Penetrant Testing Interpretation, Evaluation, and Reporting
Interpretation versus evaluation
Interpretation is deciding what the indication is: relevant, nonrelevant, or false. Evaluation is judging a relevant indication against acceptance criteria. Candidates must separate these steps; questions often describe a technician who skips interpretation and rejects a part on a false indication.
Indication sources
Relevant indications arise from actual discontinuities. Nonrelevant indications come from geometry (joints, threads, keyways, rough surfaces) that trap penetrant. False indications come from contamination, poor cleaning, developer artifacts, or handling. Fluorescent bleed-out from a porous surface is a classic nonrelevant case.
Sizing and characterization
Indications are characterized by type (linear, rounded, aligned, etc.), length, and location. Linear indications are typically defined by a length-to-width ratio (commonly 3:1 in many codes). Aligned indications are evaluated as a group per the code's spacing rules.
Traps
- Confusing linear and rounded definitions; check the code's ratio.
- Treating a nonrelevant indication as rejectable without confirming it is a discontinuity.
- Ignoring indication location relative to critical areas or weld toes.
- Reporting without recording light conditions and technique, which are needed for traceability.
Worked example
A fluorescent indication measures 4 mm long and 1 mm wide. Length-to-width is 4:1, so it is linear under a 3:1 rule. If the code rejects linear indications over 1.5 mm in the weld toe, the part is rejected. If the same indication were 4 mm by 2 mm (2:1), it would be rounded and judged by the rounded criteria.