Magnetic Particle Testing Methods Explained

Magnetic Particle Testing (MPT), also known as Magnetic Particle Inspection (MPI), is a non-destructive testing (NDT) method used to detect surface and near-surface flaws in ferromagnetic materials. The process involves magnetizing the part and then applying iron particles (either dry or suspended in a liquid). If a flaw exists, it disrupts the magnetic field, causing the particles to gather around the discontinuity, thus indicating the location and severity of the flaw.

Common Magnetic Particle Techniques

Several techniques are employed in MPT to induce the necessary magnetic field in the part being inspected. These include:

• Prod Technique: This method uses two prods (electrodes) placed on the surface of the part. When current flows between the prods, it creates a magnetic field (usually circular) in the area between them. This is effective for localized inspection areas.
• Coil Technique (Coil Shot): In this technique, the part is placed inside a coil, or a coil is wrapped around the part. An electric current flowing through the coil generates a longitudinal magnetic field within the part. This is often used for inspecting long parts like shafts or bars.
• Yoke Technique: A yoke, which is essentially a portable electromagnet with two poles, is used to establish a magnetic field across a specific area of the part. The poles of the yoke are placed on the surface, and the magnetic field flows between them. This technique is versatile for inspecting various shapes and sizes.

Identifying Non-Standard MPT Methods

Among the options provided, the "Plate technique" is not recognized as a standard method for inducing a magnetic field in magnetic particle testing. While a plate might be used as a component or fixture during the inspection process (e.g., a surface plate for positioning), it does not represent a method of generating the magnetic field required for the MPT process itself.

Therefore, the technique that is NOT a type of magnetic particle testing method is the Plate technique.