用于镀锌铁皮保护层下检测的脉冲涡流技术研究

Research and application of pulse eddy current testing technology with galvanized steel cladding

在实际应用中,脉冲涡流检测技术会受到保温层外的保护层的影响,其中镀锌铁皮保护层对脉冲涡流信号影响较大。研究了不同保护层对脉冲涡流信号的影响,重点分析了镀锌铁皮厚度、提离高度和镀锌铁皮振动对脉冲涡流信号的影响,并提出了解决方案:当提离高度相同时,带镀锌铁皮保护层的脉冲涡流信号幅值较不带保护层时的信号幅值大幅减小,此时需选择穿透能力更强的检测探头并提高发射电流强度;当以晚期信号斜率作为表征壁厚的特征值时,提离高度对计算壁厚的影响较小;考虑到磁致伸缩引起的探头振动,检测过程中应避免检测探头与镀锌铁皮直接接触。

In practical applications,pulse eddy current testing technology is affected by outer protective layer of the insulation layer,among which the galvanized steel cladding has a significant impact on the signal.The influence of different protective layers on the pulse eddy current signal was studied,especially the effects of thickness,lift-off and vibration of galvanized iron sheet on the signal;meanwhile,the solutions were put forward.When lift-off was the same,the amplitude of the pulse eddy current signal with galvanized steel cladding was dramatically reduced compared to the signal without cladding.In this case,the detection probe with stronger penetrating ability should be selected and the transmitting current intensity should be increased;when the late signal slope was used as the characteristic value of wall thickness,lift-off has little influence on the calculation of wall thickness.Considering the probe vibration caused by magnetostriction,direct contact between the probe and galvanized steel cladding should be avoided during the detection process.