Porosity is a volumetric discontinuity associated with gas cavities in weld metal. On a radiograph, a cavity may appear as a rounded area with greater film density than the surrounding sound material because less material attenuates the radiation along that path. This is a general teaching description, not a diagnosis from appearance alone.
Patterns can vary
Gas cavities may be isolated, grouped, distributed, or elongated depending on their shape, orientation, size, location and the projection geometry. Small or closely spaced cavities can merge visually. Thickness changes, weld profile, superimposed features, film contrast and exposure conditions also influence what is visible. A radiograph is a two-dimensional projection, so depth and shape are not always obvious.
Do not confuse appearance with acceptance
A rounded indication is not automatically porosity, and a porosity-like appearance does not by itself establish its origin or severity. Review component location, weld geometry, the specified examination technique and other relevant information. Distinguish the observed indication from the interpretation and from the final evaluation against acceptance criteria.
Use the job’s evaluation rules
Applicable acceptance rules can depend on material, product form, joint type, service, contract and governing code. They may consider dimensions, distribution, number, spacing or cumulative length in a defined evaluation area. This article gives no universal reject limits. Use only the criteria specified for the job and the examiner’s approved authority. If the image is ambiguous or its quality is insufficient, document the limitation and follow the approved escalation or additional-examination process.
Useful review questions
- Is the indication within the weld or another geometric feature?
- Does its shape and distribution remain consistent across available views?
- Are image quality and IQI requirements satisfied?
- Could processing, handling or screen contact have produced an artifact?
- Which acceptance document and revision govern this examination?
Radiographic interpretation is a qualified activity. Indication appearance is affected by geometry and technique; only the governing project requirements determine acceptance.