The collection of the actual damage data and statistical analysis are introduced by some case studies in order to apply them to the practical maintenance in chemical plant. In the case of the radiation tube with oxidation, the inspection data were grouped by the actual damaged condition and the life prediction by the statistical analysis was conducted. From the result, the replace plan was clarified. In two case studies on external corrosion, the corrosion data and associated information were collected from the actual plant and statistical analysis was conducted. From the result, the acceleration factors of the external corrosion were quantitatively clarified by the distribution of the corrosion rate. Based on the results, the technical module was developed. And in actual plant, the inspection was planned and carried out. From these case studies, it is recognized that understanding the characteristics of the degradation is important for the statistical analysis of damage data.
To obtain the knowledge about the corrosion ability and its mechanism as a target the soil environment microorganisms, lake mud was cultured with metallic iron. As a result, corrosion of carbon steel was observed with sulfate reduction and methane producing activity in brackish medium with lactate as substrate. The next-generation sequencing technologies revealed microbial community varies greatly between environmental samples (inoculated sample) and cultured sample. Particularly, Desulfovibrio species and Clostridia class, that sulfate reducing ability have been reported, became dominant. Inhibition test of sulfate reducing bacteria and methane producing archaea suggested that sulfate reducing bacteria plays a major role for this corrosion, and methane producing archaea enhanced corrosion activity by the coexistence of sulfate reducing bacteria.
Involvement of microorganisms to corrosion refers to microbiological influenced corrosion（ MIC）. We have previously succeeded a lab-scale corrosion test using bottom water from oil-storage tanks and shown microbial community change after the corrosion by a denaturing gradient gel electrophoresis analysis. However, those community structures have not yet been correlated to the accelerated corrosion. Therefore, we further conducted analysis of microbial community for by pyrosequencing using a next-generation sequencer. In the corrosion sample, an acetic acid bacterium Acetobacterium sp. and a sulfate-reducing bacterium Desulfovibrio sp. were enriched. In contrast, only Desulfovibrio sp. bacterium was enriched in the non-corroded culture, and Acetobacterium sp. bacterium was not observed. These results indicate that the Acetobacterium sp. bacterium may involve in the accelerated corrosion. This is first report of the corrosion by the Acetobacterium sp. bacterium. The combination of a lab-scale corrosion test and microbial community analysis by pyrosequencing would be useful to correlate between corrosion behavior and microbial community change. In future, such investigation would contribute to the understanding for the microbiologically influenced corrosion.
In order to shorten the time required for preparation of an ultrathin polymer coating on a passivated Fe electrode, a self-assembled monolayer of 16-hydroxyhexadecanoate ion HO(CH2)15CO2－ adsorbed on the electrode was modified with 1,2-bi(striethoxysilyl)ethane(C2H5O)3Si(CH2)2Si(OC2H5)3 and octyltriethoxysilane C8H17Si(OC2H5)3. Further, the passivated and polymer-coated electrode was healed by treatment in 0.1 M NaNO3. The time for passive film breakdown, tbd and the protective efficiency, P (%) were determined by monitoring the open-circuit potential and repeated polarization measurements during immersion in 0.1 M KClO4, 0.1 M NaNO3, 0.1 M Na2SO4 and 0.1 M NaCl for many hours. The tbd values were 57.4, >240, 19.2 and 9.0 h, respectively. Breakdown of the passive film was markedly suppressed by coverage with the polymer coating and healing treatment. The P values of the electrode in these solutions were extremely high, more than 99.9% before tbd, indicating that complete protection of substrate Fe against corrosion was accomplished by covering the electrode with the healed passive film and polymer coating unless the passive film was broken down.
Deterioration mechanism of corrosion resistance at heat-tinted zone of stainless steel weldment was studied. Local electrochemical measurements with micro capillary cell and surface analyses at small regions were conducted to correlate local variation in corrosion behavior and surface structure. Depletion of the Cr content at the substrate surface and formation of an Fe rich oxide layer on the surface were confirmed, although their distances from the welding bead were not identical. It was also revealed that the corrosion behaviors at the area with the Cr depletion and the area with the Fe rich oxide layer were different. The Cr depletion led to lowering of pitting potential due to the activation of substrate steel whereas the Fe rich oxide layer led to preferential rusting in the cyclic corrosion test due to deterioration of the surface protective layer.