and the performance plan.
• API Std 1104 (21st edition, 2013, with errata and addenda) for welding procedures, welder qualification and weld acceptance.
• ASME B31G (1991, reaffirmed 2004) for remaining-strength evaluation of corroded pipe in specified sections.

So the regulation can cite an older edition than the latest one ASME or API has published. B31.8 is now at 2025, and B31.8S has editions newer than 2018. Where an incorporated edition and the latest edition differ, the edition in 192.7 is what the regulation enforces. Operators may adopt newer editions in their own procedures where the regulation allows. Check 192.7 on the eCFR for the editions current on your inspection date.

The 2025 edition of B31.8 added a section on training and qualification of operating company personnel and a section on developing a damage prevention programme, according to ASME's product page. ASME's product page and the 2025 edition itself are the authoritative sources for those changes.

Class locations: why the same weld can need different NDT

B31.8 introduced the class location concept, and Part 192 uses it (192.5). A class location unit is an area extending 220 yards on either side of the pipeline centreline along any continuous one-mile length. Buildings for human occupancy within it are counted. Class 1 has 10 or fewer. Class 2 has more than 10 but fewer than 46. Class 3 has 46 or more, or the pipeline lies near certain buildings or outdoor areas where people gather. Class 4 is where buildings with four or more storeys above ground are prevalent. Class location drives design factors, test requirements and, for inspectors, the share of welds that must be examined.

Construction weld NDT under Part 192

For new construction and replacement work, the NDT requirements most inspectors look for are in 192.241 and 192.243:

• Visual inspection by an individual qualified by appropriate training and experience, to confirm the welding follows the procedure and the weld is acceptable.
• NDT is required on pipelines to be operated at a hoop stress of 20% or more of SMYS. There are two exceptions where welds visually inspected and approved by a qualified welding inspector need not be NDT'd: pipe under 6 inches nominal diameter, and pipelines operating below 40% SMYS where the welds are so few that NDT is impractical.
• Any NDT process except trepanning may be used if it clearly shows defects that may affect weld integrity. Radiography, manual UT, automated UT and encoded phased array are all used under API 1104 and the operator's procedures.
• Written procedures and trained, qualified personnel are required (192.243(b)). The operator must have procedures for interpreting results against the 192.241(c) acceptance standards.
• Minimum sampling of each day's field butt welds, selected at random: at least 10% in Class 1 locations, at least 15% in Class 2, and 100% in Class 3 and 4 locations, at specified crossings and within certain rights-of-way, unless impracticable, in which case not less than 90%. All tie-in welds must be tested. Each welder's work must be sampled daily where NDT is required.
• Records for the life of the pipeline showing, by milepost or other location reference, the number of girth welds made, the number tested, the number rejected and the disposition of each rejection (192.243(f)).

In-service inspection: Subpart O and ASME B31.8S

For gas transmission lines in high consequence areas, Part 192 Subpart O requires an integrity management programme. The elements most relevant to inspection are:

• Threat identification using the B31.8S framework, which groups threats by how they behave over time: time-dependent threats such as external and internal corrosion and stress corrosion cracking, stable threats such as manufacturing and construction defects, and time-independent threats such as third-party damage and weather.
• Baseline and continual assessment using in-line inspection (ILI), pressure testing, direct assessment (external corrosion direct assessment follows NACE SP0502), or other technology that gives an equivalent understanding of pipe condition.
• Reassessment intervals under 192.939, based either on the operator's threat analysis or, for pressure testing and ILI, on the stress-level-based intervals in B31.8S. Each covered segment must still be assessed within every 7 calendar years. Where the B31.8S-based interval is longer, confirmatory direct assessment can meet that 7-year checkpoint, and a single six-month extension is available on written notice with justification.
• Remediation of anomalies found, within the response timeframes in the rule. Operators confirm ILI calls and characterise anomalies at excavations ("digs").

Most field NDE in gas integrity work happens at the dig. Once the operator has exposed the pipe and cleaned the coating, technicians measure remaining wall and map corrosion over the anomaly area. They examine for cracking with magnetic particle testing where SCC or crack-like features are suspected, and they examine girth and seam welds within the excavation as the operator's procedure directs. Remaining-strength calculations, repair decisions and ILI tool performance assessment are the operator's, made by its integrity engineers.

