A Multiple-Echo Calibration Technique for Guided Wave Testing

Abstract

Guided wave testing has become an established technology for screening long lengths of pipe for safety-critical defects from a single transducer position. The location of any defect is accurately determined and a rough idea of defect severity is obtained. However, it would be very beneficial to obtain a more accurate severity estimate from the guided wave data, especially in cases where follow-up inspection is expensive. This requires a more reliable calibration technique than the conventional approach, which relies on assumptions about the amplitudes of weld reflections. A multiple-echo calibration technique using data collected with standard test protocols but processed to extract the amplitude of reverberations between two features on either side of the sensor ring is presented, which removes the need for assumptions about the weld reflection amplitudes that reduce the accuracy of the conventional method of calibration. This novel technique is less dependent on operator judgement, and field examples presented show that it gives more accurate measures of cross-section loss than the conventional calibration technique. The improvement is particularly marked in cases where the weld geometry is not known or is nonuniform.