| Mechanical damage is one of the predominant causes of pipeline incidents. In-line inspection of mechanical damage in pipeline is of great importance. Different from corrosion, mechanical damage refers to dents and gouges caused by impingement on the outside of the pipe, e.g., from a backhoe tooth striking the pipe during digging operations. Characterization of mechanical damage to determine potential for pipeline failure requires that stresses and plastic deformation be determined;it is not sufficient to measure only the geometry of the defect. Now, there are mainly two potential method under research in overseas, magnetic flux leakage (MFL) method and nonlinear harmonics (NLH) method. As to the MFL method, the funding is large, the system structure is big and the data process method is complex. This paper is engaged in research on the NLH method, especially on the inspection mechanism and sensor circuit design.Nonlinear harmonics inspection method is based on the fundamental principle of magnetoelastic effect and electromagnetic induction. In the paper, the fundamental principle of NLH method is introduced, and a kind of mechanical damage inspection sensor based on FPGA is designed;especially the design of the sensor, the signal generator and the circuit for synchronous detection is explained in detail. Meanwhile, a data collection circuit is designed and some different artificial defects are made on a plate with the same material as the pipe. Two kinds of mechanical damage defects such as gouges and dents were detected in the experiment.With the two kinds of typical mechanical damage were tested and analyzed. The experiments results show that NLH sensor can detect and characterize mechanical damage such as gouges or dents effectively and the approach to be taken in this project appears feasible. Furthermore, the NLH sensor can be miniature, low-noise and low power consumption, and which can be suitable for in-line inspection for mechanical damage in pipelines. |
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