The development and implementation of advanced ultrasonic phased array technology

Abstract

Ultrasonic inspection is the primary technique for the detection of planar flaws within the nuclear industry. Current inspections are typically limited to the application of rigid wedge, single element transducers to components with regular surface geometry. This thesis addresses some of the limitations of this approach and develops new methods and techniques that are suitable for application in an industrial environment. Inspection modelling is a cost effective technique for inspection design and qualification; it can be used to aid understanding of the inspection process, and provides valuable insight into inspection data interpretation. In this work semianalytical and numerical modelling tools have been used to accurately and efficiently simulate the ultrasonic inspection of large complex components. Modelling tools have also been applied to aid in the design of a membrane coupled conformable phased array device. The membrane coupled array is a low-cost, robust device that uses a conventional phased array coupled to the outer surface of the component under test via a water path encapsulated by low-loss membrane. Early design of this device was performed by Long and Cawley at Imperial College, London. The work reviewed in this thesis discussed the further development of this membrane coupled device and its application for the inspection of a specific target application component. The target application is a safety critical, thick-walled stainless steel section of pipework that contains an austenitic weld. The current inspection of this component is carried out by first removing the component weld cap and then mechanically raster scanning a large number of rigid wedge single element transducers. Weld cap removal is an expensive time consuming task that can lead to excessive wall thinning and the exposure of small surface breaking defects. The motivation for this work is to provide complete inspection of the weld and heat affected zone with the weld cap in place. It is also designed to improve inspection speed and accuracy, and to reduce the amount of user intervention required to complete the inspection in a hostile environment Inspection results from the 2nd and 3rd generation membrane coupled device on multiple test-pieces representative of the target application are presented. These results demonstrate that the membrane coupled device can be used to detect defects in locations that cannot be inspected using conventional techniques. The amount of scanning required can be significantly reduced, simplifying the inspection and helping to improve inspection speed by over 60% in comparison to the single element approach.