S-M. Hu et al/Case Studies in Engineering Failure Analysis 3(2015)52-61 4. Conclusions 1. The material of heat exchange tubes in ammonia evaporators is confirmed to be 10 carbon steel and all testified to be qualified to requirements 2. The connection between tubes and tubesheet is seal welding but without physical expansion. As a result, the welded joints are prone to cracking when subject to fluctuation of operating conditions. 3. Heat-exchange tubes in ammonia evaporators exhibit serious corroded defects and localized tube wall has thinned badly. The failure concretely happened as following steps: irstly, the heat-exchange tubes suffered uniform corrosion and pitting in humid environment with presence of Cl, sand CO2. Besides, the interaction behavior of them accelerated material degradation process in weak sites, bringing about serious localized wall thinning of tubes. Then affected by temperature fluctuation and slight me sion, corrosion layers gradually got cracking and some micro cracking initiated right from the pits. with its ion, corrosion layer subsequently split into small pieces and scaled off the surface. As a result, the tube wall co thinned, leading to premature failure of ammonia evaporators in the end. 5. Prevention measures 1. The tube ends should be seal welding to tubesheet with physical expansion so as to increase their reliabilities. 2. Strictly control the contents of chloride ions and water vapor in ammonia evaporators introduced by equipment upstream to avoid pitting on the heat exchange tubes caused by chloride ions 3. Clean up the corrosion products on the tubes during shutdown maintenance of evaporators in case of under-deposit corrosion References 12 Jahromi SAL, AliPour MM, Beirami A Failu is of 101-C ammonia plant heat exchange. Eng Fail Anal 2003: 10(4): 405-21 Abbasfard H, Ghanbari M, Ghasemi A, ghad sajani HH, Ali Moradi A Failure analysis and modeling of super heater tubes of a waste heat boiler ermally coupled in ammonia oxidation Eng Fail Ana2012:26:285-92. [3] Bhaumik SK. Ramgaraju R, Parameswara MA, Bhaskaran TA Venkataswamy A, Raghuram AC, et al. Failure of reformer tube of an ammonia plant. Eng il Anal2002:95):553-61 Arevalo A, Esparza P, Gomis Bas C, Morales J. Gonzalez S, de Sanchez SR Corrosion on steam-side heat exchange tubes. Mater Perform 1996: 35(1): 67-8. Ueda S Onishi H, Okubo M, Takegawa T. Corrosion of am ant heat exchanger. Ammonia Plant Saf Relat Facil 1978: 20: 98-102. [8] Li Al. Wang wQ, Wang XM, Zhao D Fatigue and brittle fracture of carbon steel process pipeline. Eng Fail Anal 2005: 12: 527-36. Yang ZG, Gong Y, Yuan JZ Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part I: Electrochemical corrosion. Mater Corros 2012: 63(1): 7-17. [11] Gong Y, Yang ZG. Failure analysis of one peculiar"Yin-Yang corrosion morphology on heat exchanger tubes in purified terephthalic acid (PTA)dryer. g Fail Anal2013:31:203- [12] Gong Y, Yang C, Yao C, Yang ZG. Acidic/caustic alternating corrosion on carbon steel pipes in heat exchanger of ethylene plant. Mater Corros [13] Chen FJ. Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant. Part I orrosion and wear. Eng Fail Anal 2014: 37: 29-41 [14 Chen F], Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant. Part ll [15] GB 9948-2006 Standards specification for seamless steel tubes for petroleum cracking(in Chinese). [18] Nasirpouri F, Mostafaei A, Fathyunes L Jafari R. Assessment of localized corrosion in carbon steel tube-grade AlSI 1045 used in output oil-gas essel of desalination unit in oil refinery industry Eng Fail Anal 2014: 40: 75-88.4. Conclusions 1. The material of heat exchange tubes in ammonia evaporators is confirmed to be 10 carbon steel and all testified to be qualified to requirements. 2. The connection between tubes and tubesheetis seal welding but without physical expansion. As a result, the welded joints are prone to cracking when subject to fluctuation of operating conditions. 