基于有限元模拟分析重沸器管束失效行为
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摘要
目的针对某重沸器在生产过程中发生的管束泄漏问题,开展失效行为及原因分析,为此类重沸器的失效控制提供理论依据。方法基于此类管束的服役工况和生产标准,通过化学成分分析、金相组织检验、腐蚀产物分析等理化检验,以及有限元数值模拟的方法,综合分析重沸器管束材料性能、腐蚀机理和温度场及流场的特征。结果该重沸器管束理化检验结果表明,其化学成分符合相关标准的要求,金相组织未见异常,其外壁穿孔处堆积了一层疏松的腐蚀产物,其化学成分组成为C、O、S、Fe和少量Cl,物相组成为Fe_3O_4、Fe_2O_3、FeCO_3和CaSO_4。流场有限元模拟结果表明,壳程凝析油的流速整体较低,存在流体滞留现象(约1.5×10-4 m/s)。温度场有限元模拟结果表明,壳程存在一处局部高温区(约105～112℃)。结论该重沸器管束失效行为是在局部高温区和流体滞留区的管束外壁发生严重的CO2局部腐蚀,较高含量的Cl-穿透FeCO_3腐蚀产物膜促进点蚀而进一步加剧了管束腐蚀的进程,进而导致管束发生外腐蚀穿孔泄漏。
The work aims to analyze the failure behavior and cause for the leaking problems of tube bundle during the production process of reboiler and then provide theoretical basis for the failure control of such reboiler. Based on production standards and service conditions of the faulty tube bundle, material properties, corrosion mechanism and flow and temperature distribution characteristics were analyzed through chemical composition analysis, metallographic structure analysis, corrosion products analysis and finite element analysis. From the physiochemical test results, the chemical composition of tube bundle was in conformity with relevant standards, and no abnormality was detected in metallographic structure. However, a layer of loose corrosion products was accumulated at the perforated outer wall and the chemical elements included C, O, S, Fe, and a small amount of Cl. Besides, the main phase compositions were Fe_3O_4, Fe_2O_3, FeCO_3 and CaSO_4. Based on the result of finite element simulation of flow distribution, the flow rate of condensate oil in shell side was generally low and there was fluid retention phenomenon(about 1.5×10~(-4) m/s). In addition, a local high-temperature zone(about 105～112 ℃) on the shell side was found according to finite element simulation of temperature distribution. The failure behavior of the reboiler tube bundle is serious local CO_2 corrosion caused to the outer wall of tube bundle in local high-temperature and fluid retention areas. The Cl- with high concentration penetrates corrosion product film(FeCO_3) and promotes pitting corrosion, thus ultimately leading to external corrosion perforation and leaking problem.
The work aims to analyze the failure behavior and cause for the leaking problems of tube bundle during the production process of reboiler and then provide theoretical basis for the failure control of such reboiler. Based on production standards and service conditions of the faulty tube bundle, material properties, corrosion mechanism and flow and temperature distribution characteristics were analyzed through chemical composition analysis, metallographic structure analysis, corrosion products analysis and finite element analysis. From the physiochemical test results, the chemical composition of tube bundle was in conformity with relevant standards, and no abnormality was detected in metallographic structure. However, a layer of loose corrosion products was accumulated at the perforated outer wall and the chemical elements included C, O, S, Fe, and a small amount of Cl. Besides, the main phase compositions were Fe_3O_4, Fe_2O_3, FeCO_3 and CaSO_4. Based on the result of finite element simulation of flow distribution, the flow rate of condensate oil in shell side was generally low and there was fluid retention phenomenon(about 1.5×10~(-4) m/s). In addition, a local high-temperature zone(about 105～112 ℃) on the shell side was found according to finite element simulation of temperature distribution. The failure behavior of the reboiler tube bundle is serious local CO_2 corrosion caused to the outer wall of tube bundle in local high-temperature and fluid retention areas. The Cl- with high concentration penetrates corrosion product film(FeCO_3) and promotes pitting corrosion, thus ultimately leading to external corrosion perforation and leaking problem.
引文
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[16]陈长风,路民旭,赵国仙,等.温度?Cl-浓度?Cr元素对N80钢CO2腐蚀电极过程的影响[J].金属学报,2003,39(8):848-854.CHEN Chang-feng,LU Min-xu,ZHAO Guo-xian,et al.Effects of temperature,Cl-concentration and Cr on electrode reactions of CO2 corrosion of N80 steel[J].Acta metallurgica sinica,2003,39(8):848-854.
