Quality Control of Drying Process
The temperature used to dry parts after the application of an aqueous wet developer or prior to the application of a dry powder or a nonaqueous wet developer, must be controlled to prevent "cooking" of the penetrant in the defect. High drying temperature can affect penetrants in a couple of ways. First, some penetrants can fade at high temperatures due to dye vaporization or sublimation. Second, high temperatures can cause the penetrant to dry in the the flaw, preventing it from migrating to the surface to produce an indication. To prevent harming the penetrant material, drying temperature should be kept to under 71oC.
The drying should be limited to the minimum length of time necessary to thoroughly dry the component being inspected.