离心压缩机叶轮应力腐蚀行为和机理的研究
发布时间：2018-07-15 11:31
【摘要】：离心式压缩机是一种以气体为工作介质的高速旋转叶轮机械,依靠叶轮高速旋转产生的离心力,使气体压力和速度都得到提高。依靠这一特性,离心式压缩机广泛应用于石油、化工、天然气输运、冶金、矿山等领域,是石油、化工等行业的关键设备。叶轮作为离心式压缩机的核心部件,工作环境具有高温、高压、高转速、工作介质种类繁多等特点,在其长期工作服役过程中,要承受离心载荷、工作介质的气动载荷、振动载荷、腐蚀介质的作用及颗粒杂质的冲击磨损,往往会产生各种损伤,如开裂、破断、减薄、变形等,这其中,应力和腐蚀环境共同导致的应力腐蚀破裂具有很强的隐蔽性和突然性,叶轮一旦发生应力腐蚀破裂,往往会导致重大安全事故的发生,因此,开展离心式压缩机叶轮应力腐蚀研究,掌握叶轮材料在实际服役环境中的应力腐蚀行为和机理,对于叶轮的设计和制造、保障企业安全生产和提高企业效益都有重要作用。本文依托国家重点基础研究发展计划(973计划)项目“再制造对象的多强场、跨尺度损伤行为与机理,可再制造的临界阈值(2011CB013401)”,模拟管道离心式压缩机叶轮实际服役环境,通过数值模拟方法、电化学方法、慢应变速率拉伸应力腐蚀试验法和恒位移预制裂纹应力腐蚀试验法,系统开展了叶轮钢FV520B及其焊接接头在高温、高压H2S/CO2环境中的应力腐蚀开裂(SCC)研究,得到如下研究成果：(1)采用数值模拟方法,分析了离心式压缩机叶轮内部流场对叶片应力场、温度场、速度场以及腐蚀介质分布的影响规律。流固耦合前后叶片等效应力分布趋势基本相同,最大值都位于叶片吸力面上,靠近前缘与轮盖的结合处。H2S在叶轮叶片吸力面、压力面靠近前轮盖处浓度较高,并且从叶轮入口至出口处,其质量分数逐渐增大。CO2由于分子质量更大,因此主要分布在叶片吸力面靠近后轮盖处以及压力面前部,并且从叶轮入口至出口含量逐步降低。叶片点蚀坑是叶片等效应力最大的位置,同时,流体速度在点蚀坑处急剧降低,造成H2S和CO2在点蚀坑处富集,进而成为应力腐蚀裂纹的起源处。(2)通过分析FV520B叶轮钢及其焊接接头在高温、高压H2S/CO2环境中的电化学极化曲线,研究了H2S浓度、C02浓度、温度、压力等环境参数对材料自腐蚀电位、腐蚀电流密度的影响规律,结果显示H2S在FV520B的电化学腐蚀过程中占主导地位,H2S的加入不但加速了FV520B叶轮钢的阳极溶解,对FV520B叶轮钢阴极反应也有很大的促进作用,随着H2S浓度的升高,FV520B自腐蚀电位降低,自腐蚀电流密度升高,腐蚀速率增加,当H2S摩尔百分比浓度高于12%时,FV520B自腐蚀电位开始趋于稳定。与母材相比,FV520B焊接接头在同样环境中的自腐蚀电位相对更负,自腐蚀电流密度更高,腐蚀速率更快。(3)FV520B叶轮钢在含H2S和C02环境中发生了明显的应力腐蚀破裂,应力腐蚀裂纹起源于材料表面,并向材料内部扩展,扩展方向垂直于应力方向,裂纹特征符合穿晶型应力腐蚀开裂特征,在试样侧面出现点蚀坑和细小裂纹,在应力的作用下逐渐扩展形成横向裂纹,试样断口微小裂纹明显增加,并且形成台阶状的二次裂纹扩展形貌,说明FV520B在含H2S和C02环境中的断裂形式为穿晶解理型脆性断裂,H2S对FV520B叶轮钢的应力腐蚀起主导作用,随H2S浓度的增加,材料力学性能不断降低,应力腐蚀敏感性指数上升。H2S浓度的升高可以加速FV520B阳极溶解反应,同时,大量的氢进入材料内部并在内部缺陷处富集,在外加载荷的作用下导致材料发生氢致开裂。因此,FV520B的应力腐蚀机理为阳极溶解和氢致开裂混合机制,裂纹扩展模式为穿晶型应力腐蚀开裂。(4)叶轮钢FV520B焊接接头在含H2S和C02环境中的抗应力腐蚀性能较差,H2S浓度变化对应力腐蚀敏感性影响较小,即使在H2S浓度很低的情况下,焊接接头的应力腐蚀倾向仍然非常严重。焊接工艺导致FV520B焊接接头内部存在大量的气孔和夹杂等缺陷,表面的缺陷会导致试样表面形成点蚀坑,进而发展为横向裂纹,内部的缺陷则会成为氢原子的聚积处,在氢压和应力的作用下形成孔洞,进而产生氢致开裂裂纹。由于焊接缺陷的存在,焊接接头试样断口凹凸不平,并且存在明显的台阶状二次裂纹,解理特征明显,体现了氢致开裂机制。温度对FV520B焊接接头在H2S/CO2环境中的应力腐蚀影响较大,FV520B焊接接头拉伸过程中自腐蚀电位变化规律与其应力腐蚀敏感性随温度变化规律相同,随着温度升高,自腐蚀电位升高,应力腐蚀敏感性降低。(5)通过对应力腐蚀敏感性指数的回归分析,建立FV520B及其焊接接头应力腐蚀敏感性指数与H2S含量、C02含量、温度和压力等实验介质参数之间的交互型数学模型,结果显示H2S浓度、温度对FV520B应力腐蚀敏感指数的影响较为显著,同时,温度分别与其它三个参数对应力腐蚀敏感指数产生交互作用。温度对FV520B焊接接头的应力腐蚀敏感指数影响最为显著,同时,CO2浓度与压力对其应力腐蚀敏感指数产生交互作用。(6)恒位移预制裂纹应力腐蚀试验显示,FV520B叶轮钢在H2S/CO2环境中的应力腐蚀裂纹扩展速率随加载应力强度因子的升高而逐渐增大,两者近似呈线性关系。随着H2S浓度的升高,导致材料发生应力腐蚀的临界应力强度因子KISCC随之下降,应力腐蚀裂纹扩展速率da/dt基本呈现增加的趋势,抗应力腐蚀性能变差。低初始加载应力强度因子情况下,随温度升高,KISCC先降低后升高,高初始加载应力强度因子情况下,KISCC基本呈现降低的趋势,当温度低于82℃时,应力腐蚀裂纹扩展速率随温度升高而降低,裂纹扩展速率与初始加载应力强度因子呈线性关系,当温度高于82℃时,应力腐蚀裂纹扩展速率随温度升高而增加,这与应力腐蚀敏感性研究结果相吻合。
[Abstract]:Centrifugal compressor is a kind of high speed rotating turbomachinery with gas as the working medium, which depends on the centrifugal force produced by the high speed rotation of the impeller to increase the pressure and speed of the gas. Depending on this characteristic, centrifugal compressor is widely used in oil, chemical, natural gas transportation, metallurgy, mine and other fields, which are the key of petroleum and chemical industry. As the core component of the centrifugal compressor, the impeller is the core component of the centrifugal compressor. The working environment has the characteristics of high temperature, high pressure, high speed and various kinds of working medium. During its long working service, the centrifugal load should be subjected to centrifugal load, the aerodynamic load of the working medium, the vibration load, the effect of corrosion medium and the impact wear of the particle impurity. The stress corrosion cracking, which is caused by stress and corrosion environment, has strong concealment and suddenness. Once the impeller occurs stress corrosion cracking, it often leads to the occurrence of major safety accidents. Therefore, the stress corrosion research of the open centrifugal compressor impeller is studied and the impeller material is mastered. The stress corrosion behavior and mechanism in the actual service environment play an important role in the design and manufacture of the impeller and the safety of the enterprise. This paper relies on the national key basic research development plan (973 Plan) project "the multi strength field of the remanufacturing object, the cross scale damage behavior and mechanism, the remanufacturing critical point." Threshold (2011CB013401) "is used to simulate the actual service environment of