In Service Inspection by Acoustic Emission technique offers the user significant advantages, such as the capability of monitoring corrosion damage of the bottom plates of an oil tank without opening it. In this study, the mechanism of AE generation due to the corrosion of tank bottoms on strong acidic sand was examined. During the corrosion process, the corrosion rate and the AE activity were estimated and the relation between these two factors was examined. The sources of AE due to the corrosion of tank bottoms on an acidic soil were specified. Here, the physical foundations of a global diagnosis technique based on the AE method for evaluating the corrosion damage to tank bottoms were presented.
(Na, K)NO3 melts of various ratios were used as promoters for the partial oxidation of methane to methanol. Experiments were performed in a flow reactor system under atmospheric pressure and at various temperatures in the range of 525-600 °C. The influence of reaction temperature, melt composition, and reduced oxygen species on methane conversion and methanol selectivity were investigated systematically. The major reaction products were CH3OH, CO, CO2, and trace amounts of C2H6 and C2H4. A methane conversion of 1.8-12.4% and a methanol selectivity of 0.4-14.1% were obtained under these reaction conditions. Binary melts could achieve higher methanol selectivity than a single melt. The amounts of reduced oxygen species O2- and O22-were estimated from thermochemical data according to the ion equilibrium in molten nitrates. The promotive effect of nitrate melts was confirmed and the results indicate that superoxide O2- plays an important role for methanol formation.
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 inservice 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.
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