Distinguish the visible line from the target

A coating crack, an intended surface feature and a deeper defect may all create different inspection questions. Penetrant response at the outer surface cannot independently establish how far a feature extends beneath it. ASNT describes the method as surface-only and unsuitable for porous materials. That limitation matters if a damaged or exposed blade surface no longer behaves like an intact nonporous coating.

Consider preparation and contamination

Cleaning agents, penetrant and developer contact the actual surface and can enter an open feature. They must be compatible with the relevant coating, resin and any planned repair process. Improvised application can obscure evidence or introduce material that complicates later assessment. The responsible specialist should determine suitability, preparation and interpretation under an approved procedure; this page gives no application sequence or field test instructions.

A penetrant indication through a surface coating can locate an open feature without revealing whether its underlying path continues into reinforcement. The report should avoid turning that surface finding into an unsupported depth measurement or a whole-blade structural classification without complementary evidence.

Choose evidence for the structural question

Ask what result the proposed method can establish and what deeper concerns it leaves unanswered. If internal damage remains plausible, a suitable complementary examination may be required. A negative surface indication does not automatically mean the blade is undamaged, and a positive indication still needs qualified evaluation. No MARSTON blade penetrant compatibility, crack acceptance limit or repair method is asserted here; the actual construction and responsible reviewer must govern.