Research On Key Technologies Of Magnetic Non-destructive Testing For Smooth And Straight Pipe

Pipes must be detected non-destructively according to correlative standards in the factory to ensure that the internal and external surfaces have no minor defects, such as the existence of cracks and holes, at the same time wall thickness changes can be guaranteed in the range of permit. So it is very important to make a research on the testing method for the defects and wall thickness of pipes. So the research of steel pipe's rapid automation non-destructive testing is very important and the testing equipment is urgently needed.According to the requirement of automatic testing system at high speed and the analysis of local small flaws and holes of pipe, taking into account the manufacturing capacity and cost, swing-type probe inspection methods based on electromagnetic magnetization and rotary-type probe inspection methods based on permanent magnetization were studied, and magnetic flux leakage testing method for steel pipe vertical cracks was achieved. Through experiments, the characteristics of these two methods were compared and the rotary-type probe inspection methods based on permanent magnetization, way of signals collection and the structural designing were researched. Based on these researches, a kind of rotating testing system of multi-pole magnetizing with permanent magnet is presented in this article .Being utilized in qualitative supervising of oil pipe, the system has been used to help the pipes'manufactures test their products efficiently.Wall thickness must be measured as the API improved the testing standards for pipe quality. Consequently a method employing the magnetic flux leakage magnetic and a bridge-based method is researched to measure the wall thickness of pipes. After comparisons of the characteristics of each method,the bridge-based method is researched as a emphases. A wall thickness measurement equipment is designed, and its capability has been tested. The full pipe wall thickness measurement system is designed based on these researches .Up to now, the system has been proved to be fast and credible.