| Oil & gas pipelines are important energy source transmission facilities, online de-tecting of stress corrosion crack (SCC) of pipelines has large economic value. Remotefield eddy current (RFEC) inspection is one of newly developed technique which isused in tube nondestructive testing. It has the advantages that lifting-off and environ-ment have little effect on it and it is important for tube testing that RFEC inspectionhas same sensitivity for the internal and external defects in the tube wall. Thus, ithas proved a promising nondestructive inspection method for SCC. But the study ofmechanism of RFEC and its application on SCC detection is not advanced enough, sosimulation of RFEC using finite element software ANSYS, and mechanism of RFECand characteristic and factors of defects was researched.First, according to Maxwell equations, the axisymmetric and three dimensionalRFEC equation had been created, and the law about magnetic field spreading alongradial and signal in detection coil was got. Then 2D and 3D models of RFEC werecreated and optimized in ANSYS. In order to decrease the size of model,"Zoom-In"method was used, and so 3D simulation of SCC detection on PC became true. Afteranalysis on results from 2D simulation, estimation model of magnetic field distributionon the internal surface along axial was created, then magnetic field and electric fieldwere decoupled and the contributions of magnetic capacity and conductive capacity ofthe pipeline were found out. Signal of full circle defects as well as its characteristicand factors were analyzed in 2D model, then the fact that the peak value of phase isproportional to depth and the integral value of phase is proportional to width werefound out. In the end, block defects and SCC were simulated in 3D model, their signalcharacteristic and the relation between signal and width, length, depth factors were got.According the results in this thesis, detecting SCC in oil & gas pipelines is possible. |
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