Which material is not suitable for liquid penetrant testing?

Which material is not suitable for liquid penetrant testing?

• A. Metals
• B. Unglazed ceramics
• C. Plastics
• D. Glass

Answer: (B)

Liquid penetrant testing works best on clean, non-porous surfaces so the penetrant can enter only surface-breaking flaws and then be drawn out to reveal them with a contrast indicator. Unglazed ceramics are porous, with open pores that readily absorb penetrant into the bulk material rather than just into cracks at the surface. This causes excessive background staining and makes it difficult to distinguish real indications from the material’s own pores, leading to unreliable results. Metals, plastics, and glass generally offer non-porous or sealable surfaces that let the penetrant stay on the surface long enough to show flaws after excess penetrant is removed, producing clear, interpretable indications. Therefore, unglazed ceramics are not suitable for liquid penetrant testing.

Liquid penetrant testing works best on clean, non-porous surfaces so the penetrant can enter only surface-breaking flaws and then be drawn out to reveal them with a contrast indicator. Unglazed ceramics are porous, with open pores that readily absorb penetrant into the bulk material rather than just into cracks at the surface. This causes excessive background staining and makes it difficult to distinguish real indications from the material’s own pores, leading to unreliable results. Metals, plastics, and glass generally offer non-porous or sealable surfaces that let the penetrant stay on the surface long enough to show flaws after excess penetrant is removed, producing clear, interpretable indications. Therefore, unglazed ceramics are not suitable for liquid penetrant testing.