3. Heat-exchange tubes in ammonia evaporators exhibit serious corroded defects and localized tube wall has thinned badly. The failure concretely happened as following steps: Firstly, the heat-exchange tubes suffered uniform corrosion and pitting in humid environment with presence of Cl, S and CO2. Besides, the interaction behavior of them accelerated material degradation process in weak sites, bringing about serious localized wall thinning of tubes. Then affected by temperature fluctuation and slight media erosion, corrosion layers gradually got cracking and some micro cracking initiated right from the pits. With its propagation, corrosion layer subsequently split into small pieces and scaled off the surface. As a result, the tube wall constantly thinned, leading to premature failure of ammonia evaporators in the end. 5. Prevention measures 1. The tube ends should be seal welding to tubesheet with physical expansion so as to increase their reliabilities. 2. Strictly control the contents of chloride ions and water vapor in ammonia evaporators introduced by equipment in upstream to avoid pitting on the heat exchange tubes caused by chloride ions. 3. Clean up the corrosion products on the tubes during shutdown maintenance of evaporators in case of under-deposit corrosion. References [1] Jahromi SAJ, AliPour MM, Beirami A. Failure analysis of 101-C ammonia plant heat exchange. Eng Fail Anal 2003;10(4):405–21. [2] Abbasfard H, Ghanbari M, Ghasemi A, Ghader S, Rafsajani HH, Ali Moradi A. Failure analysis and modeling of super heater tubes of a waste heat boiler thermally coupled in ammonia oxidation reactor. Eng Fail Anal 2012;26:285–92. [3] Bhaumik SK, Ramgaraju R, Parameswara MA, Bhaskaran TA, Venkataswamy A, Raghuram AC, et al. Failure of reformer tube of an ammonia plant. Eng Fail Anal 2002;9(5):553–61. [4] Arevalo A, Esparza P, Gomis Bas C, Morales J, Gonzalez S, de Sanchez SR. Corrosion on steam-side heat exchange tubes. Mater Perform 1996;35(1):67–8. [5] Ueda S, Onishi H, Okubo M, Takegawa T. Corrosion of ammonia plant heat exchanger. Ammonia Plant Saf Relat Facil 1978;20:98–102. [6] Sivaprasad S, Narang SK, Singh R. Failure of high pressure ammonia line in a fertilizer plant—a case study. Eng Fail Anal 2006;13(6):867–75. [7] Cui HX, Wang WQ, Li AJ, Li ML, Xu SG. Failure analysis of the brittle fracture of a thick-walled 20 steel pipe in an ammonia synthesis unit. Eng Fail Anal 2010;17:1359–76. [8] Li AJ, Wang WQ, Wang XM, Zhao D. Fatigue and brittle fracture of carbon steel process pipeline. Eng Fail Anal 2005;12:527–36. [9] Yang ZG, Gong Y, Yuan JZ. Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part I: Electrochemical corrosion. Mater Corros 2012;63(1):7–17. [10] Gong Y, Yang ZG, Yuan JZ. Failure analysis of leakage on titanium tubes within heat exchangers in a nuclear power plant. Part II: Mechanical degradation. Mater Corros 2012;63(1):18–28. [11] Gong Y, Yang ZG. Failure analysis of one peculiar ‘Yin-Yang’ corrosion morphology on heat exchanger tubes in purified terephthalic acid (PTA) dryer. Eng Fail Anal 2013;31:203–10. [12] Gong Y, Yang C, Yao C, Yang ZG. Acidic/caustic alternating corrosion on carbon steel pipes in heat exchanger of ethylene plant. Mater Corros 2011;62(10):967–78. [13] Chen FJ, Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant. Part I: Corrosion and wear. Eng Fail Anal 2014;37:29–41. [14] Chen FJ, Yao C, Yang ZG. Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant. Part II: Erosion and cavitation corrosion. Eng Fail Anal 2014;37:42–52. [15] GB 9948-2006 Standards specification for seamless steel tubes for petroleum cracking (in Chinese). [16] LaQue FL. Marine corrosion, causes and prevention. Hoboken, NJ, USA: John Wiley & Sons Inc.; 1975. 179. [17] Schutze M, Isecke B, Bender R. Corrosion protection against carbon dioxide. Frankfurt: Wiley-VCH; 2011. p. 63–92. [18] Nasirpouri F, Mostafaei A, Fathyunes L, Jafari R. Assessment of localized corrosion in carbon steel tube-grade AISI 1045 used in output oil-gas separator vessel of desalination unit in oil refinery industry. Eng Fail Anal 2014;40:75–88. S.-M. 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