Cut edge corrosion is well known problem at shear cut edge of galvanized steel sheet, where the zinc coating is consumed early. The cut edge corrosion is regarded as galvanic corrosion under a thin electrolyte film. A new numerical analysis model for galvanic corrosion has been developed in order to make clear the mechanism of the cut edge corrosion. This model has been considered oxygen concentration in the electrolyte, because the corrosion rate under a thin electrolyte film is controlled by oxygen dissolving from air. In addition, ion transportation and reactions are considered. This paper explains details of the numerical model and numerical analysis results.
It has been believed that ant's nest corrosion of copper tubes occurs only in moist vapor phase containing organic carboxylic acid such as formic and/or acetic acid. In this study, copper tubes were immersed in formic acid solution for 28 days to reproduce ant's nest corrosion of copper tubes in liquid phase. Ant's nest corrosion occurred in copper tubes immersed in 1, 5, 10, 100 and 1000 ppm formic acid solutions for 28 days, while the uniform attack occurred in copper tubes immersed in 10000 ppm formic acid solution. It was found that the initiation and propagation of ant's nest corrosion accelerate in the solution containing both formic acid and sulfate ion.
Methods evaluating the growing process of stress corrosion cracking (SCC) of 18Cr-8Ni (18-8) stainless steel (SS) in high temperature water were quantitatively investigated using the electric circuit model. In this paper, it was confirmed that effects of cold work and heat-affected zone (HAZ) of weld on crack growth rate (CGR) of 18-8 SS in high temperature water and the combined effects of cold work and sensitization could be estimated using equations regarding cold work from mathematical consideration of factors related to polarization resistance at crack tip.
Cl− is known to influence corrosion rate of girders of steel bridges. In general, precipitation rate of air-born salt is used to discuss the stability of steel bridges in a corrosion environment. However, residence time of Cl− on girder is considered to directly affect the corrosion of girders of steel bridges, while precipitation rate of Cl− is one of the factors in residence time of Cl−. In addition to precipitation rate of Cl−, in this study, the Cl− abundance on web and the quantity of Cl− removed from web due to rinsing with dewdrop on the girders were analyzed during February to May 2012, in order to examine the residence time of Cl− on the girder of the bridge. As a result, the residence time of Cl− on inside-ward web of the girder is calculated to be several tenths to several hundreds days. Though there is a possibility that fluctuation of Cl− precipitation rate during a month causes error of the residence time, the continuing analysis up to one year for the bridge probably make it possible to yields more reliable residence time of Cl− on the girder.
The coating film formation and the corrosion resistance of phenolic resin were examined as an alternative for chromate on the galvanizing steel sheet. The effect of cure temperature and phosphoric acid on film formation and corrosion resistance was investigated by thermogravimetry and differential thermal analysis (TG-DTA), surface energy measurement, and the coating film characterization by XPS and FT-IR analysis. The mechanism of corrosion resistance was estimated by the polarization measurement of the coating plate. The resin, which was in an aggregate state at 80°C, gradually became loose by thermal energy as temperature rose, and it self-cured above 130-150°C to make the film that gives good corrosion resistance. Addition of phosphoric acid to the phenolic resin solution has improved the corrosion resistance even at 120°C that is below the original self-cure temperature. Though the mechanism of the effect of phosphoric acid is not always clear, it was found that phosphoric acid promotes the cure of the resin and enhances the insolubility to the salt water. Also, it was confirmed that phosphoric acid itself is incorporated into the coating film. It seems that these facts improve corrosion resistance.