Improvements to the performance of guided wave testing on coated and buried pipes

Mudge, Peter; TWI Ltd; United Kingdom

Mudge, P.; Plant Integrity Ltd; United Kingdom
Deere, M.; Plant Integrity Ltd; United Kingdom
Pedram, K.; Plant Integrity Ltd; United Kingdom
Duan, W.; Brunel University London; United Kingdom

ID: ECNDT-0527-2018
Download: PDF
Session: Guided Waves techniques 2
Room: G3
Date: 2018-06-14
Time: 15:40 - 16:00

Ultrasonic guided wave testing has become an established method for testing long lengths of pipes economically from a limited number of test locations. Conveniently, regions that are hard to access, such as spans over roads or rivers, in culverts or where pipes enter the ground, may be inspected from adjacent positions which may be reached more easily. However, where pipes are buried or are in other areas where corrosion may be severe the pipe, which is usually ferritic steel, is normally protected by a barrier coating on the outside. These coatings are usually visco-elastic in nature. The mechanical properties are such that they readily absorb elastic ultrasonic vibrations, so that the attenuation rates for guided waves transmitted along the pipe are considerably higher than for bare pipe. This increased rate of signal loss significantly reduces them usable test range. In addition, the background noise on the signals tends to be greater than for bare pipe, thereby reducing sensitivity to defects, so that the use of guided wave testing becomes less attractive as an inspection option. An extensive programme of work has been carried out by TWI, Plant Integrity Ltd and Brunel University Innovation Centre to address this issue. A combination of model-led procedural enhancements, improved instrumentation functions and novel signal post-processing has been shown to achieve considerable improvements to both test range and sensitivity to defects in coated and buried pipes. Results are presented for a variety of cases to demonstrate the improvement in performance achieved.