Development of Improved AE Evaluation Technique for Corrosion Damage in Bottom Plates of Above-ground Oil Tanks in Service

摘要

AE diagnostics are widely used as a tool to conduct surveys and experiments in order to understand the characteristics of corrosion damage in the bottom plates of above-ground oil tanks worldwide. However, AE diagnostics have not yet become common as an on-site application at Japanese refineries because the degree of corrosion rate of tank bottom plates has been modest (<0.1 mm/year) and the conventional methods of corrosion management which use data collected periodically under the fire defense law, are widespread in the industry. On the other hand, the overall plate thickness measurement method of tanks using non-destructive inspection technology called Ultrasonic Testing (UT) has recently become popular. UT has been used to measure the thickness of above-ground tank bottom plates undergoing planned maintenance, so has enabled assessment of corrosion damage. In addition, the accuracy of the diagnostic technique using AE has been improved by advances in the specification of source location through increased accuracy in collecting the predominant AE signals based on improved denoising techniques. Overall UT measurement instead of discrete UT measurement has enabled confirmation of the accuracy of AE and assembling databases has enabled quantative evaluation of AE. Accordingly, we have improved the old principles of testing and evaluation methods, and developed a new method for detecting corrosion rate in tank bottom plates in service. By using the improved AE technique, we were able to obtain a good correlation between the data collected by the method and the status of corrosion rate in tank bottom plates. We describe the AE evaluation technique and we present the recommended practice for AE diagnostics.