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Ultrasonic multi-skip tomography for pipe inspection

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Author: Volker, A.W.F. · Zon, A.T. van
Type:article
Date:2014
Publisher: American Institute of Physics
Source:40th Annual Review of Progress in Quantitative Nondestructive Evaluation, QNDE 2013, Incorporating the 10th International Conference on Barkhausen and Micro-Magnetics, ICBM 2013, 21-26 July 2013, Baltimore, MD, USA, 1581 33, 1750-1756
Identifier: 513430
ISBN: 9780735412118
Keywords: Physics · Multi-Skip · Wave Field Inversion · Iterative methods · Nondestructive examination · Ultrasonic transducers · Flat-bottom hole · Forward modeling · Model parameters · Screening techniques · Tomographic inversion · Ultrasonic testing · Industrial Innovation · Fluid Mechanics Chemistry & Energetics · PID - Process & Instrument Development · TS - Technical Sciences

Abstract

The inspection of wall loss corrosion is difficult at pipe supports due to limited accessibility. The recently developed ultrasonic Multi-Skip screening technique is suitable for this problem. The method employs ultrasonic transducers in a pitch-catch geometry positioned on opposite sides of the pipe support. Shear waves are transmitted in the axial direction within the pipe wall, reflecting multiple times between the inner and outer surfaces before reaching the receivers. Along this path, the signals accumulate information on the integral wall thickness (e.g., via variations in travel time). The method is very sensitive in detecting the presence of wall loss, but it is difficult to quantify both the extent and depth of the loss. Multi-skip tomography has been developed to reconstruct the wall thickness profile along the axial direction of the pipe. The method uses model-based full wave field inversion; this consists of a forward model for predicting the measured wave field and an iterative process that compares the predicted and measured wave fields and minimizes the differences with respect to the model parameters (i.e., the wall thickness profile). Experimental results are very encouraging. Various defects (slot and flat bottom hole) are reconstructed using the tomographic inversion. The general shape and width are well recovered. The current sizing accuracy is in the order of 1 mm.