Attention should be paid to sulfur corrosion damage in the high-temperature pipelines of atmospheric and vacuum distillation units in the petrochemical industry
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A perforation in the pipeline behind a valve in the viscosity reduction line of a petrochemical company’s atmospheric and vacuum distillation unit caused a fire, leading to the shutdown of the atmospheric distillation section. The material of the accident line is grade 20 steel, with an original thickness of 7 mm; after 2 years of use, the corrosion rate reached 3.5 mm/year. The corrosion in the residue system is mainly high-temperature sulfur corrosion. The sulfur content in the residue of this company is 1.2%. The flow state has a significant impact on high-temperature sulfur corrosion. When the flow rate increased from 0.32 m/s to 0.8 m/s, the corrosion rate of carbon steel increased by a factor of 1.62. The sludge flow rate in the accident section was 0.3 m/s. Under normal operating conditions, the valve opening was less than 1/2, resulting in the smallest fluid cross-section and the highest flow rate (around 0.8 m/s) at a certain distance downstream of the valve. This caused severe corrosion of the pipeline in that area, leading to perforations. Therefore, more corrosion-resistant materials should be chosen. For example, Cr5Mo can be used for pipes, while 18.8 grade stainless steel can be used for elbows and pipes downstream of valves.
In petrochemical plants, high-temperature sulfur corrosion is a common problem, especially in residue systems. High temperatures and high sulfur content can cause carbon steel pipes to corrode rapidly. For example, at a petrochemical company, a No. 20 steel pipeline that had been in use for two years developed perforations due to high-temperature sulfur corrosion, which led to a fire. To prevent such accidents, more corrosion-resistant materials can be used to replace the existing carbon steel pipelines, such as Cr5Mo steel or 18.8 grade stainless steel, especially in areas with high flow rates and high corrosion risk, such as the pipelines downstream of valves. At the same time, the flow rate during operation should be controlled properly to prevent corrosion from being exacerbated by excessive flow speeds. .