Residual Magnetisation Technique

The residual technique is a testing technique where the magnetic ink or powder is applied, and the test area is viewed after the magnetising force has been removed. The test is performed using the residual magnetism left in the sample. This technique is generally only used on materials with a high retentivity/low permeability. When multiple items are being tested by the residual technique, care must be taken to ensure that the components do not come into contact with each other before the detecting media is applied, otherwise a phenomenon known as ‘magnetic writing’ will occur.
Residual magnetisation is generally used when there are geometric restraints, such as restricted access.