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Multi-skip tomographic inversion

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Author: Volker, A.W.F. · Bloom, J.G.P. · Lorenz, M.
Type:article
Date:2010
Publisher: AIP
Institution: TNO Industrie en Techniek
Source:37th Annual Review of Progress in Quantitative Nondestructive Evaluation, QNDE 2010, 18-23 July 2010, San Diego, CA, USA, 1335, 647-654
series:
AIP Conference Proceedings
Identifier: 442950
ISBN: 9780735408883
Keywords: Materials · Corrosion · Multi-Skip · Support · Tomography · Wall Thickness Profile · Wave Field Inversion · Industrial Innovation · Fluid Mechanics Chemistry & Energetics · PID - Process & Instrumentation Development · TS - Technical Sciences

Abstract

Inspection of corrosion at pipe support locations is difficult because of accessibility limitations. Recently a screening technique has been developed called Multi-Skip ultrasonics. The method utilizes a pitch-catch set-up. Shear waves are transmitted that reflect multiple times in the pipe wall, from which integral wall thickness information is obtained. The method turns out to be very sensitive in detecting the presence of wall loss, but it turns out to be difficult to determine the extent of the wall loss. If the extent is not known, only a conservative estimate of depth can be derived from the Multi-Skip signals, because of the accumulative nature of the change in arrival time due to wall loss. Multi-Skip tomography appears to be a promising method in addition to Multi-Skip screening as a follow-up inspection technique. It uses full wave field inversion to determine a wall thickness profile at a particular location of the pipe on the support. As with the Multi-Skip screening method, Multi-Skip tomography is applied with the transmitter and receiver on both sides of the pipe support location and waves traveling in the axial pipe direction. The wave field inversion consists of a forward modeling step that predicts the measured wave field after which an iterative comparison process with the actually measured wave field results in an estimate of the wall thickness profile under the support.