Magnetic generation and electrostatic detection of pressure pulses in a steel pipe
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The investigation of a non-intrusive method to detect defects in metal pipelines has been started. A generator produces a pressure pulse, which travels along the pipeline. A detector monitors the reflected signals from discontinuities such as thin spots or fractures in the pipeline. Both the generator and the detector are external to the pipeline and do not have to be in mechanical contact with the pipe. The generator consists of a coil enclosing the pipe. The coil is excited with a short high-current pulse. The magnetic pulse generated by the current pulse compresses the pipeline sending pressure pulses up and down the pipeline. The detector consists of an insulated cylindrical electrode around the pipe. When a reflected pulse from some discontinuity along the pipeline returns to the detector it causes a temporary local change of the pipe diameter due to the coupling of the longitudinal and the azimuthal strain of the material. This change in diameter causes a voltage change of the charged electrode, which is amplified and analyzed. The location of the defect can be inferred from the delay of the reflected signal. Measurements with mechanical and magnetical excitation of pressure pulses have been performed. Reflections from the ends of the pipe are clearly detected.