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① Stress corrosion cracking (ammonia embrittlement) of carbon steel and low-alloy steels in liquid ammonia: Pure liquid ammonia does not cause stress corrosion cracking; however, when air (O2, N2, CO2) is present in the liquid ammonia – as is the case with agricultural liquid ammonia used in the fertilizer industry – stress corrosion cracking occurs, both in the liquid phase and in the gas phase. If the water content in liquid ammonia exceeds 0.2%, it can prevent cracking from occurring. Heat treatment to relieve residual stress in the welds is a necessary protective measure. ② Stress corrosion cracking of carbon steel in CO-CO2-H2O environments: Such damage incidents occur frequently in industries such as ammonia synthesis, hydrogen production decarburization systems, gas systems, organic synthesis, and petroleum gases. ③ Stress corrosion cracking of austenitic stainless steels in high-temperature water: Such damage incidents occur frequently in the industrial and nuclear industries. Dissolved O2 is a promoting factor; the cracks are intergranular, but if Cl- is present, the cracks will be transgranular. ④ Carbon steel is sensitive to stress corrosion cracking in nitrate solutions, gas-liquid mixtures, and coke oven gas. For example, in coke oven gas (composed mainly of CH4 and H2, with traces of CO2, H2S, NH3, HCN, and H2O), cracks appear after just one year of use at 35°C.