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

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 double-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.