Which method is NOT a commonly accepted method for applying penetrant?

Heating the penetrant is not a commonly accepted method for applying penetrant. The standard methods for applying penetrant include pouring, dipping, and spraying, all of which allow for even coverage and penetration into the cracks or voids of the material being inspected. Each of these methods is designed to ensure that the penetrant adequately fills any defects that may be present.

Pouring allows for a controlled application of the penetrant over a surface, ensuring that it can seep into small cracks. Dipping is effective for immersing the entire part in the penetrant, guaranteeing thorough coverage. Spraying can provide a fine mist, allowing for uniform distribution over complex or irregular surfaces.

Heating the penetrant, however, is not a recognized technique because it can affect the viscosity and properties of the penetrant, potentially leading to improper application and inadequate penetration. This could result in missed defects during inspection, compromising the reliability of the testing process. Hence, method C stands out as the one that does not fit within the standard practices used for applying penetrants in non-destructive testing.