钢管内壁缺陷涡流检测的机理研究

Study on Mechanism of Eddy Current Testing for Inner Defect of Steel Pipe

钢管涡流检测多采用磁饱和技术以抑制磁导率波动引起的信号噪声,检测实践中发现此时内壁缺陷被检出,这与趋肤效应原理相矛盾。建立了含内壁刻槽的钢管磁饱和下的仿真和试验模型,剖析了内壁缺陷检出机理。仿真和试验结果表明:钢管缺陷漏磁场在探头内引起低频响应经相敏检波后被滤除,对信号无作用贡献,内壁缺陷在钢管外壁引起的磁导率畸变是影响信号的真正根源。研究结果明确了磁饱和下钢管涡流检测机理,可望指导钢管的工程实践检测。

The magnetic saturation technology is widely applied to eddy current testing （ECT） of steel pipe to suppress signal noise caused by magnetic permeability fluctuating. It is contradictory to the skin effect principle when inner defects of steel pipe are detected during inspection. The ECT simulation and experiment model of steel pipe eontained inner groove are developed. The detection mechanism of inner defects is analyzed in this paper. The simulation and the experimental results show that the low frequency signal caused by the leakage field of steel pipe is filtered by phase sensitive deteetion and is not contributive to the impedance signal. The real reason of affecting signal is the distortion of outer wall permeability which is caused by inner defects of steel pipe. The results show the ECT mechanism of steel pipe using magnetic saturation and provide some valuable references for nondestructive testing practice.