Compressor and metering stations

B31.8 covers compressor station piping and metering and regulation stations as well as line pipe. Station piping sees vibration, small-bore connections, dead legs and changes in flow that are uncommon in cross-country pipe. The inspection work looks more like plant piping inspection: thickness surveys at fixed locations, corrosion mapping where loss is localised, and surface crack detection at small-bore connections and welded attachments. The governing requirements remain B31.8 and Part 192, applied through the operator's O&M procedures.

Offshore and sour gas

B31.8 has separate chapters for offshore gas transmission (Chapter VIII) and sour gas service (Chapter IX). Offshore adds splash-zone corrosion, risers and subsea access. Sour service adds hydrogen-related cracking risks, which affect material selection, welding and hardness control. For inspectors, sour service is where hardness testing and specific crack-detection techniques are more likely to appear in the operator's specification.

Canada: CSA Z662, not B31.8

In Canada, oil and gas pipeline systems are designed, built, operated and maintained under CSA Z662, which covers gas and liquid pipelines in one standard. It is enforced by the Canada Energy Regulator for federally regulated lines and by provincial regulators for provincial lines. A Canadian scope written "to B31.8" should be checked against Z662 and the regulator's requirements.

Common mistakes on B31.8 inspection scopes

For the wider picture of how ILI, direct assessment and dig NDE fit together, see the pipeline integrity inspection guide.

• Applying plant-piping acceptance criteria (ASME B31.3 or ASME Section VIII) to pipeline girth welds instead of API 1104 as adopted by Part 192.
• Assuming the newest editions of B31.8, B31.8S or API 1104 are what the regulation enforces, without checking 192.7.
• Getting the class location wrong and under-sampling welds.
• Recording dig measurements without tying them to the ILI feature, girth weld number and odometer or station reference, so the operator cannot use them to validate the ILI run.
• Treating the NDT report as the remediation decision. The operator's integrity engineer owns it.

How Atlantis supports B31.8 and Part 192 work

Atlantis performs field NDE for gas operators and their construction contractors. We examine girth welds to API 1104 using radiography or encoded PAUT where the project allows, plus surface methods. At excavations and above-ground sections we perform pipe-body thickness measurement, corrosion mapping and MT. ASNT-certified technicians work to the operator's procedures under ASNT Level III oversight. Atlantis does not run in-line inspection and does not make integrity, remaining-strength or repair decisions; those stay with the operator. See pipeline inspection services, pipeline radiography and pipeline ultrasonic testing.

Request a scope for B31.8 girth weld NDT, with a reply within one business day.

ASME B31.8 questions

What is the latest edition of ASME B31.8?

The 2025 edition. Note that 49 CFR 192.7 incorporates a specific earlier edition (currently 2018) for the sections that reference it.

What does ASME B31.8 cover?

Gas transmission and distribution piping systems, including pipelines, compressor stations, metering and regulation stations, gas mains, and service lines up to the outlet of the customer's meter set assembly.

What is the difference between B31.8 and B31.8S?

B31.8 is the design, construction and operation code. B31.8S is its non-mandatory supplement on managing system integrity, which Part 192 Subpart O adopts by reference for gas transmission integrity management.

What weld acceptance standard applies to gas pipeline girth welds?

For federally regulated gas pipelines, Section 9 or Appendix A of API Std 1104, per 192.241(c). Appendix A may not be used to accept cracks.

How many gas pipeline welds must be NDT'd?

Under 192.243, at least 10% of each day's field butt welds in Class 1, 15% in Class 2, and 100% in Class 3 and 4 and specified crossings (not less than 90% where 100% is impracticable), plus all tie-ins, subject to the exceptions in 192.241.

How often must gas transmission pipelines be reassessed?

Under 192.939, covered segments must be assessed within every 7 calendar years. Longer intervals based on B31.8S stress levels are allowed for pressure testing and ILI, provided a confirmatory direct assessment is done within the 7-year window.

How long must weld NDT records be kept?

For the life of the pipeline, under 192.243(f).

Does Atlantis perform in-line inspection?

No. Atlantis performs NDE on welds, at excavations and on station piping. ILI is run by specialist ILI vendors under the operator's programme.

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