There are different methods used in Non-destructive testing. Today, we will discuss one of the efficient flaw detection methods in magnetic materials – Magnetic Particle Inspection. 

Magnetic particle inspection, or MT or MPI, is a non-destructive inspection method that helps to detect surface and subsurface flaws on ferromagnetic materials. It is primarily used as a surface examination technique.

This is a crucial topic in the oil and gas courses for mechanical engineers.

Basic Principle of Magnetic Particle Inspection

Magnetic Particle Inspection is carried out using a basic principle which we will discuss here. If you’re opting for any online course in piping engineering, you must have the fundamentals of these topics very clear.

According to the principle, the specimen is magnetized to produce magnetic lines of force, or flux, in the material. When these lines meet at a discontinuity, such as a crack, you will find secondary magnetic poles created at the faces of the crack. 

If these secondary magnetic fields appear at the surface of the metal, you can identify them by applying magnetic particles, as a powder, or in a liquid suspension, to the surface. 

The particles are basically attracted to the flux leakage and gather around the flaw, making it visible. To increase their visibility, the particles may be black or coated with a fluorescent dye.

You need to understand various terms used while implementing the basic principle. 

Advantages & Disadvantages of Magnetic Particle Inspection

Now, let’s see the advantages and disadvantages of MT or MPI.

Advantages

It is a quick and not so complicated process

It provides immediate flaw detection.

It helps to identify the surface and near-surface defects

It is inexpensive compared to radiography.

Disadvantages

It works only on ferromagnetic materials – usually iron and steel, and you cannot detect flaws on austenitic stainless steel.

It is sometimes difficult to determine if the magnetic field is sufficiently strong to give better indications.

The method cannot be used on parts with a thick coat of paint.

Most of the methods need electricity supply for the inspection.

There are many more aspects to magnetic particle inspection. We will discuss it as a part of oil and gas training courses online in the upcoming blogs. Till then, stay tuned for more interesting updates and keep checking our blog section.