In penetrant testing, how can one ascertain that a crack is open and detectable?

In penetrant testing, ascertaining whether a crack is open and detectable involves assessing the ability of a penetrant material to enter and fill the discontinuity. The correct approach is to apply pressure to the test component. When pressure is applied, the crack will open slightly, allowing penetrant material, which may have been too thin or sealed prior to the pressure application, to enter the crack. After releasing the pressure, one can observe whether the crack has filled with penetrant, indicating an open and detectable discontinuity.

This method ensures that any tight cracks or defects that may not be visible without additional intervention can be properly evaluated, thus making it a reliable technique for assessing the integrity of materials being tested. This process is crucial in penetrant testing because it allows for a more accurate determination of the presence and extent of any potential defects.