Experimental studies on influencing factors of stress corrosion in rectifying column

Stress corrosion is the main factor that results in corrosion and fractures of rectifying columns in the process industries. Stress corrosion of rectifying columns can result in significant economic losses to chemical industries, while also having a major impact on the quality of products produced, particularly polysilicon. This gives rise to the need for research involving stress corrosion of rectifying columns. Corrosion coupons, including those with welds and bends, were used to simulate various stress conditions of stainless steel. For the experiments, a 1.5 wt.% hydrochloric acid and 2.5 wt.% sodium chloride solution was prepared to simulate realistic working conditions for the steel. The experimental methods include static coupon experiment, electrochemical experiment, scanning electron microscope and X-ray diffraction. The corrosion products of the coupons consisted mostly of grey-green materials with loose surface layers and small amounts of black matter. The corrosion products were confirmed to be FeCl₂ and Fe₂O₃, and the corrosion degree of the bent 20° coupon was found to be greater than that of other types of coupons. Under low temperature conditions, the corrosion rate of the coupons initially decreased over time before increasing and then decreasing again. At high temperatures, the corrosion rate began to decrease earlier than at low temperatures. The bending tendency of the 20° hanging piece was the greatest and that of the 30° hanging piece was the smallest. Higher temperatures promoted stress corrosion, with increases in temperature resulting in more significant corrosion effects. The results reported herein provide a theoretical basis and technical guidance for important anticorrosion and safety designs for distillation columns to be used in the semiconductor polysilicon rectification process.