为了解决传统轴向导波对管道斜向裂纹检测灵敏度低的缺点,基于电磁超声螺旋导波检测机理,提出了一种适用于管道斜向裂纹检测的S构型内检式EMAT(电磁超声换能器)。针对所提换能器,建立金属管道电磁超声螺旋导波检测有限元模型,探究不同螺旋角螺旋导波在管道上的传播过程和回波信号特征。搭建了电磁超声螺旋导波检测试验系统,采用所提EMAT和L(0,2)轴向导波EMAT对斜向裂纹进行检测。试验结果表明,S构型内检式EMAT对于斜向裂纹具有更高的检测灵敏度,对于裂纹的高分辨率检测具有重要意义。

In order to mitigate the pitfall regarding low sensitivity of traditional axial guided waves to oblique cracks in pipes, based on the mechanism of electromagnetic helical guided ultrasonic wave evaluation, an inner-inspection Electromagnetic Acoustic Transducer (EMAT) in S configuration was proposed. In regard to the proposed transducer, a finite element model was established to explore the propagation process and echo signal characteristics of helical guided waves with different helical angles on the pipes, and its response to cracks in different orientations. In parallel, an electromagnetic ultrasonic helical guided wave testing system was built up. The proposed EMAT was fabricated and adopted for detection of oblique-angled cracks. Results from simulations and experiments indicated that the proposed inner-inspection EMAT in S configuration had higher evaluation sensitivity to oblique cracks, implying the significance for high-resolution evaluation of cracks in metallic pipes.