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将两端短路的金属管道内部视为谐振腔,管道壁减薄导致了腔体体积的变化,据此,可以利用谐振频率的偏移进行管道壁减薄的评价。基于谐振腔微扰理论,构建管道壁减薄的测量系统,采用单个同轴电缆实现管道内部微波的发射与接收,使用TM_(01)模式电磁波以实现管道壁减薄的检测工作。针对上述过程,建立了检测系统的有限元模型,进行了减薄程度的参数化扫频计算,并搭建了相应的扫频测量系统,扫频获得了不同减薄程度下的谐振频率。对比有限元计算结果和测量数据可知:二者具有较高的吻合程度,且谐振频率的偏移随着管道壁减薄尺寸的增加而增大。因此,谐振腔微扰法可用于管道壁减薄的评估,是在役管道的一种有效无损检测方法。
Considering the inside of the metal pipe with short circuit at both ends as the resonant cavity, the thinning of the pipe wall leads to the change of the cavity volume. Therefore, the thinning of the pipe wall can be evaluated by the shift of the resonant frequency. Based on the theory of cavity perturbation, a measurement system of pipe wall thinning was constructed. A single coaxial cable was used to transmit and receive the microwave inside the pipe. TM_ (01) mode electromagnetic wave was used to detect the pipe wall thinning. Aiming at the above process, the finite element model of the detection system is established, the parametric sweep calculation of the thinning degree is carried out, and the corresponding swept frequency measurement system is set up. The resonant frequency under different thinning levels is obtained by sweeping. Comparing the finite element calculation results with the measured data, we can see: the two have a high degree of agreement, and the shift of the resonance frequency increases with the increase of pipe wall thinning size. Therefore, the cavity perturbation method can be used to evaluate the thinning of pipe wall, which is an effective non-destructive testing method for in-service pipelines.