Magnetic particle inspection is a nondestructive evaluation process used to detect linear flaws in tanks and vessels. Magnetic Particle Inspection, or MT or MPI, is a surface examination method popular amongst API inspection companies. One can detect sub-surface defects like cracks, cold lap, sidewall fusion, pore, and surface breaking in magnetic materials through magnetic particle inspection.
In this blog, we have covered some essential aspects of magnetic particle inspection.
How is magnetic particle inspection conducted?
There are two ways for conducting magnetic particle testing – Dry Magnetic Particle Testing and Wet Magnetic Particle Testing.
A handheld electromagnetic yoke magnet, white strippable paint, and magnetic ink are used in one of the most common methods. In both the test, a magnetic current is passed through the testing surface. Metal particles are spread over the tested surface of the tank or the vessel. In the presence of any defect in the material or surface, the magnetic current flow gets interrupted, causing a flux leakage field to appear. In the next step, the magnetic particles’ groupings are analyzed to assess the degree and extent of the damage. Once the testing is complete, the area is demagnetized and cleaned.
Precautions to be taken when conducting Magnetic Particle Inspection
When performing magnetic particle inspection, the magnetic particles should have a clear path to move around the weak and strong leakage fields. The entire surface should be clean and dry. The presence of grease and other contaminants may prevent the particles from attracting to the leakage fields and affect the results’ accuracy.
Advantages of Magnetic Particle Inspection
Like most other nondestructive inspection methods, magnetic particle testing is inexpensive and reliable. There is no pre-clean-up protocol that makes the test easy to perform. Magnetic particle testing is preferred by API inspection services providing professionals as it perfectly detects cracks in the shallow surface.
- Magnetic particle inspection can be used to detect flaws on the surface and sub-surface.
- Magnetic particle tests are affordable and portable.
- MPT is a rapid inspection method that offers accurate results in a quick time.
- MPT offers direct indications of defects which makes it easier for the inspector to check and remedy.
- MPT is also effective in detecting flaws on irregular shapes and surfaces. Crankshafts, external splines, and connecting rods can be checked through MPT.
Limitations of Magnetic Particle Inspection
Although there are countless advantages of magnetic particle inspection, there are some limitations to this testing methodology. For instance, the material being tested must be ferromagnetic like cast iron, steel. One of the essential factors in MPT is the strength and orientation of the magnetic field. Magnetic particle testing can only detect flaws present on the surface or sub-surface area.
Alternative testing methods are required to detect flaws that are present beyond the surface. Often large electromagnetic currents are necessary to perform the test. The use of a large current may sometimes lead to the burning of the specimen. After performing magnetic particle inspection, the area should be demagnetized. The demagnetizing process can get complicated if a large area is tested.