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Reducing False Calls When Scanning for Internal Corrosion Using the Echo to Echo Technique with Compression Ultrasonic Waves: Part 1

Although it may seem simple at first, detecting and correctly classifying internal corrosion has proven to be quite a complex skill to acquire and master, even to the most experienced of technicians. Time and resources are used to re-inspect false calls. The problem lies when the NDT technician detects a reduction in wall thickness on the vessel or piping and is unable to supplement the finding with an alternative method or technique such as radiographic or visual testing. Using two or more methods/techniques to confirm an indication is good engineering practice. Since most false calls are attributed to laminations and inclusions, we will look at ways of differentiating laminations and inclusions from internal corrosion. These laminations and inclusions existed in the component from the initial manufacturing stage so are not necessarily detrimental to the component’s service life. In this first part of a two-part series, we will look at the basic outline of corrosion detection theory and what practical options are available to an ultrasonic technician working in the field.

References

ASNT, 2002, Nondestructive Testing Handbook, third edition: Vol. 4, Radiographic Testing, American Society for Nondestructive Testing, Columbus, OH.

ASNT, 2007, Nondestructive Testing Handbook, third edition: Vol. 7, Ultrasonic Testing, American Society for Nondestructive Testing, Columbus, OH.

Drury, J.C., 1997, "Corrosion Monitoring and Thickness Measurement - What Are We Doing Wrong?” available at silverwingndt.com/wp-content/uploads/2018/03/ultrasonics_corrosion_pitting.pdf.

Pellegrino, Bruce A., and Michael J. Nugent, 2015 (access date), “Nondestructive Testing Technologies and Applications for Detecting, Sizing and Monitoring Corrosion/Erosion Damage in Oil & Gas Assets,” accessed from http://sensornetworkscorp.com/wpcontent/uploads/2015/02/NDT-and-Corrosion-for-OGRev-2.pdf on 15 December 2015.

Trethewey, K., and J. Chamberlain, 1995, Corrosion for Science and Engineering, 2nd edition, Longman Scientific & Technical, London, England.

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