Abstract: The technique is based on comparing the spectral response of the "suspect" signal with that of a reference signal. The "suspect" signal is a signal detected in the weld heat-affected zone by a high-frequency (10 MHz), angle-beam (typically 45 degree) shear wave transducer operated in the pulse-echo mode. The reference signal is taken from the base metal next to the weld or heat-affected zone with two matched transducers of the same kind as the pulse-echo transducer but operated in the pitch-catch mode. The two signals are gated and Fast Fourier Transformed to the frequency domain for comparison. Relative to the reference spectrum, the high temperature hydrogen attack spectrum has an amplitude which increases with an increase of frequency, while welding defects and inclusions have the same frequency dependence as the reference spectrum. Therefore, localized high temperature hydrogen attack can be easily differentiated from other defects due to its unique spectral response.

Abstract: This invention is a new inspection technique using ultrasonic Lamb waves to measure reduction of pipe wall thickness due to localized corrosion at pipe supports. The technique uses two transducers in a pitch-catch mode to send and receive a selected Lamb wave. The wave travels along the pipe wall in the circumferential direction. The reduction of the pipe wall thickness at the pipe support changes the time-of-flight between the two transducers. By comparing time-of-flight data measured from the pipe support area and from areas adjacent to the pipe support, one can quantify the change of time-of-flight due to the pipe corrosion wall loss at the support. A mathematical model, a sizing algorithm and a PC program have been developed to quantitatively relate in time-of-flight to the minimum remaining wall thickness. With them, one can quantify the minimum remaining pipe wall thickness at a pipe support by simply measuring the change in the time-of-flight.