Corrosion by sodium hydroxide solution
Thread Content
Dear teachers, I would like to ask for your advice. Currently, the concentration of sodium hydroxide is 50%, and the temperature is 200 °C. It involves Ni6+Q345R composite plates, and cracks appear in the cladding welds of the equipment after just a few months. Even after repairs, cracks reappear after some time. What’s the reason?
After pipeline welding, stress is generated due to the heating and contraction of the welds. These stresses are quite high, leading to stress concentration, which affects the strength of the pipeline. They also serve as triggers for stress corrosion and hydrogen embrittlement, further reducing the pipeline’s strength. Therefore, post-welding heat treatment is required. Carbon steel and low-alloy steel are prone to stress corrosion cracking in the following media environments; both new and existing pipeline joints should undergo post-weld stress-relief heat treatment: soluble alkali solutions, ammonia water, amine solutions, spent amine solutions, lean and rich ethanolamine solutions, lean and rich DEA, lean and rich MDEA, as well as condensed oils ； Media such as acidic water, acidic gas, and sulfur-containing gases ； Oily wastewater containing humid H2S and sulfur-containing media ； Dew point corrosion media such as aqueous HCN solutions, wet C0-C02-air, and regenerated flue gas. I wonder if post-weld stress-relief heat treatment was performed?
Pay attention to the impurity content in the alkali, with precision to the ppm level