Basic electrode reactions for the entry of hydrogen into metals under aqueous environment have been reviewed. Some analytical models that determine the parameters in the kinetics of the entry of hydrogen, including the hydrogen surface coverage and absorbed hydrogen concentration, are presented. On corrosion processes, the significance of surface film for the entry of hydrogen is emphasized from both the structure of the electric double layer at the electrode/electrolyte interface and under-potential deposition of hydrogen.
Stress corrosion cracking (SCC) susceptibility of commercial type 316L stainless steel (SS) and 316 SS hot rolled plates was examined by the creviced bent beam method in oxygenated high temperature water at 561 K. Asreceived type 316L SS and 316 SS showed the highest susceptibility to SCC at the cold rolling reductions of 10% and 20%, respectively. Aging treatment on type 316L SS had a beneficial effect of mitigating SCC, although the same aging treatment degraded SCC resistance of type 316 SS in a certain temperature range probably because of the combined effect of sensitization. The fracture surface of as-received and cold rolled type 316L SS and type 316 SS consisted mainly of inter-granular SCC with a small fraction of trans-granular SCC similar to those observed in the actual components. Heavily cold rolled Type 316 SS showed a large fraction of trans-granular SCC even in sensitized condition, suggesting that the heavy cold rolling formed active paths much sensitive to SCC than Cr depleted zone in crystal grains. It was suggested from SEM observation that the crack growth process on specimen surface would contain coalition of several smaller cracks to one larger crack in addition to the growth of each crack.
Corrosion damage of floor plates of a naphtha storage tank was monitored by acoustic emission (AE). AEs from the fracture of rusts were monitored by AE sensors of 30 and 50 kHz resonant frequencies, mounted on the terrace of annular plates and the side wall. AE signals were separated from noise by the waveform inspection. The signal counts from the sensors on the terrace were larger than those from the side wall sensors, and submitted to the location estimation of corrosion zone. The ratio of AE signals to total AE events were as low as a few percent. Source locations of the Lamb wave AEs detected by the AE sensors on the terrace of annular plates were estimated by three methods and ranked into three levels depending on the determination accuracy of the arrival times. Four portions in the third quadrant of the tank bottom were located as corrosion zones. They appear to be spreading from the zone with relatively large reduction of wall thickness measured in 2003. This paper also discusses some future problems of condition monitoring of huge steel structures by AE.
The results of exposure test by using the test piece which simulates cathodically protected marine steel structure are reported. The cathodic current in the tidal zone was measured. The average current density of cathodic current during a cycle of tidal range was calculated, and the relationship between long term change of the average current density and atmospheric temperature was investigated. The corrosion rate of carbon steel and the weight loss of aluminium anode were investigated. The weight loss of aluminum anode calculated from the average current density was almost equal to the experimental value.