Advances in defect characterisation using long-range ultrasonic testing of pipes

Ultrasonic guided waves have been used for the rapid screening of pipes and pipelines for corrosion over the past 10 years. The hardware used in guided wave testing has improved since the early equipment, and now has up to 24 transmit-receive channels. This added capability has facilitated step changes in the way these tests are conducted, and has led to the introduction of better phased array focusing of guided waves and greatly enhanced postprocessing techniques. The focusing technique provides increased sensitivity to defects and information about their circumferential position and extent. However, it relies on defects being detected in the initial screening test to identify the locations at which to apply the focused excitation. This paper presents an enhanced signal display technique that presents the operator with more information from the initial screening test, helping to prevent false negatives and to choose effective focal positions. A defect characterisation method is then presented that convolves information from this focused inspection with the information from the initial screening test to give defects a severity rating. Defect severity and position can be assessed with a higher degree of confidence than was previously, achievable. The process has been tested under field conditions and has been shown to give good results.