Corrosion mapping by ultrasonics is a nonintrusive (noninvasive) technique which maps material thickness using

ultrasonic Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...

techniques. Variations in material thickness due to

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

can be identified and graphically portrayed as an

image An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...

. The technique is widely used in the oil and gas industries for the in-service detection and characterization of corrosion in pipes and vessels. The data is stored on a computer and may be color coded to show differences in thickness readings. Corrosion may be mapped using Zero degree ultrasonic probes, an

Eddy current Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a mag ...

array and/or Time of flight detection methods. The book ''Nondestructive Examination of Underwater Welded Structures'' by Victor S. Davey describes a "fully automated dual axis robotic scanner used for corrosion mapping normally using a single zero degree compression probe scanned in a raster pattern over the area of interest." He also goes on to explain that "typically a 4 mm by 4 mm raster" is used.

References

* Computer modelling for the prediction of the probability of detection of ultrasonic corrosion mapping Authors: Burch, S F; Stow, B A; Wall, M * Eddy current array probe for corrosion mapping on ageing aircraft AIP Conf. Proc. 509, pages 489–496; 8 pages) REVIEW OF PROGRESS IN QUANTITATIVE NONDESTRUCTIVE EVALUATION: Volume 19 Date: 25–30 July 1999 Location: Montreal (Canada) Rémi Leclerc and Rock Samson * Pipeline Corrosion and Cracking and the Associated Calibration Considerations for Same Side Sizing Applications Ginzel, R.K. & Kanters, W.A. Eclipse Scientific Products Inc, Williamsford, Ontario, Canada https://web.archive.org/web/20160304064220/http://www.turkndt.org/sub/makale/ornek/Pipeline%20Corrosion%20and%20Cracking%20and%20the%20Associated%20Calibrati.pdf * Improved plant availability by advanced condition based inspections Harry J.M Hulshofa, Jan W Notebooma, Paul G.M Welberga, Leo E de Bruijnb KEMA Nederland BV, P.O. Box, 9035 6800 ET Arnhem, The Netherlands Benelux Generation N.V., Rotterdam, The Netherlands Nondestructive testing Corrosion {{corrosion-stub