Magnetic Particle Testing Technique
Magnetic particle testing (MPT) is a non-destructive testing method that detects surface and subsurface defects in ferromagnetic materials, such as iron and steel. The technique involves applying a magnetic field to the test object, and then introducing a fine powder, called magnetic particles, which are attracted to areas of magnetic flux leakage caused by defects. The particles can be visible (such as iron filings) or fluorescent, and are usually applied wet to enhance visibility. MPT is commonly used in the aerospace, automotive, and oil and gas industries to inspect welds, castings, and other components for cracks and other types of defects.
MPT can be performed in two ways: dry and wet. In the dry method, a dry powder of magnetic particles is dusted over the surface of the test object and a magnetic field is applied. In the wet method, the magnetic particles are suspended in a liquid and applied to the surface of the test object with a brush or spray gun. The wet method is more sensitive and provides better visibility of defects than the dry method.
The test object is first magnetized by applying a magnetic field. This can be done by using a direct current (DC) electromagnet, a low-frequency alternating current (AC) magnet or a high-frequency AC yoke. Once the object is magnetized, the magnetic particles are applied to the surface of the test object, and the defects will cause the particles to cluster and form visible indications. These indications can then be examined to determine the size, shape, and location of the defect.
MPT is a cost-effective and efficient method for detecting surface and subsurface defects in ferromagnetic materials. It is also a highly portable method that can be used in the field as well as in a laboratory setting. However, it is not suitable for non-ferromagnetic materials such as aluminum, brass, and stainless steel.
Overall Magnetic particle testing (MPT) is a powerful and versatile method for detecting surface and subsurface defects in ferromagnetic materials, and it is widely used in many industries including aerospace, automotive, and oil and gas.
In addition to being used to inspect welds, castings and other components, Magnetic Particle Testing (MPT) is also used to inspect raw materials and finished products, such as bars, billets, plates, forgings, and gears. It can also be used in combination with other NDT methods such as radiography, ultrasonics, and liquid penetrant testing for more thorough inspection.
One of the advantages of MPT is that it does not require special surface preparation or cleaning before the test, which makes it a fast and easy method to use. Also, it can detect both surface and subsurface defects, as well as defects that are not visible to the naked eye.
Another advantage of MPT is that it can be used to inspect both ferromagnetic and non-ferromagnetic materials. For non-ferromagnetic materials, a magnetic field is induced by applying a current to a coil wrapped around the material.
There are different types of MPT methods, like DC magnetic particle testing, AC magnetic particle testing and HFLW AC Magnetic particle testing.
DC Magnetic Particle Testing is used for detecting surface breaking defects. It is used for detecting defects in ferromagnetic materials.
AC Magnetic Particle Testing is used for detecting both surface breaking and subsurface defects. It is used for detecting defects in ferromagnetic materials.
HFLW AC Magnetic Particle Testing is used for detecting both surface breaking and subsurface defects. It is used for detecting defects in both ferromagnetic and non-ferromagnetic materials.
Overall, Magnetic Particle Testing is a versatile and efficient NDT method that can be used to detect a wide range of defects in ferromagnetic and non-ferromagnetic materials. It is a cost-effective and efficient method that is widely used in many industries.