The MPI process is used for detecting surface and near surface indications in ferromagnetic materials. The process uses inks: paints and electro and permanent magnets.

The method involves the application of white background paint on the area under examination. Once dry, an electromagnet or permanent magnet is applied across the weld axis or component axis and energised. Once energised a black magnetic ink is applied. The carrying ink holds very fine magnetic particles which are attracted to flux leakage fields for example cracks and lack of fusion. As a result of the process, these types of flaw show up visually as a black indication on a white background.

Other MPI processes include: fluorescent inks and blacklight (UV). Once indications are found they are evaluated against the relevant standards/acceptance criterias.

Magnetic Particle inspection standards mainly used are;

ISO 17638 Non- destructive testing of welds – Magnetic Particle testing

ISO 23279 Non- destructive testing of welds – Magnetic Particle testing of welds –Acceptance levels

ISO 9934-1 Non-destructive testing – Magnetic particle testing – Part 1: General principles
ISO 9934-2 Non-destructive testing – Magnetic particle testing – Part 2: Detection media
ISO 9934-3 Non-destructive testing – Magnetic particle testing – Part 3: Equipment

Other standards can be worked to and procedures written in accordance with.

Magnetic Particle Inspection