centrifugal compressor impeller. Through numerical simulation, electrochemical method, slow strain rate tensile stress corrosion test method and constant displacement prefabricated crack stress corrosion test method, the stress of the impeller steel FV520B and its welded joint in high temperature and high pressure H2S/CO2 environment are systematically carried out. The research results of corrosion cracking (SCC) are obtained as follows: (1) the influence of flow field on the blade stress field, temperature field, velocity field and corrosion medium distribution in centrifugal compressor impeller is analyzed by numerical simulation method. The equivalent stress distribution trend of the blade is basically the same before and after the fluid solid coupling, and the maximum value is located on the suction surface of the blade. .H2S, near the front edge and the wheel cover, is at the suction surface of the impeller blade. The pressure surface is close to the front wheel cover, and the mass fraction increases gradually from the inlet of the impeller to the exit, and the mass fraction increases as the molecular mass is larger, so the main distribution is near the rear wheel cover and the pressure front, and from the entrance of the impeller to the exit. The content of the blade pitting pit is the most important position of the equivalent stress of the blade. At the same time, the velocity of the fluid decreases sharply at the pitting pit, resulting in the enrichment of H2S and CO2 at the pitting pit, and then the origin of the stress corrosion crack. (2) the electrochemical polarization curve of the FV520B impeller steel and its welded joint in high temperature and high pressure H2S/CO2 environment is analyzed. The influence of H2S concentration, C02 concentration, temperature, pressure and other environmental parameters on the self corrosion potential and corrosion current density of the material is studied. The results show that H2S is dominant in the electrochemical corrosion process of FV520B. The addition of H2S not only accelerates the Yang Jirong solution of the FV520B impeller steel, but also promotes the cathode reaction of the FV520B impeller steel greatly. With the increase of H2S concentration, the self corrosion potential of FV520B decreased, corrosion current density increased and corrosion rate increased. When the molar percentage concentration of H2S was higher than 12%, FV520B self corrosion potential began to stabilize. Compared with the parent material, the self corrosion potential of FV520B welded joint in the same environment was more negative, corrosion current density was higher, rot was higher. The corrosion rate was faster. (3) the stress corrosion cracking occurred in the FV520B impeller steel in the environment of H2S and C02. The stress corrosion crack originated from the material surface and extended to the material. The direction of the crack was perpendicular to the stress direction. The crack characteristics conformed to the characteristic of the transgranular stress corrosion cracking and the pitting pit and small crack appeared on the side of the specimen. Under the action of force, the transverse crack is gradually expanded and the micro crack of the sample fracture increases obviously, and the step shape two crack growth morphology is formed. It shows that the fracture form of FV520B in the environment containing H2S and C02 is the brittle fracture of the transgranular cleavage type, and the H2S has the dominant effect on the stress corrosion of the FV520B impeller steel. With the increase of the H2S concentration, the material force is increased. The increase of the stress corrosion sensitivity index and the increase of.H2S concentration can accelerate the anodic dissolution reaction of FV520B. At the same time, a large number of hydrogen enters the material and enriching the internal defects and causes hydrogen cracking in the material under the effect of external loading. Therefore, the stress corrosion mechanism of FV520B is anodic dissolution and hydrogen induced cracking. The mode of crack propagation is transgranular stress corrosion cracking. (4) the resistance to stress corrosion of the FV520B welded joint in H2S and