I was recently fortunate enough to witness an impressive guided wave testing (GWT) demonstration where verification of a previous inspection result was required. The organisation that was responsible for the inspection was not aware that we were going to carry out a re-inspection of the pipe section and the available equipment was different to that which was originally used. The original inspection used a Wavemaker G3 and the re-inspection was performed with a Wavemaker G4 and a different transducer ring.

Equipment set-up and data collection took a very short period of time, just a few minutes per test location. The result from the verification test was overlaid on the original data trace and, after a slight adjustment to accommodate the different position of the transducer ring, a direct comparison could be made. What was very impressive was the similarity between the initial results and the retests; there were minimal differences. Two further pipes were tested and the traces were overlaid on the previous results and, again, the repeatability was very impressive. This is from a method that can test 1 km of insulated pipe in a day without removing all of the insulation or taking it out of service.

The method does have some limitations, but there are many practical applications where it can offer significant advantages. One such example is for the monitoring of pipe condition using a permanently-installed transducer ring. This allows repeat measurements of inaccessible pipe sections to be taken ‘at will’. Overlaying the results gives a precise measurement of pipe degradation.

John Moody, BINDT
http://www.bindt.org