Guided wave testing performance studies: comparison with ultrasonic and magnetic flux leakage pigs

Guided wave testing (GWT) of pipelines has been deployed commercially for more than a decade and has now become established, particularly in the oil industry. Standards for its use are emerging and it is widely accepted to be a method of NDT in its own right. This paper presents the findings of a practical in-situ study of the deployment of GWT. Its performance is compared, on two example pipelines, to that of established inspection using ultrasound (UT) and magnetic flux leakage (MFL) pigs. The significance of the comparison is that pigging and GWT are the two available options for 100% volume coverage of the material of a pipe and their roles are strongly complementary. In the first example, the GWT measurements were able to identify all of the indications that had been found by the UT pig. In the second example, in which the pipe was in a very poor condition, both the GWT and the MFL pig correctly found the extensive generalised corrosion, but did not correspond well in their calls for specific indications. Moreover, in each case reported here, the GWT additionally identified a relevant indication that was not found by the pig and which was subsequently confirmed in location and severity by UT thickness gauging. Overall, the conclusion of the study is that the GWT detection of indications in these examples compares very well with the results obtained from the UT and MFL pigs.