[2]李磊,邝献任,姬蕊,等.某油田316L/L360NB机械式双金属复合管失效行为及原因分析[J].表面技术,2018,47(6):224-231.LI Lei,KUANG Xian-ren,JI Rui,et al.Analysis on failure behavior and reason of 316L/L360NB mechanically bimetallic composite pipes used in an oilfield[J].Surface technology,2018,47(6):224-231.
[3]路民旭,白真权,赵新伟,等.油气采集输运中的腐蚀现状及典型案例[J].腐蚀与防护,2002,23(3):105-116.LU Min-xu,BAI Zhen-quan,ZHAO Xin-wei,et al.Actuality and typical cases for corrosion in the process of extraction,gathering,storage and transmission for oil and gas[J].Corrosion&protection,2002,23(3):105-116.
[4]卜英南,陈祥彬,张莹莹,等.折流板结构对换热器壳程流动和传热性能的影响[J].辽宁石油化工大学学报,2018,38(5):72-76.BU Ying-nan,CHEN Xiang-bin,ZHANG Ying-ying,et al.Shell-side fluid flow and heat transfer in curved baffle heat exchanger[J].Journal of Liaoning Shihua University,2018,38(5):72-76.
[5]王为良.管壳式换热器壳侧流场数值模拟[D].北京:中国石油大学,2010:2-6.WANG Wei-liang.Numerical simulation of shell-side fluid-flow in the shell-and-tube heat exchanger[D].Beijing:China University of Petroleum,2010:2-6.
[6]付磊,曾燚林,唐克伦,等.管壳式换热器壳程流体流动与传热数值模拟[J].压力容器,2012,29(5):36-41.FU Lei,ZENG Yan-lin,TANG Ke-lun,et al.Numerical simulation study of shell-side fluid flow and heat transfer in shell-and-tube heat exchanger[J].Pressure vessel,2012,29(5):36-41.
[7]王秋灵.再生塔底重沸器的腐蚀和对策[J].腐蚀与防护,2004(10):432-433.WANG Qiu-ling.Corrosion and counter measures of reboiler in regenerator[J].Corrosion&protection,2004(10):432-433.
[8]HAN C,ZOU L.Study on the heat transfer characteristics of a moderate-temperature heat pipe heat exchanger[J].International journal of heat&mass transfer,2015,91:302-310.
[9]DIAO Y,ZHANG J,ZHAO W Y Y.Experimental study on the heat recovery characteristic of a plate heat pipe heat exchanger in room ventilation[J].HVAC&R research,2014,20(7):828-835.
[10]LAUBSCHER R,DOBSON R T.Theoretical and experimental modelling of a heat pipe heat exchanger for high temperature nuclear reactor technology[J].Applied thermal engineering,2013,61(2):259-267.
[11]YONG G L,YA L H,RUI L,et al.Effects of baffle inclination angle on flow and heat transfer of a heat exchanger with helical baffles[J].Chemical engineering and processing,2008(47):2336-2345.
[12]LAUNDER B E,SPALDING D B.Lectures in mathematical models of turbulence[M].London:Academic Press,1972:355-392.
[13]王春泉.雅克拉气田集输管材的CO2腐蚀研究[D].北京:中国石油大学,2009:7-8WANG Chun-quan.Study on the CO2 corrosion of the gathering pipeline for gas in Yakela gas field[D].Beijing:China University of Petroleum,2009:7-8
[14]张学元,王凤平,陈卓元,等.油气开发中二氧化碳腐蚀的研究现状和趋势[J].油田化学,1997(2):95-101.ZHANG Xue-yuan,WANG Feng-ping,CHEN Zhuo-yuan,et al.A review on carbon dioxide corrosion of steel in aqueous media for oilfield chemical engineers[J].Oilfield chemistry,1997(2):95-101.
[15]肖雯雯,宋成立,白真权,等.油田地面集输管道腐蚀穿孔风险分析[J].油气田地面工程,2017,36(4):81-85.XIAO Wen-wen,SONG Cheng-li,BAI Zhen-quan,et al.Risk analysis on surface gathering pipeline corrosion in oil fields[J].Oil-gas field surface engineering,2017,36(4):81-85.
[16]陈长风,路民旭,赵国仙,等.温度?Cl-浓度?Cr元素对N80钢CO2腐蚀电极过程的影响[J].金属学报,2003,39(8):848-854.CHEN Chang-feng,LU Min-xu,ZHAO Guo-xian,et al.Effects of temperature,Cl-concentration and Cr on electrode reactions of CO2 corrosion of N80 steel[J].Acta metallurgica sinica,2003,39(8):848-854.
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