The Study on Defects of 6-Inch Cylinder by Electro Magnetic Acoustic Transducer (EMAT)

There are sets of considerable numbers of pipes in the oil refining, petrochemical and other plants. The pipes are mostly used with metal as conduction pipes, using solder joints to form a piping system. The metal pipes demand for a layer of insulation coated in the pipe surface to achieve the purpose of insulation and corrosion, because of long-term transport of gas and liquid. Due to the space limits, the pipes are bent into a variety of angels or buried under the ground surface. Because the coated pipelines are not easy to disassemble and are buried under the ground surface, it is hard to observe the flaw of the pipelines. Once the pipeline defects occur, there will be an extreme threat for the industrial safety, causing significant loss of plant operating and personnel safety. As the non-destructive testing (NDT) technology was developed fast, the fast and long-range ultrasonic testing technique is often used for pipeline inspection. Electromagnetic acoustic transducer (EMAT) is non-contact, without coupling operation, and suitable for testing at high temperature or defects at rough pipeline surface. This study aimed to detect the artificial pipeline by using EMAT, and to explore the relation between the defect and signal. By measuring the signal amplitude, we discovered that the length of the defect increases with the amplitude attenuation and the depth of defect will affect the amplitude attenuation. In addition, the amplitude attenuation will increase with flat-bottomed hole area of the defect obviously. This study showed that the signal amplitude attenuation of EMAT can be affected by the defect depth, the defect length, and the hole area of the pipeline.