Magnetic particle inspection is a nondestructive testing method which can be used in the evaluation of all ferrous materials. Like other forms of nondestructive testing, this method has the advantage of not damaging or compromising the materials being tested during the testing process. This method is one of the fastest and least expensive ways to test ferrous materials before certifying them as safe and ready for use.
In a magnetic particle inspection, the object being tested is surrounded by a magnetic field. Particles suspended in a carrier fluid are sprayed onto the object. If there is a defect in the object, it will cause a corresponding distortion in the magnetic field which will be readily visible as particles are pulled towards the distortion. If there are no defects, the particles should remain evenly distributed.
Ferrous metals at a variety of stages of production can be subjected to magnetic particle inspection to check for fatigue cracks, pitting, and other problems. This testing can be used to evaluate finished parts and products before they are released to the market in addition to being used in the inspection of slabs of raw materials to check for flaws which could compromise future performance.
Ferrous metal parts in service can also be inspected with the use of this technique. Equipment, such as aircraft and manufacturing parts, needs to be routinely inspected to check for signs of fatigue, strain, and other issues, to confirm that it is safe for use. Magnetic particle inspection is one technique which can be used during an inspection. If a part or machine fails the inspection test, it indicates that additional work is needed to render it safe.
Dyes can be added to the particles to make them easier to see, including dyes which will react to ultraviolet light. With ultraviolet-sensitive particles, testers can conduct a magnetic particle inspection under UV light and clearly visualize the distribution of the particles. The highlighted particles will also photograph well, allowing people to create easily-read documentation of inspection results.
There are other inspection techniques available to evaluate ferrous metals. Some of these techniques may be used in addition to magnetic particle inspection for a complete inspection, while others may be used instead in some circumstances. All of these techniques require extensive training in nondestructive testing to confirm that they are conducted properly. If a test is done wrong, a false negative result may be obtained, leading people to believe that something is safe when it is not.