Guided waves for power plant applications

Abstract

This study explores the possibility of using the guided wave non-destructive testing technique for power plant applications. Guided waves are already used extensively in the petrochemical industry, however the nature of pipework in a power station has meant that guided waves have not been studied for use in this environment. Power station pipework is more challenging to inspect than petrochemical pipework using guided waves because the pipelines tend to be shorter, and the feature density is much higher, with welds, hangers, supports and bends all contributing to make analysis of results more difficult. A particular focus of the study was detecting axially aligned defects in pipes, a problem that emerged in the UK coal power station fleet in 2006. Guided waves provided a desirable inspection technique because large volumes of pipework can be screened quickly, this being particularly advantageous due to the high volume of pipework that requires inspection. Two guided wave approaches to detecting axial cracks in pipes were pursued. Long- range guided waves were initially examined as they are able to examine large quantities of pipework in a short amount of time. Unfortunately, long-range guided waves are sensitive to the change in cross-sectional-area of a pipe, and axially aligned defects produce only a very small change in cross-section. Therefore long-range guided waves were not sensitive enough to detect a critically sized axial crack. The sensitivity of long- range guided waves was improved using a synthetic focusing algorithm, although this was still insufficient to detect a critically sized defect. The second guided wave approach was to utilise circumferential guided waves to detect axial cracks in pipes. Although many of the advantages of long-range guided waves are lost, using circumferential guided waves is much faster than an alternative manual ultrasonic inspection. The results of circumferential guided wave experiments suggest that they would be capable of detecting a critically sized axial crack in a pipe. Besides attempting to detect axial cracks guided waves have been tested on a small number of other power station pipework systems. These systems were tested as a way to examine the viability of using guided waves as a general inspection tool at a power station. Although guided waves are not suitable for every application, there are a good number of potential applications due to the wide variety of pipework systems at a power station.