The serviceability of the flaw-detecting materials
used in these methods is conventionally checked with the aid of various types of flat specimens, e.g., specimens
made of austenitic chromium–nickel steel with star-type cracks in the chromium coating; specimens
of corrosion-resistant 40Kh13 martensitic steel with single cracks; brass specimens with straight cracks in
the layer of nickel–chromium coating; etc