C02 environment is poor, and the change of H2S concentration is less affected by the stress corrosion sensitivity. The stress corrosion tendency of the welded joint is still very serious even when the H2S concentration is very low. The defects in the FV520B welding joint are caused by a large number of holes and inclusions. The defects of the surface will lead to the formation of the pitting pit on the surface of the specimen, and then to the transverse cracks. The internal defects will become the accumulation of hydrogen atoms. The holes are formed under the action of hydrogen pressure and stress. It is found that the fracture of the welded joint is uneven, and there is a clear step like two crack. The cleavage characteristic is obvious, which reflects the mechanism of hydrogen induced cracking. The temperature has great influence on the stress corrosion of the FV520B welded joint in the H2S/CO2 environment. The change of the self corrosion potential and the stress corrosion sensitivity of the FV520B welding joint during the tensile process The temperature change law is the same, as the temperature rises, the corrosion potential increases and the stress corrosion sensitivity decreases. (5) through the regression analysis of the stress corrosion sensitivity index, a mathematical model of the interaction between the stress corrosion sensitivity index of FV520B and its welded joint, H2S content, C02 content, temperature and pressure and other experimental medium parameters is established. The effect of temperature on the stress corrosion sensitivity index of FV520B is more significant. At the same time, the temperature has a interaction with the other three parameters corresponding to the stress corrosion sensitivity index of the other three parameters. The temperature has the most significant influence on the stress corrosion sensitivity index of the FV520B welded joint, while the CO2 concentration and pressure are produced by the stress corrosion sensitivity index. (6) the stress corrosion test of the constant displacement prefabricated crack shows that the stress corrosion crack growth rate of FV520B impeller steel increases with the increase of loading stress intensity factor in the H2S/CO2 environment, which is approximately linear. With the increase of H2S concentration, the critical stress intensity factor KISCC of the material is caused by stress corrosion. With the decrease of the stress corrosion crack growth rate da/dt, the resistance to stress corrosion is basically increased. Under the condition of low initial loading stress intensity factor, with the increase of temperature, the KISCC first decreases and then increases. Under the condition of high initial loading stress intensity factor, KISCC basically presents a decreasing trend, when the temperature is below 82 C, stress corrosion is found. The rate of crack propagation decreases with the increase of temperature, and the rate of crack growth is linear with the initial loading stress intensity factor. When the temperature is higher than 82, the rate of stress corrosion crack growth increases with the increase of temperature, which is in agreement with the results of the stress corrosion sensitivity study.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH452
，
本文编号：2123918
[Abstract]:Centrifugal compressor is a kind of high speed rotating turbomachinery with gas as the working medium, which depends on the centrifugal force produced by the high speed rotation of the impeller to increase the pressure and speed of the gas. Depending on this characteristic, centrifugal compressor is widely used in oil, chemical, natural gas transportation, metallurgy, mine and other fields, which are the key of petroleum and chemical industry. As the core component of the centrifugal compressor, the impeller is the core component of the centrifugal compressor. The working environment has the characteristics of high temperature, high pressure, high speed and various kinds of working medium. During its long working service, the centrifugal load should be subjected to centrifugal load, the aerodynamic load of the working medium, the vibration load, the effect of corrosion medium and the impact wear of the particle