Atlas Co. Ltd.

Tank bottom plate inspection by AEPD is a screening inspection technology that can detect state of the corrosion without shutdown or removing the tank's contents. By attaching a removable sensor to the tank's annular part, it is possible to inspect in service without stopping the tank operation.

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1. Details of examination

- It is desirable to inspect, detect and quantify plate thinning while a tank is in operation.

- It is desirable to confirm tank bottom condition without stopping the operation.

- The quality of tank content is likely to be oxidized when a tank is opened.

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  - Some method to inspect a tank bottom plate without opening the tank is requested.

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2. Inspection and analysis procedures

①. Sensing-pins and electrodes are placed on an annular plate around a tank.

②. Potential differences (PD) between each paired sensing-pins are measured bi-directionally.

③. PD in a sound condition is calculated by using finite element method (FEM).

④. PD change rate is calculated using PD obtained from ② and ③.

⑤. In order to solve the simultaneous equation, PD change rate of each lattice is obtained.

⑥. PD change rate of each lattice is collated with the mastering curve. Thereby, the thickness distribution is obtained.

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