The corrosion inhibition efficiencies of the oxygen decreasing treatment for mild steel and copper were evaluated through measuring corrosion rates of test coupons and corrosion potentials of electrodes hanging in the twenty three heat storage water tanks. The results of the evaluation, the corrosion rates of mild steel were reduced following DO concentration decreasing. In case of copper, most of case, the corrosion rates of test coupons showed the tendency of corrosion rate reduction following DO decreasing and the corrosion potentials of copper electrodes were less than 140mV (SSE). But, at two hot water tanks in which less than 0.5mg/L of DO concentration, the corrosion potentials of both copper electrodes increased to 220mV (SSE) and the corrosion rates of test coupons showed higher than the rate at DO saturated water.
The purpose of this investigation is to find a highly accelerated corrosion evaluation method which shorten the evaluate time of the corrosion resistance of electronic components having housing structures in which silver conductor formed circuit substrates are contained and are sealed with silicone. We applied three test conditions using three gaseous species such as SO2, H2S, and S8, respectively. We adopted in SO2 test(3300ppm/40℃/100%RH), H2S test(60ppm/40℃/100%RH) and S8 test(4ppm/90℃/<10%RH), respectively. As a results of the observations and analyses of the tested samples, it was found that the test using S8 showed the highest corrosion rate among those using three kind of gases. This high corrosion rate of S8 was estimated in conjunction with the higher permeability of S8 through silicone and corrosivity of S8 itself.
We investigated the effect of hydrogen absorption conditions on hydrogen desorption behavior of Ni-Ti superelastic alloy with cathodic hydrogen charging in 0.9％ NaCl solution. The amount of desorbed hydrogen at low temperature (～200 ℃) increased with increasing cathodic current density. It is likely that the increment of the amount of desorbed hydrogen at low temperature was due to the increment of the amount of hydrides formation. Vickers hardness in the vicinity of the surface of the alloy also increased with increasing cathodic current density. This is probably due to the hydrides formation in the vicinity of the surface of the alloy. These results suggest that hydrogen concentration in the vicinity of the surface of the alloy increased with increasing cathodic current density, i. e., increasing the amount of generated hydrogen per unit time, thereby causing the acceleration of hydrides formation.
In order to prevent stress corrosion cracking (SCC) in stainless steel used as a structural material for various industrial plants, it is important to reveal the propagation behavior of the crack. For the purpose of pursuing the quantitative time dependence of developing cracks, the changes in both the depth and the aperture of identical crack with the SCC time was clarified by using X-ray computed tomography (XCT). The resulting outcomes contribute to elucidation of the SCC behavior as well as technological improvements on life prediction and materials design.
An all volatile treatment (oxidizing) (AVT (O)) is expected as countermeasures against flow accelerated corrosion (FAC) of carbon steel piping at a power plant. Dissolved oxygen (DO) in the feed water inhibits FACs while DO can cause local corrosions at high temperature. A hydrazine (N2H4) eliminates DO at high temperature. We discussed the FAC mitigation effect of AVT (O+N2H4) where N2H4 was added to the feed water under AVT (O) condition. From the corrosion test of carbon steel pipes in NH3 solution at 150 ℃ under the high flow rate condition, FAC inhibition effect of DO at 15 μg/L is indicated in the presence of N2H4.
Cyclic corrosion tests, consisting of 0.86 kmol･m－3 NaCl solution spraying, drying, and wetting process, were conducted using a crevice-structured spot-weld specimen of some stainless steels in order to clarify the relation between corrosion behavior and the amount of chloride accumulated into the crevice. The component of chlorides accumulated into the crevice was mainly sodium chloride, although far less amount of metallic chlorides were also contained. When the amount of chloride was reached at about 20 mmol･m－2 and the total amount of iron and chromium was reached at about 0.5 mmol･m－2 in crevice, the maximum corrosion depth in crevice of SUS436L and SUS444 increased as cycle number increased. In case of SUS304 and SUS316L, sodium chloride and metallic chloride that enough to be increased the maximum corrosion depth as cycle number increased were not accumulated into the crevice. It is necessary that chlorides which contains specific amount of metallic chlorides accumulate into the crevice for corrosion to proceed in the depth direction. The corrosion form in this study was pitting. It is considered that the crevice have a role of accelerating the accumulation of chloride.