The Magnetic Flux Leakage Testing System Design And Its Application For Finished Oil Pipes And Casing

As the special purpose pipe, oil pipe and casing are necessary part in the oil and gas exploitation. Casing is one-off used pipe that fixed on the inside wall of drilling well with cement to isolate oil gas and water layer, and to reinforce the oil layer and the wall of well. It has been effected by liquid eroding, oil layer pressure changing, external force changing while repairing the well, and some other factors. It couldn't be repaired while broken and so is very important to be detected before put use into the well.In this article, we analysed the testing method and the equipment of the special purpose pipe of nation and overseas, based on magnetic flux leakage theory and the fact that there are collar and screw thread on oil pipe and casing, we study the high precise magnetic flux leakage utility method to detect the multi-specification oil pipe and casing to meet the need of nation. In this method, horizontal and vertical magnetize outfit and detecting probe are fixed, the pipe made a spiral mode moving driven by polyurethane roll-type wheel, and realized the horizontal flaw and the vertical flaw signal combined collecting, detecting and analyzing. In the control system, with PLC, it realized the automatic running, which include pipe charging, forging ahead, magnetizing, detecting, demagnetizing, mark punching, baiting and signal collecting, data saving and so on.with laboratory and field experiment, we made optimize design in some aspect. in the transmission system, the appropriate wheel material, driven outfit and layout mode has been considered. And the all multi-specification pipe driven stable and smooth with least dynamic force. Comparing several magnetizing method, we choose the high efficiency and low heating one that won't hold the pipe. And also a stability detecting probe construction has been obtained after design and improve the induction coil link mode for several times,Based on comprehensive designing and improving, we developed an automatic magnetic flux testing system which suitable for multi-specification oil pipe and casing. The system has detected 20,000 meters pipes, statistic shows that the system has a benefit of high stability, easy to operate and maintain, convenience to change the probe and adjust the pipe's specification. The miss probability and the misdeclaration rate are lower than 1%, the remnant magnetism is lower than 5 Gauss, which can satisfy the API criteria. And the reliability and dependability of oil pipe and casing are increased.