impurity. The stress corrosion cracking, which is caused by stress and corrosion environment, has strong concealment and suddenness. Once the impeller occurs stress corrosion cracking, it often leads to the occurrence of major safety accidents. Therefore, the stress corrosion research of the open centrifugal compressor impeller is studied and the impeller material is mastered. The stress corrosion behavior and mechanism in the actual service environment play an important role in the design and manufacture of the impeller and the safety of the enterprise. This paper relies on the national key basic research development plan (973 Plan) project "the multi strength field of the remanufacturing object, the cross scale damage behavior and mechanism, the remanufacturing critical point." Threshold (2011CB013401) "is used to simulate the actual service environment of centrifugal compressor impeller. Through numerical simulation, electrochemical method, slow strain rate tensile stress corrosion test method and constant displacement prefabricated crack stress corrosion test method, the stress of the impeller steel FV520B and its welded joint in high temperature and high pressure H2S/CO2 environment are systematically carried out. The research results of corrosion cracking (SCC) are obtained as follows: (1) the influence of flow field on the blade stress field, temperature field, velocity field and corrosion medium distribution in centrifugal compressor impeller is analyzed by numerical simulation method. The equivalent stress distribution trend of the blade is basically the same before and after the fluid solid coupling, and the maximum value is located on the suction surface of the blade. .H2S, near the front edge and the wheel cover, is at the suction surface of the impeller blade. The pressure surface is close to the front wheel cover, and the mass fraction increases gradually from the inlet of the impeller to the exit, and the mass fraction increases as the molecular mass is larger, so the main distribution is near the rear wheel cover and the pressure front, and from the entrance of the impeller to the exit. The content of the blade pitting pit is the most important position of the equivalent stress of the blade. At the same time, the velocity of the fluid decreases sharply at the pitting pit, resulting in the enrichment of H2S and CO2 at the pitting pit, and then the origin of the stress corrosion crack. (2) the electrochemical polarization curve of the FV520B impeller steel and its welded joint in high temperature and high pressure H2S/CO2 environment is analyzed. The influence of H2S concentration, C02 concentration, temperature, pressure and other environmental parameters on the self corrosion potential and corrosion current density of the material is studied. The results show that H2S is dominant in the electrochemical corrosion process of FV520B. The addition of H2S not only accelerates the Yang Jirong solution of the FV520B impeller steel, but also promotes the cathode reaction of the FV520B impeller steel greatly. With the increase of H2S concentration, the self corrosion potential of FV520B decreased, corrosion current density increased and corrosion rate increased. When the molar percentage concentration of H2S was higher than 12%, FV520B self corrosion potential began to stabilize. Compared with the parent material, the self corrosion potential of FV520B welded joint in the same environment was more negative, corrosion current density was higher, rot was higher. The corrosion rate was faster. (3) the stress corrosion cracking occurred in the FV520B impeller steel in the environment of H2S and C02. The stress corrosion crack originated from the material surface and extended to the material. The direction of the crack was perpendicular to the stress direction. The crack characteristics conformed to the characteristic of the transgranular stress corrosion cracking and the pitting pit and small crack appeared on the side of the specimen. Under the action of force, the transverse crack is gradually expanded and the micro crack of the sample fracture increases obviously, and the step shape two crack growth morphology is formed. It shows that the fracture