This method is used to test welds, castings, and forgings for defects; however, it can only be used on ferromagnetic metals, such as iron, nickel or cobalt and some of their alloys. The process puts a magnetic field into the part and the piece is magnetised by direct or indirect magnetisation. The presence of a surface or subsurface discontinuity in the material allows the magnetic flux to leak.
Identity of a leak, ferrous particles are applied to an object, these are attracted to an area of flux leakage and form what is known as an indication. Indications are evaluated to determine its nature and cause.
- It is quick and relatively uncomplicated.
- It gives immediate indications of defects.
- It shows surface and near surface defects, and these are the most serious ones as they concentrate stresses.
- The method can be adapted for site or workshop use.
- It is inexpensive compared to radiography.
- Large or small objects can be examined.