脉冲远场涡流检测双层钢管横向裂缝仿真研究

Simulation of Transverse Crack Detection in Double-layered Steel Tube Using Pulsed Remote Field Eddy Current Method

油套管和海底输运管等双层结构钢管,其横向裂缝是可能导致管道断裂的危害性缺陷。对脉冲远场涡流检测双层结构钢管的横向裂缝进行了有限元仿真研究。给出了内外完好、内裂外好、内好外裂、内裂外裂情况下的管道磁场分布、接收线圈上的感应电压衰减曲线、检测时间剖面图及检测灵敏度曲线。仿真结果显示脉冲远场涡流方法对内管和外管的横向裂缝均可进行有效检测;管道裂缝的存在导致其磁场分布与完好管道不同,从而在接收线圈上引起感应电压下降曲线的不同;内管裂缝在接收电压信号的早期出现明显的缺陷显示,外管裂缝的缺陷信号则在接收电压信号的后期才更明显。内管裂缝出现时接收线圈感应电压高于无缺陷时,而外管裂缝出现时接收线圈感应电压低于无缺陷时。在内管存在裂缝时,用此方法判断外管同一位置是否也有裂缝较困难。

Transverse cracks are dangerous for double-layered steel tube in such as oil casing string and undersea pipe-in-pipe systems. Transverse crack detection in doub｜e-layered steel tube using pulsed remote field eddy current method is studied using finite element simulations. Distributions of the magnetic field in the inspection for undamaged inner tube with undamaged outer tube, cracked inner tube with undamaged outer tube, undamaged inner tube with cracked outer tube, and cracked inner tube with cracked outer tube are given in the simulations as well as voltage decay curves of the receiving coil, time slices of voltage and sensitivity-time curves. Simulation results show that the pulsed remote field eddy current method can detect transverse cracks both in inner and outer tube effectively. Distribution of the magnetic field and then voltage decay of the receiving coil are different when a crack exists in double-layered steel tube. The obvious defect signals of cracked inner tube appear in the early time of received voltage signal and the defect signals of cracked outer tube appear in the late time of received voltage signal. Voltage in the receiving coil is higher when cracked inner tube combined with undamaged outer tube and lower when undamaged inner tube combined with cracked outer tube than undamaged inner tube combined with undamaged outer tube. It is difficult to inspect cracks in the outer tube when a crack appears in the inner tube at the same location, for the defect signals of cracked outer tube are shielded by those from the inner tube crack.