Porosity — Definition & NDT Use

In service, Porosity 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. Radiation passes through the part and a dense region (more material, more attenuation) records as a lighter band on film or digital detector, while a void, lack of fusion, or porosity records as a darker area; an image quality indicator (IQI) verifies that the technique was sensitive enough to be trusted. 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 Porosity 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. On welded fabrication it is most often paired with VT and one volumetric method (RT or UT) so surface and internal defects are both addressed.

Confusing porosity 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).