The feasibility of using torsional guided wave for corrosion detection in buried steel gas pipes (with a diameter less than 5 cm)

Abstract

Corrosion is one of the major issues for a wide range of industries, hence effective, rapid and low cost methods of pipeline inspection are needed. Compared with existing methods, the ultrasonic guided wave method has been found as an attractive alternative for the inspection of pipelines. However, there is a clear need to support different pipe sizes in a long range without excavation. In this project, small pipes (with a diameter less than 5 cm) are considered due to a request by Scotia Gas Network Ltd. The aim of the work presented here is to investigate the feasibility of torsional guided waves for inspecting buried pipes with a small diameter. In order to understand wave propagation, the wave displacement on plates and pipes (described theoretically) is used to generate MATLAB scripts. These scripts find the phase and group velocity dispersion curves for plates and pipes of varying size and thickness. The pipe is considered to be lossless, and the effect of attenuation was ignored in the calculations for this project. Upon finding the theoretical guided wave characteristics, real world analyses were conducted to see if the aim could be achieved in an experimental scenario. Experimental questions addressed in this report include: “How can the transducers be clamped to the plate and to the pipe?”; “What is the best propagation frequency?”; and “How can the wave velocities and appropriate transducer positions be found?”. Once these were answered, work on pipes with artificial defects could begin. A steel pipe with a diameter of 3.4 cm and wall thickness of 0.55 cm with three different defect sizes was examined. A defect with 8.3% Cross Section Area (CSA) was found by generating a torsional mode T(0,1) at 50 kHz on the pipe. Smaller defects were not found due to high reverberation levels in high frequency propagation. This was due to having only a limited number of transducers. Further work using more transducers and an experimental setup with a buried pipe (to include attenuation) is recommended.

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ORCID for Victor Humphrey: orcid.org/0000-0002-3580-5373

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