Development of AE Monitoring Method for Corrosion Damage of the Bottom Plate in Oil Storage Tank on the Neutral Sand under Loading

In Europe and USA, in-service diagnosis technique by AE method has already been used for evaluating the corrosion damage of bottom plate of oil storage tank. However, the diagnosis technique is dependent on the empirical method without physical bases such as the mechanism of AE generation due to the corrosion of bottom plates of oil storage tank. And also the relation between the corrosion rate and AE activity has not been clarified yet. This study was designed to clarify AE source and the relation between corrosion rate and AE activity during corrosion of bottom plate in oil storage tank, in particular, on the neutral sand bed. For modeling the corrosion condition which is similar to that of an in-service tank bottom on the neutral sand, the static stress of 382 MPa had been applied on the specimen plates. We investigated experimentally the relation between the corrosion rate and AE activity during the corrosion. Furthermore, the AE source and mechanism were examined based on the SEM observation of corroded surface. From these experimental results, the validity and physical basis for quantitative evaluation of corrosion rate by means of AE was presented.