Which of the following tests is used to check for surface defects?

The magnetic particle test is specifically designed to detect surface and near-surface defects in ferromagnetic materials. This non-destructive testing method involves the application of a magnetic field to the surface of the material being tested. A ferromagnetic powder, either dry or suspended in liquid, is then applied to the surface. Any surface or near-surface flaws will disrupt the magnetic field, causing the powder to cluster and form a visible indication of the defect. This makes the magnetic particle test highly effective for identifying cracks, seams, laps, and other discontinuities that are not easily visible, thus ensuring the integrity and safety of the material being evaluated.

Other methods, such as visual inspection, can also identify surface defects but generally rely on the inspector's ability to see the defects without the aid of particles or additional materials. The radiographic test is used primarily to detect internal flaws rather than surface defects, as it involves the use of X-rays or gamma rays to examine the internal structure of materials. Therefore, while visual inspection can catch some surface defects, the magnetic particle test offers greater sensitivity and accuracy in identifying them specifically.