Magnetic particle inspection is a way to carry out ultrasonic inspection of pipe defects by using magnetic particle as display information material. According to the type of magnetized magnetic powder material, the inspection method is divided into wet method and dry method. According to the time of applying magnetic particles on the workpiece, the detection methods are divided into persistence method and remanence method.
1. Wet method and dry method
Magnetic powder floating in oil, water or other liquid material application is called wet method, it is in the whole process of inspection, the magnetic suspension is evenly distributed on the surface of the workpiece, the use of liquid fluidity and leakage of magnetic field to attract magnetic powder, show the appearance and size of the shortcomings of information. In wet test, because of the dispersing effect and floating characteristics of the magnetic suspension, the magnetic powder particles can be selected smaller. Therefore, it has a high test sensitivity. It is especially suitable for manufacturers of eddy current flaw detector to inspect subtle defects on the surface, such as fatigue cracks, cutting cracks, etc. Wet methods are often used in conjunction with mobile machinery and equipment, as well as with mobile and portable equipment. Magnetic suspension for wet process can be used in circulation system applications.
Dry powder method, in some unique places, can not choose the wet method to carry out the test, and the use of specially made dry magnetic powder strictly in accordance with the immediate application on the magnetized workpiece, workpiece shortcomings that show information magnetic marks. Dry inspection is mostly used for large and medium-sized castings, wool embryos of steel castings, large and medium-sized parts and parts, welding parts of the metal ultrasonic flaw detector inspection, generally with portable equipment mutual application.
2. Persistence method and remanence method
(1) continuous method continuous method is also known as the accessories magnetic field method or the current magnetic method, is in the addition of magnetic field effect, the magnetic particle or magnetic suspension is applied to the workpiece to carry out magnetic particle flaw detection. The observation and comment on the workpiece can be carried out in the effect of the external magnetic field, but also after the final magnetic field.
(2) Remaining magnetic method Remaining magnetic method is to first carry out the workpiece to be magnetized, and then pour the immersion suspension on the workpiece, and then carry out the observation after the magnetic particles gather. It is the method of using the remaining magnetic belt of raw materials to carry out inspection, so it is called the remanent magnetic method.