Which statement best states the danger of sandblasting (without subsequent chemical etching) for cleaning surfaces to be penetrant tested?

Which statement best states the danger of sandblasting (without subsequent chemical etching) for cleaning surfaces to be penetrant tested?

• A. Causes corrosion
• B. The discontinuities may be peened over and closed
• C. The surface may warp
• D. Abrasive residues may remain

Answer: (B)

In penetrant testing, the surface condition must allow penetrant to enter any surface-breaking flaw. Sandblasting before testing can physically deform and roughen the surface, creating compressive residual stresses that can peen over and close small discontinuities. When cracks or flaws are closed, the penetrant cannot seep into them, so they may not be detected and the part could be falsely deemed acceptable. Chemical etching after cleaning helps reveal defects by removing surface films and enhancing entry pathways, so skipping etching keeps that closing risk in play. While corrosion, warping, or residues can matter in other contexts, the primary danger here is that discontinuities may be closed by the peening action, hiding defects.

In penetrant testing, the surface condition must allow penetrant to enter any surface-breaking flaw. Sandblasting before testing can physically deform and roughen the surface, creating compressive residual stresses that can peen over and close small discontinuities. When cracks or flaws are closed, the penetrant cannot seep into them, so they may not be detected and the part could be falsely deemed acceptable. Chemical etching after cleaning helps reveal defects by removing surface films and enhancing entry pathways, so skipping etching keeps that closing risk in play. While corrosion, warping, or residues can matter in other contexts, the primary danger here is that discontinuities may be closed by the peening action, hiding defects.