A continuous linear indication in penetrant testing typically indicates which type of discontinuity?

In penetrant testing, a continuous linear indication is most indicative of cracks. This type of indication occurs when the penetrant dye seeps into surface openings that are linear in nature, which is characteristic of crack formations. Cracks can often be very thin and linear, allowing the penetrant to fill them effectively, leading to a clear visual signal once the excess penetrant is removed and the development process is applied.

Other types of discontinuities, such as porosity, weld defects, or corrosion, typically present different characteristics. For example, porosity would generally manifest as clustered or scattered indications rather than continuous linear ones. Weld defects often encompass a broader range of discontinuities that can be more irregular in shape. Corrosion, while it may sometimes cause cracks, usually results in more diffuse indications and irregular patterns rather than linear ones. Thus, the nature of the indication—specifically its continuity and linearity—makes it a clear signal of cracking in penetrant testing.