基于气液平衡条件下20#碳钢的冲刷腐蚀规律研究

发布时间：2018-06-06 08:44

本文选题：20#碳钢 + 气液平衡　；参考：《浙江理工大学》2017年硕士论文

【摘要】：20#碳钢是炼油行业中常用的设备及管道材料。由于原油劣质化的影响(氋硫、高氯、含氮),炼油过程中形成的腐蚀性介质(主要包括NH4HS和NH_4Cl)在一定流速下对设备管道造成严重的冲刷腐蚀,威胁装置的本质安全并造成重大的经济损失。冲刷腐蚀作为流动腐蚀的主要失效形式之一,具有明显的风险性和局部性难以防控,特别是酸性水系统管道冲刷腐蚀十分严重。冲刷腐蚀影响因素涉及化工工艺流程、设备结构、腐蚀性介质浓度、流速、温度、压力、运行工况,目前尚缺少系统的预测方法和研究体系,冲刷腐蚀失效事故仍频发。本文依托某企业酸性水系统冲刷腐蚀失效,针对典型材料20#碳钢开展气液平衡条件下冲刷腐蚀规律研究。根据现场实际运行工况,基于化工工艺过程采用Aspen工艺计算软件构建气液平衡、离子平衡和化学平衡模型,获得不同腐蚀性介质在气相及液相中的分布规律及溶液pH值变化趋势;结合Computational Fluid Dynamics(CFD)软件模拟计算多相流动特性分析冲刷腐蚀失效案例。结果表明:随着温度降低,腐蚀性气体在水中摩尔分率增大,冲刷腐蚀风险增大且水相分率高的位置,冲刷腐蚀失效严重;通过合理注水量可以有效增大pH值,减小冲刷腐蚀风险。运用旋转式冲刷腐蚀实验装置开展20#碳钢在腐蚀性介质NH_4Cl溶液中的腐蚀速率研究,包括:不同浓度、温度、流速(包含静止环境)等条件下冲刷腐蚀速率规律。同时采用扫描电子显微镜(SEM)技术观察腐蚀试件表面形貌,研究冲刷腐蚀过程和腐蚀机理,进一步明确20#碳钢在石化体系中出现腐蚀泄漏和穿孔失效的关键影响因素,为合理降低石化行业腐蚀失效提供理论依据。本文创新之处在于:针对酸性水管道现场实际运行工况,开展化工工艺过程关联分析并采用数值模拟与冲刷腐蚀实验相结合的研究方法构建酸性水管道腐蚀性溶液气液平衡环境,探究冲刷腐蚀表征测试方法和临界特性规律。研究成果可为石化行业设计优化、设备选材和失效分析提供理论支撑。
[Abstract]:Carbon steel 20 # is a common equipment and pipeline material in oil refining industry. Due to the influence of poor quality of crude oil (sulfur, high chlorine, nitrogen-containing nitrogen, corrosive medium (mainly including NH _ 4HS and NH _ 4Cl) formed in refining process), serious erosion corrosion is caused to the equipment and pipeline at a certain flow rate. Threaten the essential safety of the device and cause significant economic losses. As one of the main failure forms of flow corrosion, scour corrosion is difficult to prevent and control with obvious risk and locality, especially the erosion corrosion of acid water system pipeline is very serious. The influencing factors of scour corrosion include chemical process, equipment structure, corrosive medium concentration, flow rate, temperature, pressure and operating condition. At present, there is still a lack of systematic prediction method and research system, and scour corrosion failure accidents still occur frequently. In this paper, based on the erosion failure of acid water system in a certain enterprise, the erosion corrosion law of typical carbon steel 20# under the condition of gas-liquid equilibrium is studied. According to the actual operating conditions of the field, the models of gas-liquid equilibrium, ion equilibrium and chemical equilibrium are constructed by using Aspen process calculation software based on the chemical process. The distribution of different corrosive media in gas phase and liquid phase and the changing trend of pH value of solution were obtained, and the failure cases of scour corrosion were analyzed and calculated by computer rational fluid dynamic CFDs software. The results show that with the decrease of temperature, the molar fraction of corrosive gas in water increases, the corrosion risk increases and the water phase fraction is high, the erosion corrosion failure is serious, and the pH value can be effectively increased by reasonable water injection. Reduce the risk of erosion corrosion. The corrosion rate of 20 # carbon steel in NH _ 4Cl solution was studied by means of rotating scour corrosion test equipment, including: the law of erosion corrosion rate under different concentration, temperature and flow rate (including static environment). At the same time, scanning electron microscopy (SEM) technique was used to observe the surface morphology of corrosion specimens, to study the erosion process and corrosion mechanism, and to further clarify the key factors affecting the corrosion leakage and perforation failure of 20 # carbon steel in petrochemical system. It provides a theoretical basis for reasonably reducing corrosion failure in petrochemical industry. The innovation of this paper lies in: according to the actual operation condition of acid water pipeline, The correlation analysis of chemical process and the combination of numerical simulation and erosion corrosion experiment were carried out to construct the gas-liquid equilibrium environment of corrosive solution of acid water pipeline and to explore the test method and critical characteristic law of erosion corrosion characterization. The research results can provide theoretical support for petrochemical industry design optimization, equipment selection and failure analysis.
【学位授予单位】：浙江理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG178

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