3.1. High temperature corrosion/oxidation
Fig. 3 shows weight change of mild steel versus testing time curves at various temperatures in wet air and water steam environments. The weight gains were nearly the same between the environments of wet air and water steam. It can be seen that the relations between testing time and weight gain are linear on a logarithmic scale. The slope of the linear curves was about 0.58 irrespective of temperature and environment. The slope of the broken line which shows the weight loss at 773 K was also same as that of the weight gain curves. Fig. 4 shows weight gain behaviour in various high temperature corrosive environments of water steam with 0.5 and 10 vol.% hydrogen chloride, also including the weight loss at 773 K and in the 10 vol.% hydrogen chloride environment. A similar behaviour of weight gain versus testing time curves was observed both in Fig. 3 and in Fig. 4. The slopes of the linear curves under the corrosive environments were slightly higher than those under the wet air or water steam environment. The behaviour of the increase in film thickness with testing time is shown in Fig. 5. It was found that the relations between testing time and film thickness were the linear curves with the same slopes on logarithmic scale as the weight gain and loss ones under each corrosive condition, although the plots deviated from the linear curve at 773 K and 0.5 vol.% hydrogen chloride.