form of FV520B in the environment containing H2S and C02 is the brittle fracture of the transgranular cleavage type, and the H2S has the dominant effect on the stress corrosion of the FV520B impeller steel. With the increase of the H2S concentration, the material force is increased. The increase of the stress corrosion sensitivity index and the increase of.H2S concentration can accelerate the anodic dissolution reaction of FV520B. At the same time, a large number of hydrogen enters the material and enriching the internal defects and causes hydrogen cracking in the material under the effect of external loading. Therefore, the stress corrosion mechanism of FV520B is anodic dissolution and hydrogen induced cracking. The mode of crack propagation is transgranular stress corrosion cracking. (4) the resistance to stress corrosion of the FV520B welded joint in H2S and C02 environment is poor, and the change of H2S concentration is less affected by the stress corrosion sensitivity. The stress corrosion tendency of the welded joint is still very serious even when the H2S concentration is very low. The defects in the FV520B welding joint are caused by a large number of holes and inclusions. The defects of the surface will lead to the formation of the pitting pit on the surface of the specimen, and then to the transverse cracks. The internal defects will become the accumulation of hydrogen atoms. The holes are formed under the action of hydrogen pressure and stress. It is found that the fracture of the welded joint is uneven, and there is a clear step like two crack. The cleavage characteristic is obvious, which reflects the mechanism of hydrogen induced cracking. The temperature has great influence on the stress corrosion of the FV520B welded joint in the H2S/CO2 environment. The change of the self corrosion potential and the stress corrosion sensitivity of the FV520B welding joint during the tensile process The temperature change law is the same, as the temperature rises, the corrosion potential increases and the stress corrosion sensitivity decreases. (5) through the regression analysis of the stress corrosion sensitivity index, a mathematical model of the interaction between the stress corrosion sensitivity index of FV520B and its welded joint, H2S content, C02 content, temperature and pressure and other experimental medium parameters is established. The effect of temperature on the stress corrosion sensitivity index of FV520B is more significant. At the same time, the temperature has a interaction with the other three parameters corresponding to the stress corrosion sensitivity index of the other three parameters. The temperature has the most significant influence on the stress corrosion sensitivity index of the FV520B welded joint, while the CO2 concentration and pressure are produced by the stress corrosion sensitivity index. (6) the stress corrosion test of the constant displacement prefabricated crack shows that the stress corrosion crack growth rate of FV520B impeller steel increases with the increase of loading stress intensity factor in the H2S/CO2 environment, which is approximately linear. With the increase of H2S concentration, the critical stress intensity factor KISCC of the material is caused by stress corrosion. With the decrease of the stress corrosion crack growth rate da/dt, the resistance to stress corrosion is basically increased. Under the condition of low initial loading stress intensity factor, with the increase of temperature, the KISCC first decreases and then increases. Under the condition of high initial loading stress intensity factor, KISCC basically presents a decreasing trend, when the temperature is below 82 C, stress corrosion is found. The rate of crack propagation decreases with the increase of temperature, and the rate of crack growth is linear with the initial loading stress intensity factor. When the temperature is higher than 82, the rate of stress corrosion crack growth increases with the increase of temperature, which is in agreement with the results of the stress corrosion sensitivity study.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH452
，
本文编号：2123918
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