NDTsi 2001 Session: Advances in Non-Ultrasonic NDE Methods
Fundamental Examination of AE Detection in Oil Storage Tank Floors
I. Morita, ENAA, Japan; T. Arakawa, M. Tagami, T. Amano, IHI, Japan
ABSTRACT
At present, time-based internal inspection (every 8-10 years) is required in Japan for large above ground crude oil tanks due to the regulation based on the fire and disaster law, regardless of the grade of corrosion. However, in the case of a tank which has just been manufactured, the present condition is that there is no damage. In recent years, there has been a call to make a more rational evaluation technique available in Japan. Therefore, the application of a technique which evaluates the corrosion grade of tank floors with the AE method without opening the tanks during operation is desired. In the field of AE estimation of the corrosion of oil storage tanks, however, the mechanism of AE generation caused by corrosion has not been extensively reported. This study concerns a fundamental examination of "Research and development of tank floors corrosion diagnosis / evaluation technology during operation by the AE method" which The Engineering Advancement Association of Japan (ENAA) is performing over for four years under a contract from the Petroleum Energy Center (PEC) of the New Energy and Industrial Technology Development Organization (NEDO). The examination performed the corrosion acceleration examination by immersing the laboratory specimen in oxygen-rich 3.5% NaCl solution and loading current on the laboratory specimens. AE measurement is performed on these laboratory specimen varying the corrosion speed of the steel. These measurements showed: 1). Although the frequency of AE being generated is high in the initial stage of corrosion, after that, the speed of oxygen changing into an oxidization coating was rate-determining, and the frequency of AE generation decreases. 2). It is thought that the cracks generated by the expansion of the oxidization coating with the generation of the corrosion coating caused the AE generation. 3). The characteristics, such as corrosion AE waveform and frequency In addition, the examination by the mock-up tank with a diameter of five meters and the examination for applicability by the 100,000kl tanks are performed now.
Publication Source: 3nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, November 14-16, 2001, Seville Spain. Publisher: Tecnatom s.a. - [Homepage]
