Non-destructive testing (NDT) comprises a group of component testing techniques for evaluating the serviceability of a part without compromising its integrity. In principle, NDT tries to locate defects in a part's surface area that predict future failure prior to the part fails in service and without jeopardizing the part's energy.

Similar to fluorescent dyes, magnetic particle testing employs a layer of fine iron particles used to a momentarily magnetized part. Both liquid penetrant and mag particle testing use a quickly, low-cost ways of nondestructive flaw detection, they are both restricted to discovering the length and width of a defect.
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