離心壓縮機(jī)葉輪應(yīng)力腐蝕行為和機(jī)理的研究
發(fā)布時(shí)間：2018-07-15 11:31
【摘要】：離心式壓縮機(jī)是一種以氣體為工作介質(zhì)的高速旋轉(zhuǎn)葉輪機(jī)械,依靠葉輪高速旋轉(zhuǎn)產(chǎn)生的離心力,使氣體壓力和速度都得到提高。依靠這一特性,離心式壓縮機(jī)廣泛應(yīng)用于石油、化工、天然氣輸運(yùn)、冶金、礦山等領(lǐng)域,是石油、化工等行業(yè)的關(guān)鍵設(shè)備。葉輪作為離心式壓縮機(jī)的核心部件,工作環(huán)境具有高溫、高壓、高轉(zhuǎn)速、工作介質(zhì)種類繁多等特點(diǎn),在其長期工作服役過程中,要承受離心載荷、工作介質(zhì)的氣動(dòng)載荷、振動(dòng)載荷、腐蝕介質(zhì)的作用及顆粒雜質(zhì)的沖擊磨損,往往會(huì)產(chǎn)生各種損傷,如開裂、破斷、減薄、變形等,這其中,應(yīng)力和腐蝕環(huán)境共同導(dǎo)致的應(yīng)力腐蝕破裂具有很強(qiáng)的隱蔽性和突然性,葉輪一旦發(fā)生應(yīng)力腐蝕破裂,往往會(huì)導(dǎo)致重大安全事故的發(fā)生,因此,開展離心式壓縮機(jī)葉輪應(yīng)力腐蝕研究,掌握葉輪材料在實(shí)際服役環(huán)境中的應(yīng)力腐蝕行為和機(jī)理,對于葉輪的設(shè)計(jì)和制造、保障企業(yè)安全生產(chǎn)和提高企業(yè)效益都有重要作用。本文依托國家重點(diǎn)基礎(chǔ)研究發(fā)展計(jì)劃(973計(jì)劃)項(xiàng)目“再制造對象的多強(qiáng)場、跨尺度損傷行為與機(jī)理,可再制造的臨界閾值(2011CB013401)”,模擬管道離心式壓縮機(jī)葉輪實(shí)際服役環(huán)境,通過數(shù)值模擬方法、電化學(xué)方法、慢應(yīng)變速率拉伸應(yīng)力腐蝕試驗(yàn)法和恒位移預(yù)制裂紋應(yīng)力腐蝕試驗(yàn)法,系統(tǒng)開展了葉輪鋼FV520B及其焊接接頭在高溫、高壓H2S/CO2環(huán)境中的應(yīng)力腐蝕開裂(SCC)研究,得到如下研究成果：(1)采用數(shù)值模擬方法,分析了離心式壓縮機(jī)葉輪內(nèi)部流場對葉片應(yīng)力場、溫度場、速度場以及腐蝕介質(zhì)分布的影響規(guī)律。流固耦合前后葉片等效應(yīng)力分布趨勢基本相同,最大值都位于葉片吸力面上,靠近前緣與輪蓋的結(jié)合處。H2S在葉輪葉片吸力面、壓力面靠近前輪蓋處濃度較高,并且從葉輪入口至出口處,其質(zhì)量分?jǐn)?shù)逐漸增大。CO2由于分子質(zhì)量更大,因此主要分布在葉片吸力面靠近后輪蓋處以及壓力面前部,并且從葉輪入口至出口含量逐步降低。葉片點(diǎn)蝕坑是葉片等效應(yīng)力最大的位置,同時(shí),流體速度在點(diǎn)蝕坑處急劇降低,造成H2S和CO2在點(diǎn)蝕坑處富集,進(jìn)而成為應(yīng)力腐蝕裂紋的起源處。(2)通過分析FV520B葉輪鋼及其焊接接頭在高溫、高壓H2S/CO2環(huán)境中的電化學(xué)極化曲線,研究了H2S濃度、C02濃度、溫度、壓力等環(huán)境參數(shù)對材料自腐蝕電位、腐蝕電流密度的影響規(guī)律,結(jié)果顯示H2S在FV520B的電化學(xué)腐蝕過程中占主導(dǎo)地位,H2S的加入不但加速了FV520B葉輪鋼的陽極溶解,對FV520B葉輪鋼陰極反應(yīng)也有很大的促進(jìn)作用,隨著H2S濃度的升高,FV520B自腐蝕電位降低,自腐蝕電流密度升高,腐蝕速率增加,當(dāng)H2S摩爾百分比濃度高于12%時(shí),FV520B自腐蝕電位開始趨于穩(wěn)定。與母材相比,FV520B焊接接頭在同樣環(huán)境中的自腐蝕電位相對更負(fù),自腐蝕電流密度更高,腐蝕速率更快。(3)FV520B葉輪鋼在含H2S和C02環(huán)境中發(fā)生了明顯的應(yīng)力腐蝕破裂,應(yīng)力腐蝕裂紋起源于材料表面,并向材料內(nèi)部擴(kuò)展,擴(kuò)展方向垂直于應(yīng)力方向,裂紋特征符合穿晶型應(yīng)力腐蝕開裂特征,在試樣側(cè)面出現(xiàn)點(diǎn)蝕坑和細(xì)小裂紋,在應(yīng)力的作用下逐漸擴(kuò)展形成橫向裂紋,試樣斷口微小裂紋明顯增加,并且形成臺(tái)階狀的二次裂紋擴(kuò)展形貌,說明FV520B在含H2S和C02環(huán)境中的斷裂形式為穿晶解理型脆性斷裂,H2S對FV520B葉輪鋼的應(yīng)力腐蝕起主導(dǎo)作用,隨H2S濃度的增加,材料力學(xué)性能不斷降低,應(yīng)力腐蝕敏感性指數(shù)上升。