TWI Industrial Member Report Summary 227/1983
By P M Bartle
A new condition monitoring technique for use on large structures is being developed at The Welding Institute. It is based upon the fact that if a constant acoustic/ultrasonic signal is injected into one point on a structure and is detected elsewhere in the structure, then the received waveform remains constant as long as the network of acoustic paths between the input and receiving points remain constant. If a defect grows in the acoustic network, then the waveform of the received signal changes. Such changes can be used to detect defect growth and initially at least, the prime function intended for the technique is that of a monitor for large (say >20mm) defect growths on very large structures such as oil rigs. The tests have also shown that some location and sizing capability exists, although at present, it is not clear how far these, and sensitivity that was found to be much higher than expected, can be utilised in practical situations. The system is capable of working with intertransducer distances of tens of metres, and while sensitivity is likely to depend upon transducer separation, defects of a few millimetres in dimensions have been detected. The report reviews the technique as currently understood, compares it with competing techniques and outlines the ad hoc experiments carried out to date.