Engineering Failure Analysis 37(2014)42-52 Contents lists available at Science Direct VGINEFNING Engineering Failure Analysis ELSEVIER journalhomepagewww.elsevier.com/locate/engfailanal Failure analysis on abnormal wall thinning of heat-transfer CrossMark titanium tubes of condensers in nuclear power plant Part ll: erosion and cavitation corrosion Fei-Jun Chen, Cheng Yao, Zhen-Guo Yang epartment of Materials Science, Fudan University, Shanghai 200433, PR China ARTICLE INFO A BSTRACT In Part I of the failure analysis on abnormal wall thinning of heat-transfer titanium tubes eived 24 March 2013 sed in Accepted 19 Nover Available online 4 December 2013 abnormal thinning that commonly happened at the contact part between the tubes and the support plates. This kind of failure was the mainstream failure type in our case and ne main causes were found to be eccentric contact wear and three-body contact m tube Doted in processing defect of internal borings, corrosion products deposit and sagging, cles. however there still some individual failure tubes with different failure sites and modes and were located under the bypass pipes at the shoulder of the tube tower instead of in its lower part, obviously telling another failure story. In Part ll of the Cavitation corrosion failure analysis, material analysis, metallographic examination, mechanical performance tests, macro and microstructure analysis and composition analysis were conducted. The failure causes were found to be erosion and cavitation corrosion and the synergetic effect of them. Finally, corresponder ntermeasures uggested. e 2013 Elsevier Ltd. All rights reserved. 1 Introduction Since nuclear power was utilized, safety concerns have never stopped to bother us. from the disaster of Chernobyl in Russia decades ago, to the nuclear leak in Fukushima in the last two years, historical lessons written in blood have taught us that every detail in a nuclear power station is of critical importance and not a single tiniest potential peril can be ignored. The heat-transfer titanium tubes in condensers of the two 700 MW CANDU units in China- the first and only two pres- surized heavy water reactor(PHWR)units in the country-have encountered abnormal tube wall thinning with a design life of 40 years, the condensers were forced to temporarily stop operation after only 8 years in service because unexpected wall thinning problems were found on the heat-transfer titanium tubes, bringing about heavy economic loss and potential safety threat. Our team was asked to conduct failure analysis of the tubes. The tubes are made of industrial pure titanium in correspondence to Chinese brand TAl, with the length of 17370 mm, and specifications of 25. 4 mm x 0.5 mm(outside diameter x wall thickness). All these specifications have also been mentioned in Part I [ 1] of the failure analysis. Among the dozens of tube samples we got, most of them presented similar failure modes at similar positions. After detailed analysis by various techniques, we primarily ascribed most of the failure cases to eccentric contact wear al three-body contact wear rooted in processing defect of internal borings, corrosion products deposit and sagging, and foreig particles, discussed in Part I 1 of the failure analysis. However, we still found another kind of failure case with distinct appearance and failure positions. When we conducted inspection inside the condenser, we discovered the bypass pipes, onding author.Tel:+862165642523;fax:+862165103056 E-mailaddress:zgyang@fudan.edu.cn(Z-G.Yang). 1350-6307/S-see front 2013 Elsevier Ltd. All rights reserved.Failure analysis on abnormal wall thinning of heat-transfer titanium tubes of condensers in nuclear power plant Part II: Erosion and cavitation corrosion Fei-Jun Chen, Cheng Yao, Zhen-Guo Yang ⇑ Department of Materials Science, Fudan University, Shanghai 200433, PR China article info Article history: Received 24 March 2013 Accepted 19 November 2013 Available online 4 December 2013 Keywords: Titanium tube Wall thinning Failure analysis Erosion Cavitation corrosion abstract In Part I of the failure analysis on abnormal wall thinning of heat-transfer titanium tubes used in condensers in nuclear power plant, we analyzed the causes and mechanisms of abnormal thinning that commonly happened at the contact part between the tubes and the support plates. This kind of failure was the mainstream failure type in our case and the main causes were found to be eccentric contact wear and three-body contact wear rooted in processing defect of internal borings, corrosion products deposit and sagging, and foreign particles. However, there were still some individual failure tubes with different failure sites and modes and were located under the bypass pipes at the shoulder of the tube tower instead of in its lower part, obviously telling another failure story. In Part II of the failure analysis, material analysis, metallographic examination, mechanical performance tests, macro- and microstructure analysis and composition analysis were conducted. The failure causes were found to be erosion and cavitation corrosion and the synergetic effect of them. Finally, corresponding countermeasures were suggested. 2013 Elsevier Ltd. All rights reserved. 1. Introduction Since nuclear power was utilized, safety concerns have never stopped to bother us. From the disaster of Chernobyl in Russia decades ago, to the nuclear leak in Fukushima in the last two years, historical lessons written in blood have taught us that every detail in a nuclear power station is of critical importance and not a single tiniest potential peril can be ignored. The heat-transfer titanium tubes in condensers of the two 700 MW CANDU units in China – the first and only two pres￾surized heavy water reactor (PHWR) units in the country – have encountered abnormal tube wall thinning. With a design life of 40 years, the condensers were forced to temporarily stop operation after only 8 years in service because unexpected wall thinning problems were found on the heat-transfer titanium tubes, bringing about heavy economic loss and potential safety threat. Our team was asked to conduct failure analysis of the tubes. The tubes are made of industrial pure titanium in correspondence to Chinese brand TA1, with the length of 17370 mm, and specifications of 25.4 mm 0.5 mm (outside diameter wall thickness). All these specifications have also been mentioned in Part I [1] of the failure analysis. Among the dozens of tube samples we got, most of them presented similar failure modes at similar positions. After detailed analysis by various techniques, we primarily ascribed most of the failure cases to eccentric contact wear and three-body contact wear rooted in processing defect of internal borings, corrosion products deposit and sagging, and foreign particles, discussed in Part I [1] of the failure analysis. However, we still found another kind of failure case with distinct appearance and failure positions. When we conducted inspection inside the condenser, we discovered the bypass pipes, 1350-6307/$ - see front matter 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engfailanal.2013.11.002 ⇑ Corresponding author. Tel.: +86 21 65642523; fax: +86 21 65103056. E-mail address: zgyang@fudan.edu.cn (Z.-G. Yang). Engineering Failure Analysis 37 (2014) 42–52 Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal