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Reducing False Calls When Scanning for Internal Corrosion Using the Echo to Echo Technique with Compression Ultrasonic Waves – Part 2

In Part 1 of this article, we looked at how corrosion is a significant problem for end users, especially in the oil and gas industry, and looked at some of the hurdles encountered by ultrasonic testing (UT) technicians when scanning for internal corrosion. Phased array ultrasonic testing (PAUT) was identified as the most effective technique to be used in corrosion detection, measurement, and morphology, but has increased costs involved with it. For the client, to send out different technicians to retest components multiple times is a very costly expense (requiring helicopters, boats, accommodation, and so on), so it is imperative that during the initial inspection the technician classifies any detected indications correctly, thus avoiding any unnecessary follow-up visits. In Part 2 of this article, we will look at classifying indications seen on the A-scan display of the UT machine using a zero degree twin crystal probe due to its widespread availability and cost effectiveness. We will also look at two cases (as shown in Figures 1 and 2) where wall loss was reported initially as internal corrosion but was later reviewed as either inclusions or laminations after numerous follow-up inspections. Figure 1 is a glycol suction scrubber where internal corrosion was reported next to the inlet nozzle on the shell, and Figure 2 is a firewater pump start air receiver where internal corrosion was reported on the blind flange.

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