AE Global Diagnostics on Corrosion Damage in Bottom Plates of Above-ground Oil Tanks.

Abstract

This paper describes the results of development regarding AE global diagnostics on corrosion damage in bottom plates of aboveground storage tanks. It is sometimes difficult to evaluate the corrosion damage by conventional measurement methods such as HPIS because the measured AE data includes various noise. Regarding our study for the layout of AE sensors as double layer which are installed on shell plates, the removal of AE data reflected by bottom plates made it possible to identify a liquid drop noise from cone roof tanks. In addition, the accuracy of the identification of AE source was improved with the AE waveform classification processing. The AE data by shell and annular sensors could facilitate the removing of some noise to evaluate the location of corrosion. As well known, the corrosion risk parameter (CRP) is correlated with the actual corrosion rate obtained by the overall UT scanning system for thickness measurement of bottom plates. The CRP can predict the average maximum corrosion rate based on the actual measuring data. The average maximum corrosion rate can also be predicted with AE activity since the relationship between CRP and AE activity is verified by another study. The referential curve for prediction of the average maximum corrosion rate based on AE activity was developed as quantitative evaluation technique without opening tank under plant operation. The AE Global Diagnostics enables to plan of the maintenance before opening the tanks by determining the elements of repair work, preparing materials and establishing procedures for maintenance plan.