核電主回路安全端金屬焊接件結構特征與應力腐蝕行為研究
發(fā)布時間：2018-09-06 14:27
【摘要】：應力腐蝕開裂是壓水堆核電站主回路安全端焊接接頭的主要失效形式,威脅核電站的運行安全并造成巨大的經濟損失。我國CPR1000壓水堆核電站主管道采用SA508-309L/308L-316L安全端金屬焊接件完成壓力容器和主回路管道的連接。而目前國內尚未有該焊接件的應力腐蝕開裂行為研究。本論文分析了主回路安全端焊接件的結構特征,搭建了一套采用直流電位降技術的應力腐蝕開裂實驗系統(tǒng),并研究了焊接融合區(qū)域在高溫高壓水中的應力腐蝕裂紋擴展行為。采用改進的縫隙彎曲梁(CBB)實驗研究了焊接熔合區(qū)的裂紋敏感性。搭建完成的DCPD系統(tǒng)能夠準確測量高溫高壓水中裂紋的擴展長度,精度小于21μm。該系統(tǒng)同時具備溶解氧,溫度,電導率等實驗參數(shù)的監(jiān)測功能。采用金相顯微鏡,掃描電子顯微鏡,能譜儀,維氏硬度計分析了核電主回路安全端金屬焊接件的顯微結構。實驗結果表明,SA508低合金鋼與309L/308L不銹鋼異種焊接接頭的低合金鋼母材為貝氏體和鐵素體結構,其低合金鋼熱影響區(qū)存在貧碳區(qū),晶粒粗大區(qū),細晶區(qū)等組織結構。焊材為奧氏體枝晶組織,δ鐵素體分布在奧氏體晶粒間。低合金鋼至焊材的焊接熔合區(qū)組織結構、硬度和化學成分變化顯著。熔合線附近的焊材存在典型Type-Ⅰ、Type-Ⅱ晶界。316L不銹鋼與308L不銹鋼同種焊接接頭的316L不銹鋼母材為奧氏體組織,奧氏體晶界附近存在少量的6鐵素體,熱影響區(qū)存在MnS非金屬夾雜物。熔合線兩側化學成分沒有顯著的變化,但硬度和鐵素體含量發(fā)生了變化。研究了316L/308L同種焊接接頭在除氧含硼鋰高溫高壓水應力腐蝕開裂擴展行為。結果表明,采用最大應力強度因子為Kmax=25MPa·m1/2梯形波加載,裂紋擴展速率小于2×10-9mm/s。恒應力強度因子條件下,估算的裂紋擴展速率小于9×10-10mm/s。研究結果表明316L/308L同種焊接接頭316L不銹鋼熱影響區(qū)在除氧的含硼鋰高溫高壓水中應力腐蝕敏感性較低。改進的縫隙彎曲梁實驗研究結果表明SA508-309L/308L異種焊接接頭及堆焊層在除氧的高溫高壓水中也具有較低應力腐蝕敏感性。
[Abstract]:Stress corrosion cracking (SCC) is the main failure form of welded joints in the main loop of PWR nuclear power station, which threatens the operation safety of nuclear power station and causes huge economic losses. The main pipeline of CPR1000 PWR nuclear power station uses SA508-309L/308L-316L safety end metal welding to connect the pressure vessel and the main loop pipeline. At present, there is no research on the stress corrosion cracking behavior of the welding piece in China. In this paper, the structural characteristics of the main circuit safety end welds are analyzed, a set of stress corrosion cracking experimental system using DC potential drop technique is built, and the stress corrosion crack propagation behavior of welding fusion region in high temperature and high pressure water is studied. The crack sensitivity of welding fusion zone was studied by improved (CBB) experiment of slot bending beam. The DCPD system can accurately measure the length of crack propagation in high temperature and high pressure water, and the accuracy is less than 21 渭 m. The system also has the monitoring function of dissolved oxygen, temperature, conductivity and other experimental parameters. Metallographic microscope, scanning electron microscope, energy spectrometer and Vickers hardness meter were used to analyze the microstructure of the safety end metal welds of nuclear power main circuit. The experimental results show that the base metal of the dissimilar welded joint of SA508 low alloy steel and 309L/308L stainless steel is bainite and ferrite structure, and the low alloy steel's heat-affected zone has carbon poor zone, coarse grain area, fine grain area and so on. The welding material is austenitic dendritic structure and 未 ferrite is distributed among austenite grains. The microstructure, hardness and chemical composition of the welding fusion zone from low alloy steel to welding material changed significantly. In the welding material near the fusion line, there is austenitic structure in the 316L stainless steel base metal of typical Type- 鈪，
本文編號：2226634
[Abstract]:Stress corrosion cracking (SCC) is the main failure form of welded joints in the main loop of PWR nuclear power station, which threatens the operation safety of nuclear power station and causes huge economic losses. The main pipeline of CPR1000 PWR nuclear power station uses SA508-309L/308L-316L safety end metal welding to connect the pressure vessel and the main loop pipeline. At present, there is no research on the stress corrosion cracking behavior of the welding piece in China. In this paper, the structural characteristics of the main circuit safety end welds are analyzed, a set of stress corrosion cracking experimental system using DC potential drop technique is built, and the stress corrosion crack propagation behavior of welding fusion region in high temperature and high pressure water is studied. The crack sensitivity of welding fusion zone was studied by improved (CBB) experiment of slot bending beam. The DCPD system can accurately measure the length of crack propagation in high temperature and high pressure water, and the accuracy is less than 21 渭 m. The system also has the monitoring function of dissolved oxygen, temperature, conductivity and other experimental parameters. Metallographic microscope, scanning electron microscope, energy spectrometer and Vickers hardness meter were used to analyze the microstructure of the safety end metal welds of nuclear power main circuit. The experimental results show that the base metal of the dissimilar welded joint of SA508 low alloy steel and 309L/308L stainless steel is bainite and ferrite structure, and the low alloy steel's heat-affected zone has carbon poor zone, coarse grain area, fine grain area and so on. The welding material is austenitic dendritic structure and 未 ferrite is distributed among austenite grains. The microstructure, hardness and chemical composition of the welding fusion zone from low alloy steel to welding material changed significantly. In the welding material near the fusion line, there is austenitic structure in the 316L stainless steel base metal of typical Type- 鈪，
本文編號：2226634
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