Magnetic particle MT flaw detection is a commonly used non-destructive testing method, mainly used for cracks, pores, inclusions and other defects of API 5L carbon steel oil pipelines. It uses the working principle of magnetic field and magnetic powder. By applying a magnetic field on the surface of the material to be inspected, the magnetic powder is adsorbed at the defect, thereby showing the location and shape of the defect.
The main steps of magnetic particle MT flaw detection are as follows:
1. Pretreatment: First, clean the material to be inspected and remove impurities such as oil to ensure the accuracy of the test results. Then, grind and polish the surface of the material to be inspected to facilitate the adsorption and display of magnetic powder.
2. Magnetization: Place the material to be inspected in a strong magnetic field to make it magnetic. There are two ways of magnetization: direct magnetization and indirect magnetization. Direct magnetization is to place the material to be inspected directly in a strong magnetic field to magnetize it as a whole; indirect magnetization is to place an electromagnetic coil or a magnetic yoke around the material to be inspected to generate a magnetic field, so that the material to be inspected is partially magnetized.
3. Coating magnetic powder: Coat the magnetic powder evenly on the surface of the material to be inspected. Magnetic powder usually uses ferromagnetic powder, such as ferrite. There are two methods for coating magnetic powder: dry method and wet method. The dry method is to sprinkle the magnetic powder directly on the surface of the material to be inspected, and then apply it evenly with a brush or spray gun; the wet method is to dissolve the magnetic powder in a solvent and apply it on the surface of the material to be inspected by spraying or dipping.
4. Observation and analysis: After coating the magnetic powder, the defects on the surface of the material to be inspected will absorb the magnetic powder, forming visible magnetic powder traces. The location, shape and size of the defects can be observed by naked eye observation or with the help of magnifying glasses, microscopes and other tools. According to the characteristics of the magnetic powder traces, the nature and severity of the defects can be judged.
5. Result evaluation: According to the results of observation and analysis, the quality and safety of the inspected material are evaluated. If the defects are found to exceed the specified standards, corresponding repair measures or scrapping are required.
