In order to obtain metal materials that are resistant to erosion and corrosion, erosion and corrosion of the copper alloy JIS BC 6 in flowing water was observed at different flow velocities, water temperatures and content of oxygen dissolved in the water. The results were compared with those obtained using gray cast iron (FC 20) and austenitic cast iron (FCDA-Ni Cr 20 2). The weight loss of the copper alloy was found to be more dependent on the flow velocity and the content of dissolved oxygen in the flowing water than on the temperature of the water. In the early stages of flow after immersion, a thin layer composed of Cu(OH)2 and CuO was formed on the surface. But in the later stages, a strong, thick film composed of Cu(OH)2, CuCl2 and CuO was formed. Erosion and corrosion of the copper alloy, therefore, was governed by oxygen diffusion through the oxidized film. The copper alloy was more resistant to erosion and corrosion than both the gray cast iron and the austenitic cast iron.
Corrosion and dissolution behaviors of hot-pressed Si3N4 ceramics at 88°C in lithiated and borated water that was prepared to simulate PWR primary coolant were studied using a small once-through type experimental loop. Experiments were carried out for two Si3N4 ceramics with different sintering aids composed of MgO and Y2O3/Al2O3, respectively, and also Al2O3 which is used as the component of the mechanical seals for PWR primary coolant pump. The weight loss of exposed Si3N4 specimen containing MgO was relatively large and reached to 2.1mg/cm2 after 1, 000h exposure. Mg was dissolved selectively into the test solution, but dissolution of Si3N4 grain itself was estimated to be negligibly small. The surface was deeply corroded with the depth of 70μm, and changed to porous one. On the other hand, the weight loss of 1, 000h exposed specimen containing both Y2O3 and Al2O3 was very small at around 0.12mg/cm2. This value was nearly equal to that of Al2O3 ceramics. Similar to the case of Si3N4 containing MgO, Y was dissolved selectively and the surface was changed to porous. The corrosion depth, however, was small, of the order of 2μm. It was thus estimated that the corrosion resistance of Si3N4 ceramics in hot water was largely dependent on the compositions of sintering aids.
Moisture adsorption on the iron surface and its effect on corrosion were examined by quartz crystal microbalance (QCM) and thermal desorption spectroscopy. Reaction of water with the clean iron surface was examined by atom-probe. Amount of H2O adsorption increases sharply at 80% relative humidity (RH). Heat of adsorption is estimated to 11.2kcal/mol, which is close to the heat of vaporization of water and the critical number of monolayer, which exhibits the characteristics of bulk water is five. These results may suggest that adsorbed water forms localized water clusters rather than uniform film on the surface. The iron surface appears to be covered with OH in a form of Fe(OH) or FeOOH and water molecules are adsorbed on top. The oxidation rate also depends on RH and sharply increases at 80% RH.
Through the chemical analysis of the environment of smoke stacks and down-hole for thermal power plants, it was clarified that sulfuric acid dew point environment was the one where there were much amount of Cl- and Fe3+ with the range of 10-1000ppm besides H2SO4. Then, effect of Cl- and Fe3+ and alloying contents (Cr, Ni, Mo, Cu and N) on corrosion behavior of various stainless steels in H2SO4 environment were studied by immersion test and polarization curve measurements. By analyzing these data, corrosion rate of stainless steels in 50mass% H2SO4 with 1000ppm Cl- and Fe3+ can be expressed as the following general corrosion resistance index (GI); GI=-[Cr]+3.6[Ni]+4.7[Mo]+11.5[Cu].
Acid rain is the reason for the recent forest damage and acidification of soil as well as lakes. Sulfur dioxide in the atmosphere dissolves in water droplets to react with oxygen to form acid rain. Greater attention should be made to transfer technologies for removing SO2 and NOx from flue gas.
The C-0.5Mo and Cr-Mo low alloy steels have been widely used for high temperature and high pressure hydrotreating reactor vessels in the petroleum industry. Material degradation problems during the long term services are present concerns regarding the reliability of the pressure vessels. Recently, to improve the material resistances against long term hydrogenation services, advanced type Cr-Mo steels with higher design stress and modified alloy compositions has been developed and certified in the ASME B & PV Code. In this paper, present topics of the study on material degradation problems such as creep cracking, hydrogen attack and hydrogen embrittlement will be reviewed for conventional and advanced type pressure vessel steels.