Over recent years there has been an increasing interest in the initial testing and in-service inspection of many engineering products, particularly in relation to items such as aircraft, oilrigs, pressure vessels and pipelines. (Thompson 1976, Lumb 1977) For this purpose a wide range of nondestructive testing techniques has been developed, for both defect location and sizing. these have included the use of X-rays, electromagnetic induction and dye penetration, with the addition, in recent years, of the increasingly important methods which use ultrasonic waves. There is a wide range of methods of ultrasonic testing which use the different types of elastic waves and display the resulting information in a variety of ways.