H2S濃度的升高可以加速FV520B陽極溶解反應(yīng),同時(shí),大量的氫進(jìn)入材料內(nèi)部并在內(nèi)部缺陷處富集,在外加載荷的作用下導(dǎo)致材料發(fā)生氫致開裂。因此,FV520B的應(yīng)力腐蝕機(jī)理為陽極溶解和氫致開裂混合機(jī)制,裂紋擴(kuò)展模式為穿晶型應(yīng)力腐蝕開裂。(4)葉輪鋼FV520B焊接接頭在含H2S和C02環(huán)境中的抗應(yīng)力腐蝕性能較差,H2S濃度變化對應(yīng)力腐蝕敏感性影響較小,即使在H2S濃度很低的情況下,焊接接頭的應(yīng)力腐蝕傾向仍然非常嚴(yán)重。焊接工藝導(dǎo)致FV520B焊接接頭內(nèi)部存在大量的氣孔和夾雜等缺陷,表面的缺陷會(huì)導(dǎo)致試樣表面形成點(diǎn)蝕坑,進(jìn)而發(fā)展為橫向裂紋,內(nèi)部的缺陷則會(huì)成為氫原子的聚積處,在氫壓和應(yīng)力的作用下形成孔洞,進(jìn)而產(chǎn)生氫致開裂裂紋。由于焊接缺陷的存在,焊接接頭試樣斷口凹凸不平,并且存在明顯的臺(tái)階狀二次裂紋,解理特征明顯,體現(xiàn)了氫致開裂機(jī)制。溫度對FV520B焊接接頭在H2S/CO2環(huán)境中的應(yīng)力腐蝕影響較大,FV520B焊接接頭拉伸過程中自腐蝕電位變化規(guī)律與其應(yīng)力腐蝕敏感性隨溫度變化規(guī)律相同,隨著溫度升高,自腐蝕電位升高,應(yīng)力腐蝕敏感性降低。(5)通過對應(yīng)力腐蝕敏感性指數(shù)的回歸分析,建立FV520B及其焊接接頭應(yīng)力腐蝕敏感性指數(shù)與H2S含量、C02含量、溫度和壓力等實(shí)驗(yàn)介質(zhì)參數(shù)之間的交互型數(shù)學(xué)模型,結(jié)果顯示H2S濃度、溫度對FV520B應(yīng)力腐蝕敏感指數(shù)的影響較為顯著,同時(shí),溫度分別與其它三個(gè)參數(shù)對應(yīng)力腐蝕敏感指數(shù)產(chǎn)生交互作用。溫度對FV520B焊接接頭的應(yīng)力腐蝕敏感指數(shù)影響最為顯著,同時(shí),CO2濃度與壓力對其應(yīng)力腐蝕敏感指數(shù)產(chǎn)生交互作用。(6)恒位移預(yù)制裂紋應(yīng)力腐蝕試驗(yàn)顯示,FV520B葉輪鋼在H2S/CO2環(huán)境中的應(yīng)力腐蝕裂紋擴(kuò)展速率隨加載應(yīng)力強(qiáng)度因子的升高而逐漸增大,兩者近似呈線性關(guān)系。隨著H2S濃度的升高,導(dǎo)致材料發(fā)生應(yīng)力腐蝕的臨界應(yīng)力強(qiáng)度因子KISCC隨之下降,應(yīng)力腐蝕裂紋擴(kuò)展速率da/dt基本呈現(xiàn)增加的趨勢,抗應(yīng)力腐蝕性能變差。低初始加載應(yīng)力強(qiáng)度因子情況下,隨溫度升高,KISCC先降低后升高,高初始加載應(yīng)力強(qiáng)度因子情況下,KISCC基本呈現(xiàn)降低的趨勢,當(dāng)溫度低于82℃時(shí),應(yīng)力腐蝕裂紋擴(kuò)展速率隨溫度升高而降低,裂紋擴(kuò)展速率與初始加載應(yīng)力強(qiáng)度因子呈線性關(guān)系,當(dāng)溫度高于82℃時(shí),應(yīng)力腐蝕裂紋擴(kuò)展速率隨溫度升高而增加,這與應(yīng)力腐蝕敏感性研究結(jié)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.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TH452
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本文編號：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.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TH452
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本文編號：2123918
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