Pulsed Eddy Current Testing In Ferromagnetic Pipeline Corrosion With Cladding Layer Under Complex Conditions

With cladding layer ferromagnetic pipeline has been widely used, when be used for a long time, interior and exterior walls of ferromagnetic pipeline corrosion occurs.It can be taken a quick scan using pulsed eddy current detection technology without dismantling cladding layer, efficiently completing the detection of coated layer ferromagnetic pipeline in service.In the lab for testing, it is a good test environment without any other ferromagnetic pipelines around the test tube.But in the actual detection, there will exist a lot of interferences to be detected, and installation error of the artificial operation or layer caused by inaccurate test results.Therefore, it is very necessary to solve all these problems.This paper analysed the influence of position difference,which are from two aspects of the finite element simulation and experiment of interference.Analysed by ANSYS software,the simulation result shows that it will be an affection to the detection if there is interference around the tested pipe 0.6 m,making the induction voltage decays slowly.By experimental verification, the results are consistent with the simulation.Analysing the influence on detection of three conditions: parallel interference tube,T interfere pipe and cross interference.Analysing the interference from three aspects of the induced voltage in section of decay curve, and the sensitivity respectively.When testing on the surface of the parallel tube,it will not affect the detection.When detecting the surface of parallel tube, as long as the two pipe spacing is less than 0.6 m, the attenuation of induced voltage will change slowly and the detection will be more sensitive.When the vertical distance of T-tube and detector tube is greater than 0.5m, it will not affect detection.Cross tube can change sectional view of the test results and the trend of affected part will be rising or falling.According to these interference factors,two kinds of the methods has been put forward to solve these problems: increasing magnetic shielding cover and using U probe.Testing in the two cases of parallel interference pipe and cross interference respectively,the feasibilities of two methods have all been verified.The experimental results show that the increase of magnetic shield can only improve the induction voltage values and did not reach the expected goal.U probe has strong anti-jamming capability and inhibit the change of the section.The different thickness of the coating layer and human improper operation will cause the inaccurate test results,lift-off error and even detection mistakes.This paper put forward a method which can distinguish the difference of lift-off,defect and difference between defect and lift-off techniques, according to experiment verification.After verification experiment,this method can be well applied to distinguish outer wall defects,lift-off and defect on the outer wall defect.But for internal defects,it can only distinguish separate defect point,however the distinguish between lift off and defect on the outer wall defect is not obvious.