Dye penetrant inspection (DPI) is a non-destructive testing method used to reveal surface breaking flaws by bleedout of a coloured or fluorescent dye from the flaw. DPI is one of the most widely used non-destructive testing methods, because it can be used to inspect almost any material provided that its surface is not extremely rough or porous; it is relatively easy to perform and can be used in a lab or in the field.
Magnetic particle inspection (MPI) uses magnetic fields and small magnetic particles (i.e. iron filings) to detect flaws in ferromagnetic components. It is fast and relatively easy to apply and can also be used in a lab or in the field.