Development of a synthetic A-scan technique for ultrasonic testing of pipelines

Multiple boundary echoes are often seen in ultrasonic testing of materials. Although these echoes can be a problem in many situations, they can also be used to advantage e.g. in identifying disbonds of laminates or properties of materials beneath the test surface, such as scale deposits in pipelines. However, that requires echo comparison with signals from reference acoustic targets or templates. This is an exhaustive process, particularly when testing non-planar materials such as pipelines. In this paper, a new approach to synthesise reference signals using numerical modelling and computation is presented as an alternative method. The results of signal synthesis have been verified by experiment. Although the techniques described are specifically related to testing of pipelines, they can be extended to other general applications in nondestructive testing of materials.