Magnetic particle testing is a non-destructive testing method for detection of imperfections on or just below the surface of ferrous metals. It is a quick and reliable technique for detection and location of eg. surface cracks.
A magnetic flux is send through the material. At the location of the imperfection a leakage field is formed. This attracts metal iron dust, which is sprayed onto the surface. The length of the imperfection can be determined very reliable. Magnetic particle testing does not indicate the depth of the imperfection. Acceptance criteria define whether or not the indication is non-acceptable (a defect) or not.
Magnetic particle testing can be used for all ferrous metals, such as carbon steel, low-alloy and cast iron. The main use of Magnetic particle testing is for welds and heat affected zones. It can be applied to relatively rough and dirty surfaces but flaw sensitivity is decreased for this. Fluorescent particles can be used when maximum sensitivity is required.