减顶水冷器腐蚀失效分析及材质腐蚀规律研究
发布时间：2018-11-15 23:24
【摘要】：常减压装置的腐蚀问题一直是困扰炼化企业的一个重点难题,腐蚀风险的存在直接影响炼油装置的长周期运行,安全加工生产、产品质量以及企业经济效益。探究腐蚀机理及腐蚀发生原因,有针对性的解决常减压装置的腐蚀问题,对于企业安全高效生产具有非常重要的实际意义。因此,本文做了以下几方面研究：(1)本文通过金相显微镜和扫描电镜对换热器支撑梁和管束裂纹及孔蚀形貌进行表征,并通过电子能谱和洛氏硬度仪对支撑梁失效件、腐蚀产物进行了电子能谱扫描和材质硬度检测,分析了减顶水冷换热器腐蚀开裂原因,确定换热器换热管的腐蚀失效主要以点蚀为主,而支撑梁主要腐蚀失效形式为点蚀加开裂失效。对换热器材质进行分析,结果表明：换热管材质成分基本符合304材质特征,在HC1-H2S-H2O酸性环境下仅发生了点蚀,但是支撑梁成分检测结果显示Ni、Cr元素含量均偏低,趋于标准含量线以下;支撑梁材质硬度检测结果为32 HRC,超过设备设计要求22 HRC；金相特征观察显示,支撑梁裂纹呈台阶状分布,并且沿晶开裂；腐蚀产物成分分析,检测出含有Cl元素和S元素。综合以上分析得出结论：炼油厂所炼原油复杂多变,电脱盐设备脱盐效果不稳定,导致减压塔顶HCl、H2S含量升高,遇到冷凝水形成HCl-H2S-H2O酸性环境,导致设备支撑梁出现“台阶状”沿晶开裂,即典型的氢脆失效特征。支撑梁由于固溶不好或者未进行固溶处理导致硬度较高,高硬度的材质在HCl-H2S-H2O环境下容易诱发氢致开裂。(2)对2205双相不锈钢腐蚀规律做了详细研究,主要考虑氯离子和硫离子两种因素对2205双相钢腐蚀规律的影响。通过对2205双相钢孔蚀温度曲线的一系列测试,得出氯离子浓度越高,2205双相钢的孔蚀温度越低,同时考察pH值影响因素,pH值越低,2205双相钢的孔蚀温度也相应越低。通过对2205双相钢交流阻抗曲线测试,结果表明,硫离子的存在影响了钝化膜的自我修复生长过程,使得2205双相不锈钢的钝化膜更容易受到氯离子侵蚀破坏,而且硫离子浓度越高,这种破坏作用越明显。同时也考察了pH值和温度的影响因素,在酸性条件下,硫离子的作用更加强烈,高温环境下,硫离子也显出了很高的活性,更加促进氯离子的腐蚀作用。这一系列规律对于常减压塔顶相应温度下,如何控制氯离子浓度和硫离子浓度以及pH值范围等参数,降低设备腐蚀风险具有实际的指导意义。以上相关腐蚀规律的研究对提高常减压系统装置的可靠性、延长设备安全运行周期、确保企业的生产安全及经济效益具有一定的指导意义和应用价值。
[Abstract]:The corrosion problem of atmospheric and vacuum plant has been a key problem for refinery and chemical enterprises. The existence of corrosion risk directly affects the long period operation, safe processing and production, product quality and economic benefit of the refinery plant. It is of great practical significance to probe into the corrosion mechanism and the causes of corrosion and to solve the corrosion problem of atmospheric and vacuum equipment for the safe and efficient production of enterprises. Therefore, the following aspects have been studied in this paper: (1) the crack and pitting morphology of the support beam and tube bundle of heat exchanger are characterized by metallographic microscope and scanning electron microscope, and the failure parts of the support beam are analyzed by EDS and Rockwell hardness instrument. The corrosion products were scanned by EDS and the hardness of the material was tested. The reason of corrosion cracking in the top water cooling heat exchanger was analyzed. It was determined that the corrosion failure of heat exchanger tube was mainly pitting corrosion. The main corrosion failure form of support beam is pitting plus cracking failure. The material of heat exchanger is analyzed. The results show that the material composition of heat exchanger pipe basically accords with the material characteristic of 304, and only pitting corrosion occurs in the acidic environment of HC1-H2S-H2O, but the testing results of the component of support beam show that the content of Ni,Cr element is on the low side. Tend below the standard content line; Hardness test of support beam material is 32 HRC, exceeding design requirement of equipment 22 HRC; Metallographic observation shows that the crack of the supporting beam is a step shape and intergranular crack, and the corrosion product is found to contain Cl and S elements by analyzing the composition of the corrosion product. By synthesizing the above analysis, it is concluded that the crude oil refined in the refinery is complex and changeable, and the desalination effect of the electric desalting equipment is unstable, which leads to the increase of the HCl,H2S content at the top of the decompression tower and the formation of acidic HCl-H2S-H2O environment by condensing water. Leading to the "step" intergranular cracking of the support beam, that is, typical hydrogen embrittlement failure characteristics. The hardness of the support beam is high due to poor solution or no solution treatment, and the high hardness material can easily induce hydrogen induced cracking in HCl-H2S-H2O environment. (2) the corrosion law of 2205 duplex stainless steel is studied in detail. The influence of chloride ion and sulfur ion on corrosion law of 2205 duplex steel was considered. Through a series of tests on the pitting corrosion temperature curve of 2205 dual phase steel, it is concluded that the higher the chloride ion concentration, the lower the pitting corrosion temperature of 2205 dual phase steel. At the same time, the influence factors of pH value are investigated. The lower the pH value, the lower the pitting corrosion temperature of 2205 dual phase steel. By measuring the AC impedance curves of 2205 duplex steel, the results show that the existence of sulfur ions affects the self-repair growth process of the passivation film and makes the passivation film of 2205 duplex stainless steel more vulnerable to chloride erosion. Moreover, the higher the concentration of sulfur ion, the more obvious the destructive effect is. At the same time, the influence factors of pH value and temperature were also investigated. The effect of sulfur ion was more intense under acidic condition, and the sulfur ion also showed high activity in high temperature environment, and promoted the corrosion of chloride ion more. This series of rules has practical guiding significance for how to control the concentration of chloride ion and sulfur ion and the range of pH value at the corresponding temperature of the top of atmospheric and vacuum tower, and to reduce the corrosion risk of equipment. The above research on corrosion law has certain guiding significance and application value for improving the reliability of atmospheric and vacuum system equipment, prolonging the safe operation period of equipment and ensuring the production safety and economic benefit of the enterprise.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ051.5
