Non-Destructive Testing (NDT) Practice Test

What angle must the magnetic field intercept a defect in a test piece to effectively detect it?

1. 0 to 30 degrees

2. 30 to 60 degrees

3. 45 to 90 degrees

4. 90 to 120 degrees

The correct answer is: 45 to 90 degrees

The effectiveness of magnetic particle testing, a form of NDT, significantly relies on the angle at which the magnetic field intercepts a defect within the test piece. An angle in the range of 45 to 90 degrees is fundamental because this orientation allows the magnetic field lines to effectively penetrate the defect and produce a noticeable flux leakage. This leakage creates a detectable indication of the defect's presence, as it causes the magnetic particles to accumulate at the surface, forming a clear indication for the inspector. When the magnetic field is at an angle that is either too shallow (0 to 30 degrees) or too acute (90 to 120 degrees), the likelihood of detecting the defect diminishes. In shallow angles, the magnetic flux may not effectively interact with the defect, while at very steep angles, the field may not generate sufficient magnetic leakage for the particles to accumulate. Thus, ensuring that the magnetic field is appropriately oriented between 45 and 90 degrees is critical for reliable defect detection during magnetic particle testing.