What type of discontinuities are post emulsifiable penetrants typically sensitive to?

Post emulsifiable penetrants are typically sensitive to open, shallow discontinuities. The mechanism of post emulsifiable penetrant testing involves the application of a penetrant followed by a developer after an emulsifying agent is introduced. This process allows the penetrant material to remain in the pores and surface discontinuities, particularly those that are open and shallow. These types of discontinuities provide a path for the penetrant to enter and become trapped, creating a visible indication when the developer is applied.

Fine, tight cracks may not allow penetrants to enter effectively, as they are often too narrow for the penetrant to adequately fill. Large internal voids could be too deep or extensive to be detected effectively using the post emulsifiable method, as the penetrant may not reach the void’s interior. Therefore, the sensitivity of post emulsifiable penetrants is ideally suited for detecting open and shallow surface discontinuities, which explains why this is the correct choice.