After the workpiece has been cleaned, liquid penetrant is applied in a suitable manner so as to form a film of the penetrant over the surface for at least 13mm beyond the area being inspected.

The water based dye penetrant is too low in sensitivity to inspect the vessels for cryogenic liquid oxygen.

Regardless of the type penetrant used, and regardless of other variations in the basic process, liquid-penetrant inspection requires at least five essential steps.