Flaw — Definition & NDT Use
A discontinuity or defect in material that may affect its service capability. The term "flaw" is sometimes used interchangeably with "defect" and "discontinuity," though flaws specifically refer to undesirable discontinuities that exceed acceptance criteria. In NDT, the goal is to detect all flaws of sufficient size and type to warrant repair or rejection. Flaw characterization and sizing are critical for fitness-for-service assessment.
In service, Flaw starts as a discontinuity that may or may not breach the acceptance criteria of the governing code; the NDT method's job is to detect it, characterise it, and size it so an engineer can decide whether to repair, monitor, or accept. The fitness-for-service decision typically pairs the NDT call with material data and stress information; the inspector's job is to give the engineer a clean characterisation rather than to make the keep-or-reject call alone.
The decision tree around Flaw runs: detect, characterise, size, and refer to the acceptance table in the governing code; only the last step decides repair, accept-as-is, or fitness-for-service review.
Confusing flaw with a generic "indication" is a recurring error; the term carries an engineering implication, and the report should distinguish the discontinuity (what was seen) from the disposition (what code says about it).
What does "Flaw" mean in NDT?
A discontinuity or defect in material that may affect its service capability. The term "flaw" is sometimes used interchangeably with "defect" and "discontinuity," though flaws specifically refer to undesirable discontinuities that exceed acceptance criteria
Is flaw always rejectable?
No. Whether a flaw indication is rejectable depends on the acceptance criteria of the governing code (AWS D1.1, ASME Section VIII, API 1104, etc.), the size and orientation of the indication, and any fitness-for-service evaluation the engineer chooses to apply.
What other NDT concepts should I read alongside Flaw?
The most directly related entries in this glossary are "defect", "discontinuity", "indication"; reading those together gives you the surrounding vocabulary used in inspection reports and procedures.