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• Corrosion coupons bent different angles can simulate the column material under different stress conditions. • The corrosion degree of the coupon with 20° bend is higher than other coupons. • In the study time range, the corrosion rate first decreased, then increased and finally decreased. • In a certain temperature range, the temperature can promote the corrosion rate of 316 L stainless-steel. 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 FeCl 2 and Fe 2 O 3 , 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. [ABSTRACT FROM AUTHOR]

• An accident on corrosion of a polycrystalline distillation column was investigated. • The main corrosion forms are pitting corrosion and stress corrosion caused by Cl−. • Corrosion rate of 316 L stainless steel is negatively correlated with the pH. • Corrosion rate of 316 L stainless steel is positively correlated with temperature. • Transformation from pitting corrosion to stress corrosion occurs at high temperature. Distillation column is a fundamental device for the production of the semiconductor polysilicon. Therefore, investigating corrosion leakage protection of the distillation column is of great significance because of the undetectable yet very significant consequences of corrosion leakage to the column. In this work, corrosion investigation of a polycrystalline silicon rectification tower is presented. The composition and crack morphology of the distillation column (316 L austenitic stainless steel) were detected and analysed using component and hardness analysers. The effects of pH and temperature on the corrosion rate were studied by conducting electrochemical experiments. According to the macroscopic test results, the surface of the tower was covered with a large number of pits and cracks of different depths. Furthermore, based on the metallographic analysis, SEM analysis, and energy spectrum analysis results, it was determined that the crack morphology was mostly intergranular and transgranular. Combined with the test data and process environment, it has been determined that the main forms of corrosion for rectification towers are pitting corrosion and stress corrosion caused by chloride ions. According to the results of electrochemical experiments, the corrosion rate of 316 L stainless steel is negatively correlated with pH value for a pH range of 4–6 at constant temperatures. However, the corrosion rate is positively correlated with temperature for the range of 60 °C–90 °C at constant pH values. From the analysis of the corrosion morphology, the corrosion failure mode of 316 L stainless steel is largely attributed to pitting corrosion when the column is operated at low temperatures (60 °C and 70 °C). However, at high temperatures (90 °C), a transformation from pitting corrosion to stress corrosion occurs along the crystalline form. To ensure the stable operation of the polysilicon rectification tower, this paper proposes corrosion protection measures based on the results of the analysis as described. [ABSTRACT FROM AUTHOR]

• An accident of pipeline rupture in alkylation unit was investigate. • The failed pipeline structure provides conditions for hydrofluoric acid corrosion. • The decrease of pipeline strength is the direct cause of the accident. • The key factors to prevent pipeline leakage in alkylation unit were investigated. Owing to the corrosive, flammable, and explosive properties of pipeline materials in alkylation units, corrosion failure may result in leakage, fire, and explosion accidents. A bursting accident occurred in the 90° elbow of an alkylation unit pipeline. Failure analysis was performed by macroscopic analysis, metallographic analysis, chemical composition, corrosion form analysis, and corrosion product analysis. Finite element software was used to analyse the flow velocity, turbulence intensity, pressure, and wall stress distribution. The fault tree was combined with the analytic hierarchy process to realise the transformation of the structural importance-judgement factor-judgement matrix and to weight the events that may cause device corrosion failure. The results showed that uniform corrosion and stress corrosion of hydrofluoric acid occur in the pipeline and uniform corrosion is the dominant effect. Hydrofluoric acid corrosion leads to severe thinning of the pipe wall, making its strength drop below the bearing strength and rupture occurs. Quality of internal anticorrosion coating, water content of the medium and working temperature are the key factors to prevent pipeline leakage in alkylation unit. [ABSTRACT FROM AUTHOR]