Case Studies in Engineering Failure Analysis 3(2015)52-61 Contents lists available at Science Direct Case Studies in Engineering Failure Analysis ELSEVIER journalhomepagewww.elsevier.com/locate/csefa Case study Failure analysis on unexpected wall thinning CrossMark of heat-exchange tubes in ammonia evaporators Shi-Meng Hu, Sheng-Hui Wang Zhen-Guo Yang Department of materials Science, Fudan University, Shanghai 200433, PR China Shanghai Institute of Special Equipment Inspection and Technical Research, Shanghai 200333, PR China ARTICLE INFO ABSTRACT Article h A failure incident of heat-exchange tubes in ammonia evaporators, which suffered from Received 7 october 2014 expected wall thinning after only one-year service with respect to their original design Accepted 13 January 2015 lifetime of fifteen years, was reported and carefully analyzed. After overall inspection, many Available online 28 January be walls in the evaporators were found to experience severe degradations at both sides with distinct corroded defects and general cracking of corrosion layers. Thus, ce nvestigations including external appearance, microscopic morphology and chemical omposition were carried out by using a series of characterization methods. The analysis results demonstrated that the unexpected wall thinning of tubes was primarily ascribed to Carbon steel ultiple corrosion factors including uniform corrosion, pitting and interaction behavior Failure analysis between them. Relative failure mechanisms were discussed in detail and prevention Corrosion neasures were also proposed for ammonia evaporators under similar operating condition. @2015 The Authors Published by Elsevier Ltd. This is an open access article under the cc By-nC-ndlicense(http://creativecommonsorg/licenses/by-nc-nd/4.0/). 1. Introduction Recently there occurred an unexpected failure incident of ammonia evaporators in a polyurethane plant, which is located at the coastal area of China and managed by a foreign company. These ammonia evaporators play critical roles for the whole system of circulating cooling process in core plant, mainly used to manufacture 2, 4-tolylene diisocyanate(tDi). Herein, the evaporators are employed to exchange heat between ammonia in shell side with phase change and evaporation, and o-dichlorobenzene(odB)in tube side, which has been utilized in upstream process to cool various products in advance. The accurate operation parameters of evaporators are listed in Table 1. Each evaporator is a type of tubular heat xchanger with 6850 heat-exchange tubes(10 carbon steel, 25 mm x 2 mm) arranged as a horizontal tube bundle in the shell. They are mounted by tubesheet(16Mnlll) welded to at both ends, as well as 8 perforated baffle plates(Q345R steel) sustained in the middle with interval distance of 800 mm evenly, shown in Fig. 1 The unit was put into service in April 2011 with design lifetime of about fifteen years. But within only one year, two evaporators encountered with unexpected failure to different extent in succession, namely sudden leakage and serious tube- wall thinning. Particularly, some tube-wall thickness has decreased up to 40% in localized defect area detected by X-ray on- site inspection. This premature failure affected whole circulating system gravely and enormous losses in finance and energy cannot be avoided In addition, it appeared to be more severe for the units given that they had operated for such a short time Corresponding author. Tel: +86 21 65642523: fax: +86 21 65103056 mail address: zoya 2213-2902/e2015TheAuthorsPublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCcBy-nC-ndlicense(http://creativecommons.orgCase study Failure analysis on unexpected wall thinning of heat-exchange tubes in ammonia evaporators Shi-Meng Hu a , Sheng-Hui Wang a,b , Zhen-Guo Yang a, * aDepartment of Materials Science, Fudan University, Shanghai 200433, PR China b Shanghai Institute of Special Equipment Inspection and Technical Research, Shanghai 200333, PR China 1. Introduction Recently there occurred an unexpected failure incident of ammonia evaporators in a polyurethane plant, which is located at the coastal area of China and managed by a foreign company. These ammonia evaporators play critical roles for the whole system of circulating cooling process in core plant, mainly used to manufacture 2,4-tolylene diisocyanate (TDI). Herein, the evaporators are employed to exchange heat between ammonia in shell side with phase change and evaporation, and o-dichlorobenzene (ODB) in tube side, which has been utilized in upstream process to cool various products in advance. The accurate operation parameters of evaporators are listed in Table 1. Each evaporator is a type of tubular heat exchanger with 6850 heat-exchange tubes (10 carbon steel, 25 mm 2 mm) arranged as a horizontal tube bundle in the shell. They are mounted by tubesheet (16MnIII) welded to at both ends, as well as 8 perforated baffle plates (Q345R steel) sustained in the middle with interval distance of 800 mm evenly, shown in Fig. 1. The unit was put into service in April 2011 with design lifetime of about fifteen years. But within only one year, two evaporators encountered with unexpected failure to different extent in succession, namely sudden leakage and serious tube￾wall thinning. Particularly, some tube-wall thickness has decreased up to 40% in localized defect area detected by X-ray on￾site inspection. This premature failure affected whole circulating system gravely and enormous losses in finance and energy cannot be avoided. In addition, it appeared to be more severe for the units given that they had operated for such a short time. Case Studies in Engineering Failure Analysis 3 (2015) 52–61 A R T I C L E I N F O Article history: Received 7 October 2014 Received in revised form 13 January 2015 Accepted 13 January 2015 Available online 28 January 2015 Keywords: Ammonia evaporator Wall thinning Carbon steel Failure analysis Corrosion A B S T R A C T A failure incident of heat-exchange tubes in ammonia evaporators, which suffered from unexpected wall thinning after only one-year service with respect to their original design lifetime of fifteen years, was reported and carefully analyzed. After overall inspection, many tube walls in the evaporators were found to experience severe degradations at both sides with distinct corroded defects and general cracking of corrosion layers. Thus, comprehensive investigations including external appearance, microscopic morphology and chemical composition were carried out by using a series of characterization methods. The analysis results demonstrated that the unexpected wall thinning of tubes was primarily ascribed to multiple corrosion factors including uniform corrosion, pitting and interaction behavior between them. Relative failure mechanisms were discussed in detail and prevention measures were also proposed for ammonia evaporators under similar operating condition. 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). * Corresponding author. Tel.: +86 21 65642523; fax: +86 21 65103056. E-mail address: zgyang@fudan.edu.cn (Z.-G. Yang). Contents lists available at ScienceDirect Case Studies in Engineering Failure Analysis journal homepage: www.elsevier.com/locate/c sefa http://dx.doi.org/10.1016/j.csefa.2015.01.002 2213-2902/ 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).