In maintenance management of a painted steel railway bridge, appropriate corrosion prevention measures are needed. For establishing effective corrosion prevention measures, it is important to make clear classifications of coating degradation patterns. Accordingly we made a lot of observations on coating films of numerous bridges. The results of the observations showed that a coating degradation could be classified into some patterns, and that the coating degradation patterns (such as corrosion under coating, checking of coating, and peering of coating) were affected by construction environment and bridge ages.
Susceptibility to hydrogen embrittlement (HE) of austenitic stainless steels were investigated by Slow Strain Rate Testing (SSRT), both in gaseous hydrogen environment pressurized at 45 MPa and under electrochemical cathodic charging conditions. Test results were discussed based on estimated surface hydrogen contents of the unstressed steels into which hydrogen was charged under the same test conditions as SSRT. HE susceptibility of the steels in both gaseous hydrogen environments and electrochemical cathodic charging depended upon estimated surface hydrogen contents. Minimal of surface hydrogen content for HE were less than 10 ppm for 304L steel, and 100 ppm for 316L, respectively. The threshold value for 316L exceeded the content of hydrogen naturally absorbed from 45 MPa gaseous hydrogen environments, indicating that 316L has a sufficient resistance to hydrogen embrittlement in gaseous hydrogen environment pressurized at 45 MPa.
Transient of current in thin layer formation on nickel electrode was investigated during an anodic potential step in 0.1 M NaOH aqueous solution. The current was shown to have a time-dependency of i(t)=i0[1+(t/τ)]-1/2 which was derived from ionic migration under potential drop through the surface thin film. In the equation, the initial current, i0, and the time constant, τ, after the potential step were estimated from the slope and the intercept on the 1/i2 vs. t plot, respectively. From a plot of i02τ vs. φ, the oxide layer thickness at the potential, φ0, before the step and an average ionic mobility in the oxide film were calculated. The oxide layer was found to grow from the potential of 0.02 V vs. SCE and to saturate in thickness at 1.3 nm at the potential range between 0.2 and 0.4 V. The average mobility was estimated to be μ=9.9×10-20m2V-1s-1.
Since the control of corrosion by the addition of inhibitors is one of the key technologies for the adsorption refrigeration systems, the passivation behavior of an iron electrode in the 17.3 mol/kg LiBr+0.1 mol/kg LiOH solution containing molybdate and nitrate has been investigated at 428 K through electrochemical measurements and film analysis by radio frequency grow discharge optical emission spectroscopy (rf-GDOES). The results indicated that molybdate worked as a principal inhibitor in the system; molybdate was able to passivate iron without causing any pitting. However, the oxidizing power of molybdate was not sufficient to form a passive film on iron rapidly enough. The process could be assisted by the addition of nitrate; iron was passivated very quickly when the solution contained both molybdate and nitrate. Cares should be paid to that nitrate of higher concentrations could cause pitting especially when the concentration of molybdate was relatively low. The oxide films formed on iron in the presence of molybdate and nitrate were much thinner than those formed with only molybdate.