Investigating Crack Growth Monitoring using Guided Waves

Investigating Crack Growth Monitoring using Guided Waves

- London, 21 February 2017 -

Guided Waves is the special feature topic in this month's issue of Insight*, the official journal of the British Institute of Non-destructive Testing (BINDT).

Included in this special feature is the research paper "Crack growth monitoring using low-frequency guided waves"** which was co-authored by Chien A Chua, one of the PhD students sponsored by GUL at Imperial College.

We are proud to say that our latest gPIMS® corrosion monitoring system and advanced WaveProTM software was utilised in monitoring the growth of a defect in a weld under experimental conditions at the Pipeline Research Council International's facility in Houston, Texas.

Over the last decade, the level of interest in the use of permanently-installed monitoring systems to track the progress of damage has increased dramatically. Cracks in pressurised operational pipelines can lead to structural failure and could ultimately lead to a loss of structural integrity and, in some instances, endanger life. Guided wave testing (GWT) is a relatively new and advanced non-destructive method used to inspect pipelines. Using permanently-installed guided wave transducers and baseline comparison techniques, it has been possible to detect defects as small as 1% in pipe cross-sectional change (CSC) in operational piping. This paper investigates, through finite element (FE) modelling and experiments on steel pipes, the interaction of torsional guided waves with circumferentially-oriented cracks. The FE modelling results show that circumferential cracks at welds that have a larger circumferential extent and deeper profile will produce a bigger change in amplitude of the reflected torsional T(0,1) signal, since it will lead to a larger change in the cross-section of the pipe wall. The results indicate that higher inspection frequencies produce a larger reflection coefficient and can be approximated as a linear function of frequency for narrow cracks with a characteristic length-to-wavelength ratio of ≤4.7%. The FE model was validated experimentally on an 8" pipe loop, where a centreline weld crack was artificially introduced using the spark erosion method. It was shown experimentally that a signal change of <1% CSC can be reliably detected using a permanently-installed monitoring system and advanced baseline comparison algorithms.

*   Launched in April 1994, Insight is published monthly and is circulated worldwide to more than 65 countries around the world.

** Chua, C. A., Alleyne, D. N. & Calva M. (2017). Crack growth monitoring using low-frequency guided waves. Insight, 59(2) pp.64-71.
     This paper is available online from Ingenta.

The founding directors of Guided Ultrasonics Limited (GUL) were the innovators of Guided Wave Testing (GWT) and monitoring methods. Our commitment to developing state-of-the-art solutions for our customers has given the company the competitive edge necessary to maintain this leadership position. R&D is a continuous focus within the company, employing project results and customer feedback to keep the technology ahead of industry requirements. GUL equipment is designed to provide the best possible data so our clients can truly take advantage of the benefits of the GWT method.