本文编号：2334708
[Abstract]:The corrosion problem of atmospheric and vacuum plant has been a key problem for refinery and chemical enterprises. The existence of corrosion risk directly affects the long period operation, safe processing and production, product quality and economic benefit of the refinery plant. It is of great practical significance to probe into the corrosion mechanism and the causes of corrosion and to solve the corrosion problem of atmospheric and vacuum equipment for the safe and efficient production of enterprises. Therefore, the following aspects have been studied in this paper: (1) the crack and pitting morphology of the support beam and tube bundle of heat exchanger are characterized by metallographic microscope and scanning electron microscope, and the failure parts of the support beam are analyzed by EDS and Rockwell hardness instrument. The corrosion products were scanned by EDS and the hardness of the material was tested. The reason of corrosion cracking in the top water cooling heat exchanger was analyzed. It was determined that the corrosion failure of heat exchanger tube was mainly pitting corrosion. The main corrosion failure form of support beam is pitting plus cracking failure. The material of heat exchanger is analyzed. The results show that the material composition of heat exchanger pipe basically accords with the material characteristic of 304, and only pitting corrosion occurs in the acidic environment of HC1-H2S-H2O, but the testing results of the component of support beam show that the content of Ni,Cr element is on the low side. Tend below the standard content line; Hardness test of support beam material is 32 HRC, exceeding design requirement of equipment 22 HRC; Metallographic observation shows that the crack of the supporting beam is a step shape and intergranular crack, and the corrosion product is found to contain Cl and S elements by analyzing the composition of the corrosion product. By synthesizing the above analysis, it is concluded that the crude oil refined in the refinery is complex and changeable, and the desalination effect of the electric desalting equipment is unstable, which leads to the increase of the HCl,H2S content at the top of the decompression tower and the formation of acidic HCl-H2S-H2O environment by condensing water. Leading to the "step" intergranular cracking of the support beam, that is, typical hydrogen embrittlement failure characteristics. The hardness of the support beam is high due to poor solution or no solution treatment, and the high hardness material can easily induce hydrogen induced cracking in HCl-H2S-H2O environment. (2) the corrosion law of 2205 duplex stainless steel is studied in detail. The influence of chloride ion and sulfur ion on corrosion law of 2205 duplex steel was considered. Through a series of tests on the pitting corrosion temperature curve of 2205 dual phase steel, it is concluded that the higher the chloride ion concentration, the lower the pitting corrosion temperature of 2205 dual phase steel. At the same time, the influence factors of pH value are investigated. The lower the pH value, the lower the pitting corrosion temperature of 2205 dual phase steel. By measuring the AC impedance curves of 2205 duplex steel, the results show that the existence of sulfur ions affects the self-repair growth process of the passivation film and makes the passivation film of 2205 duplex stainless steel more vulnerable to chloride erosion. Moreover, the higher the concentration of sulfur ion, the more obvious the destructive effect is. At the same time, the influence factors of pH value and temperature were also investigated. The effect of sulfur ion was more intense under acidic condition, and the sulfur ion also showed high activity in high temperature environment, and promoted the corrosion of chloride ion more. This series of rules has practical guiding significance for how to control the concentration of chloride ion and sulfur ion and the range of pH value at the corresponding temperature of the top of atmospheric and vacuum tower, and to reduce the corrosion risk of equipment. The above research on corrosion law has certain guiding significance and application value for improving the reliability of atmospheric and vacuum system equipment, prolonging the safe operation period of equipment and ensuring the production safety and economic benefit of the enterprise.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ051.5
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