An ultrathin, two-dimensional polymer coating of carboxylate ion self-assembled monolayer adsorbed on a passivated iron electrode is prepared by chemical modification with alkyltriethoxysilanes. Passive film breakdown in 0.1 M NaCl, 0.1 M Na2SO4, and 0.1 M KClO4 with and without Cl− is markedly prevented by coverage with the polymer coating and healing treatment in 0.1 M NaNO3. Complete protection of the iron electrode against corrosion in these solutions is accomplished by covering the electrode with the healed passive film and polymer coating unless the passive film is broken down.
This study was carried out to clarify the SCC arrest behavior at the fusion line between Alloy 182 weld and low alloy steel based metal in distilled water under high temperature and high pressure conditions. The specimen used was low alloy steel based metal overlaid with Alloy 182 weld. CBB test was conducted in the autoclave at the temperature of 288°C, the pressure of 8 MPa, the electric conductivity of introduced water with less than 10 μS/m and dissolved oxygen concentration with 8 ppm. The results of CBB test were that all cracks were arrested at the fusion line and sphere-shaped oxide on low alloy steel based metal side were found. According to the relationship between the weld thickness of Alloy 182 and the oxide size, the larger weld thickness of Alloy 182 the larger the oxides become. It suggests that the galvanic effect caused by difference of potential between Alloy 182 weld and the low alloy steel based metal may have affected the results.
We studied corrosion of alloy steel which is used in oil well pipe under high temperature and CO2 environment. Corrosion tests of the specimens with different quantity of Cr addition was carried out. Cross section and surface morphology of corrosion products were analyzed by SEM and EDX. The corrosion products were changed from crystal state to film state by Cr increase in the alloy. The crystal form corrosion products were FeCO3, and EDX analysis showed that there were Cr concentration in the film form corrosion products. The dense structured Cr compound was formed by increasing Cr content in the alloy, and the corrosion resistance was improved by the suppressed dissolution of Fe in the dense structured Cr compound
The hydrogen embrittlement test of steel samples carried out. The loaded samples are immersed in an ammonium thiocyanate solution. Sub-cracks grew in the transverse direction to the loaded stress on the specimen surface. The most quick-growing crack may cause the fracture of specimen.
In order to investigate the corrosion of surface treated weathering steel bridges constructed more than 30 years ago, we conducted a visual inspection, a measurement of rust and coating thickness, a measurement of ion transfer resistance, cross-sectional observation by the reflected polarized light and EPMA analysis. The rust appearances of 57 points out of 78 were assessed normal by the visual inspection. Imbricate and layer-delaminated rusts were observed at the some ends of the bridge beam from which water used to be leaking. The rank of the rust appearance tends to decrease with an increase in the thickness of rust and coatings. The cross-sectional observation and EPMA analysis revealed that the condensed Cl existed at the bottom of the anomalous rust, while the optically isotropic layer of protective rust existed at the bottom of the normal rust.
In absorption refrigeration systems, it is necessary to maintain adequate concentration of inhibitor, especially that of molybdate, in an absorbent, i.e. concentrated LiBr solution, to keep the constructive materials free from corrosion damage. In order to propose an alternative to the current management method based on chemical analysis, electrochemical approach has been introduced for in situ analysis of molybdate in an absorbent in this study. Molybdate ions are successfully reduced on a glassy carbon electrode to give cathodic current which clearly depends on the concentration of molybdate. Because the cathodic polarization causes deposition of molybdenum (IV) oxide, successive anodic polarization is effective to quantify the amount of the deposits. Based on the redox phenomena of molybdenum species on a glassy carbon electrode as demonstrated in this study, the electrochemical technique can be applied to the practical management of adsorbent.
Stress corrosion cracking behavior around the interface between nickel base alloy (Alloy182) and low alloy steel (LAS) was investigated by modified large-scale CBB test method in high temperature oxygenated water. In the smooth test pieces, oxides formed in LAS or cracks propagate along the interface in pure water (<0.1 μS/cm at inlet), on the other hand, a crack propagated deeply into LAS in the environment where conductivity was controlled to approximately 0.3 μS/cm at inlet by Na2SO4 injection. In the latter case, the surface crack penetrates the width of the test pieces so that the mechanics conditions were thought to be severe. In notched test pieces, it was observed that cracks propagated into LAS and also oxides formed in the pure water. There was a tendency that the crack depth and the diameter of oxide increase with thickness of Alloy 182 increasing. The effect of applied strain and sample preparation direction to the welding direction on SCC behavior around the fusion interface was investigated, but there is no significant difference in the morphology by applied strain and sample preparation directions.
Depths of inclusions in low alloy steel (LAS) and morphologies at crack tip under various mechanics conditions were investigated by modified large-scale creviced bent beam (CBB) test method for alloy182/LAS clad test pieces in high temperature oxygenated water. Mechanics conditions were described by KJ values which are K values from elasto-plastic analysis. From the data in pure water, there was good relationship between depths of inclusions in LAS and KJ values. Considered from the data in pure water and sulphat-econtaining water, sustained crack growth was observed above 75 MPa √m of KJ and sulphate containing. It was thought that sustained crack growth needs higher the crack growth rate which is a function of KJ than the oxidized rate in LAS.
The corrosion mechanism and its modeling of Co-polyacetal (Co-POM) under nitric acid (HNO3) solution were investigated. The degree of degradation was evaluated by the changes in weight and molecular weight. The weight change in HNO3 solution was linearly decreased after the incubation period. From SEC measurements, it was observed that the occurrence of degradation of Co-POM by HNO3 solution was limited near the surface on a specimen, and the inside had remained original material. From this result, it was inferred that the degradation type of Co-POM by HNO3 solution is the corroded layer-forming type. The rate equation for corrosion by hydrolysis reaction between Co-POM and HNO3 solution was proposed with the rate constant for reaction which was calculated from molecular weight change of the surface on a specimen. The diffusion rate of nitric acid concentration was calculated from weight change (Wet–Dry in condition). Finally, the corrosion rate of Co-POM was estimated numerically by combining the concentration of diffused HNO3 solution into Co-POM over time and the previous equation for corrosion. This result of simulation agreed well with the experimental ones.