A novel enhanced sensitive sensor for small-diameter pipe based on the PECT-EMAT hybrid testing method

Metal pipelines are widely used in oil, natural gas and other industries. Due to their long-term relatively harsh service conditions, various complex defects will inevitably occur both on the inner and outer wall. Conventional single non-destructive testing technology cannot detect both inner and outer wall defects simultaneously. A hybrid non-destructive testing technology combining pulsed eddy current testing and electromagnetic acoustic transducer (PECT-EMAT) is a good candidate to effectively solve this problem. However, the current research object based on this hybrid testing method is mainly for the flat plate or the large-diameter pipe similar to the flat plate. The increased curvature of small-diameter pipe will decrease the detection performance using traditional rigid sensing module due to the interface in-adaptation. Based on above background, this study proposes three different sensing configurations for curved pipe and their detection performance are investigated and compared. Firstly, the simulation model is built for the pipeline. Then, the near-surface eddy current fields excited by the planar and curved coils, the bias magnetic fields provided by the planar and curved magnets, and the Lorentz force excited by three types of sensors with different configurations are calculated and compared, respectively. Finally, the detection performance of the three different sensor configurations are compared through simulation and experiment. The results show that the designed novel composite sensor has the highest PECT sensitivity and the largest EMAT amplitude and SNR, which contribute to higher detection capability. To some extent, the proposed composite sensor can be employed to solve the problem of detection performance decreasing due to the increased curvature of smalldiameter pipe.