This paper describes an advanced diagnosis method by acoustic emission (AE) which can evaluate corrosion damage on bottom plates of above-ground storage tanks. Non-intrusive diagnosis for the bottom plates of tanks are desirable from the viewpoint of safety and economy. In Europe and the United States, AE diagnosis with qualitative evaluation method (hereinafter it is called as “conventional” AE method) was developed. The conventional AE method gives non-intrusive diagnosis for corrosion damage on the plate through risk matrix by four grades. In Japan, the conventional type is not suitable because quantitative evaluation is required by Japanese regulation. AE diagnosis with quantitative evaluation method (hereinafter it is called as “advanced” AE method) was developed. The advanced AE method can evaluate corrosion rate and area of severe corrosion. One of key methods regarding advanced type is the layout of AE sensors. AE sensors are installed on both of shell and annular plate. The layout contributes to improve accuracy of evaluation for source location, and, it is also effective to remove noise. The key methods were achieved to derive a referential curve for evaluation of average maximum corrosion rate. “Average-maximum corrosion rate” means average corrosion rate at the location which has maximum-depth during operated period. The advanced AE method is useful for planning of the maintenance prior to overhaul, because it enables asset owners to estimate volume of repair work and to prepare materials.

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