6.1 NDE Methods, Acceptance Criteria & Documentation

6.1 NDE Methods, Acceptance Criteria & Documentation

Quick Answer: Non-destructive examination (NDE) verifies that girth welds are sound without destroying the pipe. On pipeline construction the inspector confirms that the right method — RT, UT (including AUT/PAUT), MT, PT, or VT — is applied per the approved procedure by qualified personnel (ASNT SNT-TC-1A / NAS 410, Level II+), at the coverage the project requires, and that every NDE report maps back to the weld map. Indications are dispositioned against API 1104 acceptance criteria as accept, repair, or cut-out.

The Five NDE Methods Used on Pipeline Welds

NDE is part of API 1169 Body of Knowledge Area 3 — Installation Construction, the largest BOK area (an unofficial practice-weighted estimate near 36%). Each method finds a different family of discontinuities, and the project specification dictates which methods and coverage apply.

When Each Method Is Specified

• VT is mandatory on every weld before any other method — the inspector checks cap profile, undercut, reinforcement height, and hi-lo visually.
• RT has been the historical default for girth-weld inspection; project specs call for 100% RT on mainline, crossings, and tie-ins, or a random percentage (commonly 10%) on low-stress areas.
• AUT/PAUT is now widely used on large-diameter, high-stress pipelines because it is faster, produces a stored coded image, and avoids radiation exposure; the project spec and NDE procedure define whether UT replaces or supplements RT.
• MT is applied to surface weld toes and to the pipe body near welds where surface cracks are suspected (e.g., hard spots, arc burns).
• PT is reserved for non-ferromagnetic materials or where MT equipment cannot be used.

API 1104 Acceptance Criteria for Weld Discontinuities

API 1104 (22nd Edition) Section 9 — Acceptance Standards for Nondestructive Testing gives the acceptance standards the inspector applies to NDE indications. (Section 8 covers Inspection and Testing of Production Welds — who may inspect and by what method; Section 9 holds the numbers.) A discontinuity is an interruption in the weld; it becomes a defect only when it exceeds the acceptance criteria. The table below summarizes the common indications and their typical disposition.

Disposition of Indications

When NDE finds an indication, the inspector confirms it is evaluated against the acceptance criteria and one of three dispositions is assigned:

1. Accept — the indication is within limits; the weld is recorded as accepted and no further action is taken.
2. Repair — the defect is ground out and re-welded under a company-authorized repair procedure per API 1104 Section 10 (a repair of an already-repaired area needs specific company authorization), then re-examined by the same NDE method to the same standard.
3. Cut-out — the defect cannot be repaired within limits (cracks, deep/long defects, or a third failed repair); the weld or joint is cut out and replaced as a new production weld.

NDE Personnel and Procedure Qualification

Personnel Qualification

NDE must be performed by qualified personnel. The industry references are ASNT SNT-TC-1A and NAS 410 (the aerospace-derived standard adopted by many pipeline operators). For API 1169 work, the examiner who performs and interprets the inspection is typically Level II or higher; Level I may operate under supervision but does not interpret. The inspector verifies:

• Certification records on site — Level II certificates in the method being used (RT, UT, MT, PT).
• Personnel are qualified in the specific method — a Level II in RT is not automatically qualified to interpret AUT; qualification is method-specific.
• Vision requirements current — near vision and color contrast, typically verified annually.

Procedure Qualification

Each NDE method must be performed per an approved, qualified procedure:

• RT procedure — source-to-film distance, exposure time, film type, IQI (penetrameter) sensitivity, and density.
• AUT/PAUT procedure — calibration block, scanning pattern, encoding, sensitivity setting, and demonstration on a weld with known defects before production use.
• Coverage — the procedure and project spec define whether inspection is 100% of the weld length or a sampled percentage; the inspector verifies the required coverage was actually performed and documented.

Report-to-Weld-Map Traceability

Every NDE report must tie back to the weld map. The inspector verifies:

• Weld ID and station on the NDE report match the weld map entry.
• Result — accepted, rejected, or repair — is recorded on both the NDE report and the weld map.
• Repair and re-NDE — the repair location, method, welder, and re-examination result are logged.
• Reject/repair log maintained so the total repair rate can be tracked — a high repair rate flags a welding-procedure or welder problem that the company representative must address.

A missing or mismatched NDE report is a documentation finding; without it, traceability of the finished pipeline is broken.

Radiographic Safety

When RT is used, the inspector verifies radiographic safety controls:

• Radiation safety officer / qualified RT technician on site.
• Barrier and signage — exclusion zone set up, signs and barriers in place, dosimetry worn.
• Source control — iridium-192 or selenium-75 source stored, transported, and exposed per regulation; source logs current and the source is accounted for at the end of each shift.
• No personnel in the exclusion zone during exposure.

Key Takeaways Recap

• VT is the first and mandatory NDE on every weld; RT and UT/AUT are the primary volumetric methods.
• API 1104 Section 9 gives the acceptance criteria; any crack is rejectable, while porosity, slag, undercut, and reinforcement have size/depth/height limits.
• NDE personnel must be Level II+ certified in the method, per SNT-TC-1A / NAS 410.
• Every NDE report maps to the weld map by weld ID, station, and result; disposition is accept, repair, or cut-out.
• RT requires radiation safety — exclusion zone, signage, source control, and dosimetry.