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首页> 美国卫生研究院文献>Sensors (Basel Switzerland) >Eddy Current Testing with Giant Magnetoresistance (GMR) Sensors and a Pipe-Encircling Excitation for Evaluation of Corrosion under Insulation
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Eddy Current Testing with Giant Magnetoresistance (GMR) Sensors and a Pipe-Encircling Excitation for Evaluation of Corrosion under Insulation

机译：使用巨磁阻（GMR）传感器和管道环绕励磁进行涡流测试以评估绝缘下的腐蚀

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This work investigates an eddy current-based non-destructive testing (NDT) method to characterize corrosion of pipes under thermal insulation, one of the leading failure mechanisms for insulated pipe infrastructure. Artificial defects were machined into the pipe surface to simulate the effect of corrosion wall loss. We show that by using a giant magnetoresistance (GMR) sensor array and a high current (300 A), single sinusoidal low frequency (5–200 Hz) pipe-encircling excitation scheme it is possible to quantify wall loss defects without removing the insulation or weather shield. An analysis of the magnetic field distribution and induced currents was undertaken using the finite element method (FEM) and analytical calculations. Simple algorithms to remove spurious measured field variations not associated with defects were developed and applied. The influence of an aluminium weather shield with discontinuities and dents was ascertained and found to be small for excitation frequency values below 40 Hz. The signal dependence on the defect dimensions was analysed in detail. The excitation frequency at which the maximum field amplitude change occurred increased linearly with the depth of the defect by about 3 Hz/mm defect depth. The change in magnetic field amplitude due to defects for sensors aligned in the azimuthal and radial directions were measured and found to be linearly dependent on the defect volume between 4400–30,800 mm3 with 1.2 × 10−3−1.6 × 10−3 µT/mm3. The results show that our approach is well suited for measuring wall loss defects similar to the defects from corrosion under insulation.
机译：这项工作研究了一种基于涡流的无损检测（NDT）方法，以表征隔热下管道的腐蚀，隔热是隔热管道基础设施的主要失效机制之一。将人工缺陷加工到管道表面，以模拟腐蚀壁面损失的影响。我们表明，通过使用巨磁阻（GMR）传感器阵列和大电流（300 A），单正弦低频（5-20​​0 Hz）管道环绕激励方案，可以量化壁损耗缺陷而无需去除绝缘层或防风雨罩。使用有限元方法（FEM）和分析计算对磁场分布和感应电流进行了分析。开发并应用了消除与缺陷无关的杂散测量场变化的简单算法。确定了铝制防风雨罩的不连续性和凹痕的影响，发现对于40 Hz以下的激励频率值影响很小。详细分析了信号对缺陷尺寸的依赖性。出现最大场振幅变化的激励频率随缺陷深度线性增加约3 Hz / mm缺陷深度。测量了由于缺陷导致的沿方位角和径向方向对齐的传感器产生的磁场振幅变化，并线性地取决于缺陷体积在4400–30,800 mm 3 与1.2×10 之间−3 −1.6×10 −3 µT / mm 3 。结果表明，我们的方法非常适合于测量与绝缘层腐蚀引起的缺陷相似的壁损缺陷。

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