The Reflection of Guided Waves from Multiple Flaws in Pipes
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The Reflection of Guided Waves from Multiple Flaws in Pipes Ruth M. Sanderson · P.P. Catton
Received: 9 April 2013 / Accepted: 8 July 2013 / Published online: 26 October 2013 © TWI Ltd. 2013
Abstract Inspection of pipes and pipelines for corrosion is vital for their safe and cost effective operation. Ultrasonic guided wave inspection is a relatively new technique used for this. Recent research has advanced the technique so that it may be possible to characterise individual flaws, making guided waves a potentially viable alternative to direct examination where internal in-line inspection (ILI) is not feasible. However, corrosion often occurs in clusters and the presence of one flaw could affect the signals received from subsequent flaws. Therefore, the issue of multiple flaws must be dealt with if flaws are to be adequately characterised in the field. In order to address this, a semi-analytical modelling methodology has first been developed for the reflection and transmission of guided waves from a single flaw and then, this has been combined with an analytical model for wave propagation to extend it to simulate the reflections from two or more flaws. The semi-analytical model for two flaws has been validated by comparison with experimental data and verified against three-dimensional finite element simulations. Keywords Analytical models · Inspection · Pipelines
R.M. Sanderson (B) TWI Ltd., Granta Park, Great Abington, Cambridge CB21 6AL, UK e-mail: [email protected] P.P. Catton Centre for Smart Infrastructure and Construction, Institute for Manufacturing, Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK
1 Introduction The guided wave inspection technique has the significant advantage over other techniques of full volume inspection of tens of metres of pipeline from a single test location [1–3]. However, there are often many different features present in the pipe which affect the guided wave signals such as welds, flaws, pipe supports and coatings. The presence of these features adds complexity to the received signals making interpretation of the inspection results difficult. The technique was originally a screening procedure with only an approximation of the loss of cross-section and axial location of the corrosion given, but recent research has shown that it may be possible to characterise isolated flaws [4]. However, corrosion type flaws are often not found in an isolated region but are more likely to exist as a cluster of flaws [5]. Therefore, the signals from a given flaw are likely to have passed through other features such as other flaws or welds before being received. It is therefore important to understand and quantify the interaction between multiple features. If the guided wave inspection technique is being used solely as a screening procedure, the effect of this is likely to be negligible in most cases. However, with the increasing use of refined signal processing procedures to give more information about the flaws detected, intelligibility of the sig
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