NDT Codes & Standards: Which One Governs Your Inspection

Three kinds of document

It helps to sort NDT standards into three roles. Method/technique standards say how an examination is carried out — ASME Section V is the anchor, defining radiography, ultrasonics, MT, PT and more. Acceptance/construction codes say what is good enough at build — ASME Section VIII for vessels, B31.3 for process piping, AWS D1.1 for structural steel. In-service inspection codes say when and how often to re-inspect operating equipment — the API 5xx family and risk-based inspection (RBI).

A single weld can touch all three: examined per ASME V, accepted per ASME VIII at construction, then re-inspected on an interval set by API 510 once the vessel is in service. Knowing which document drives which decision is half of getting the procedure approved.

The in-service inspection codes (API 5xx)

For operating plant, the API in-service codes set the inspection program. Each covers a class of equipment and points back to NDT methods for thickness, cracking and damage-mechanism detection.

The method standard: ASME Section V

ASME Section V is the technique rulebook referenced by most construction codes. Its articles define how each examination is performed — Article 2 (radiography), Article 4 (ultrasonics, including encoded PAUT and TOFD appendices), Article 6 (penetrant), Article 7 (magnetic particle), Article 9 (visual). When a construction code says "examine per Section V", it is Section V that sets calibration, technique and documentation, while the construction code keeps the acceptance criteria.

From damage mechanism to method

The most efficient inspection programs start from the credible damage mechanism, not a blanket scan. API 571 catalogues mechanisms — thinning, environmental cracking, high-temperature degradation, mechanical fatigue — and each points to the method that detects it. Sulfidation thinning is a UT-thickness problem; chloride stress-corrosion cracking needs surface methods or PAUT; high-temperature hydrogen attack (HTHA) calls for advanced UT/TOFD and velocity-ratio techniques. RBI (API 580/581) then turns that mechanism-and-consequence picture into a scope and an interval, so high-risk circuits get more NDT and low-risk circuits get less.