Standards for Magnetic Particle and Liquid Penetrant Inspection
Magnetic particle and dye penetrant inspections should conform to the following:
Indications of themselves shall not be cause for rejection unless so specified by the customer.
At the time of inspection the nature of the discontinuities shall be determined and placed on one or more of the following categories:
a. Propagating indications
b. Nonpropagating indications
c. Dispersed indications
Propagating indications are those which conceivably could increase in length or width under stress, resulting in failure of the part. In this category would fall such indications as cracks, hot tears, segregation, pits, holes, or other imperfections so aligned as to be propagating in nature.
Nonpropagating indications are discrete, usually rounded indications. This category would include gas holes, holes resulting from air entrapment, dross holes, inclusions, pits, and other surface imperfections.
Dispersed indications are those which are nonpropagating in nature, but are distributed over a larger area of the casting. In this category would fall sponge and microshrinkage (generally found only in aluminum and magnesium castings), gas porosity, and other surface indications.
Source: Investment casting Institute Handbook 1997 Edition