Research And Applications Of Metal Magnetic Memory Testing Method On Special Equipments

With economic rapid development, more and more Special Equipments are increasingly applied in the industrial production. Special Equipment, as we call, is referred as the equipment or device that is characterized by Life safety involved high risk ,such as Boilers, pressure containers(containing a spirit bottle), pressure piping,elevators, derrick devices, passenger transportation cableways and large-scale amusement devices. It is inevitable for these equipment to produce stress concentration to a certain degree because of complexity of structure, variety of parameters, remaining forces in wedging manufacture process and the circumstances of high temperature, high pressure and corrosion. Stress concentration is a major factor giving rise to equipment fragmentation,fatigue failure and stress corrosion. Therefore it has great realistic significance on keeping the occurrence of disaster and accident to seek out the stress concentration position and conform the stress concentration's magnitude,and make early-stage flaw diagnosis for stress concentration.Currently, normal non-destructive testing methods(MT, PT ,UT, RT) is very difficult to effectively detect the stress concentration zone. However, metal magnetic memory testing method can quickly and accurately find out the stress concentration part existed in the equipments. Metal magnetic technology development time is very short and there have been many problems when metal magnetic technology is applied in the practice. In the paper, the specific application study of MMM technology were carried on from the analog experiments in lab to practical application in field. The research contents are as follows:(1) In Lab, the loading test was held on crane girder with jointing crack; magnetic memory examination was carried on test plank with various?macroscopic?flaws. The relation of the MMM signal character of the flaw zone and the magnetic leakage field on the load was studied; the effect that metal magnetic memory examines macroscopic flaws was verified. The lab results show that without stress the range of magnetic memory signal increases with the gradual increment of the load; the macroscopic flaw signal scope of metal magnetic memory test covers the flaws of Ultrasonic and TOFD test. (2) Metal magnetic memory test was carried on crane track in field and 55 various pressure vessels in service ; Mmm signal characters on the crane track and pressure vessels were studied .It is concluded that magnetic memory signal characterized by symmetry in the crane tracks stems from small cars'wheels stopping on the tracks over a long period of time . The ratio of main amplitude variation range of MMM signal of the pressure vessel butt joints from 100 to 400 A/m is 16.8%.(3) A large amount of MMM signal characters of pressure vessels and other special equipments in field, were collected, classified, concluded and arranged. MMM signals fall into three main categories:Small signals, excrescent signals and macroscopic flaw signals.(4) MMM testing technology was used in the heat treatment assessment on the butt joints of the pressure vessels. The findings show that MMM method can effectively and perfectly assess the heat treatment effect.(5) MMM testing technology was tried to apply in the stainless steel, and a large amount of typical flaw MMM signals were gained. The findings show that mmm technology may be applied in stainless steel test.