The research work of SCC of stainless steel has been done again after interval of 30 years. In order to study the SCC different from usual method, development of various devices and techniques were done. The most important device among them is the super Kelvin force microscope. It has been succeeded that the deformation behavior of crack with the crack propagation was observed and that the hydrogen compound behavior was observed as the potential distribution by using this device. It has been proved that the crack propagation of SCC of stainless steel on chloride environment occurs during the movement of hydrogen in stress field.
Copper tubes were immersed for up to 18 months in synthetic freshwaters containing silica to investigate the effect of silica, chloride and sulfuric ion on corrosion behavior and pitting morphology of copper. Pitting corrosion similar to the moundless type pits occurred on the surface of the copper tubes immersed in the water containing 20 or 40 ppmSiO2, 10 ppmCl− and 10 ppmSO42−. The surface of the copper tube immersed in the water containing 80 ppmSiO2 was covered with white granular scales. The depth of pitting corrosion occurred in the water containing 80 ppmSiO2 was smaller than those of pits occurred in the water containing 20 or 40 ppmSiO2. The concentration of silica in the synthetic water containing 20 ppmSiO2 decreased to about 2 ppm for 9 months when the copper tubes were immersed in the synthetic water.
Finite element analyses were conducted to evaluate stress corrosion cracking (SCC) growth behavior based on J integral. The simplified method to calculate the J integral for four-point bending test was proposed. The J integral was calculated based on load-displacement curve and strain at the surface of tensile side in the proposed simplified method. The stress distribution ahead of crack tip was normalized by the J integral irrespective of loading condition and crack length. Thus, the J integral was effective for evaluation of SCC growth behavior.
Effect of flow condition on NH4HS corrosion was studied by analysis of a corroded elbow sample and computational simulation. The thickness of corrosion products film formed on the inner surface of the elbow was measured and chemical composition of the film was analyzed using EPMA (Electron Probe Micro Analysis). In addition, flow pattern prediction and CFD (Computational Fluid Dynamics) analyses were employed. The center of the outer radius of the elbow was preferentially corroded in the sampled elbow. The film on the outer radius of the elbow was thinner than the inner radius and contained less sulfur than the inner radius. Based on three CFD models, it was found that the liquid volume fraction increased in the center of the outer radius of the elbow. Thus, corroded area was consistent with the area of high liquid volume fraction. Furthermore, a calculated wall shear stress on the outer radius was much higher than the inner radius from CFD results. Therefore, it was concluded that a protective iron sulfide film could not be formed on the outer radius due to a high wall shear stress.
It is verified that corrosion resistance of pre-coated steel sheets, coated with various coating materials, is mainly depended on thickness of topcoats, a type of anticorrosive pigments used in primers and an amount of accumulated salinity thorough a set of 44 months outdoor exposure tests. Results of the exposure tests showed almost no correlation with test results in the test conducted according to salt splay test and CCT-JASO-M609, widely accepted as an accelerating test method for evaluation of corrosion resistance. A series of analysis with SEM and EPMA on sections of edge creep area has revealed that there is a clear difference in corrosion development between these test methods. Since the salt splay test and CCT-JASO-M609 specifies a test condition where corrosion products cannot easily prevent further proceeding of corrosion, we presume that sacrifice corrosion cells composed of steel and plated steel substrates can stably exist for a long time in the test according these accelerated corrosion tests.