核电主回路安全端金属焊接件结构特征与应力腐蚀行为研究
发布时间：2018-09-06 14:27
【摘要】：应力腐蚀开裂是压水堆核电站主回路安全端焊接接头的主要失效形式,威胁核电站的运行安全并造成巨大的经济损失。我国CPR1000压水堆核电站主管道采用SA508-309L/308L-316L安全端金属焊接件完成压力容器和主回路管道的连接。而目前国内尚未有该焊接件的应力腐蚀开裂行为研究。本论文分析了主回路安全端焊接件的结构特征,搭建了一套采用直流电位降技术的应力腐蚀开裂实验系统,并研究了焊接融合区域在高温高压水中的应力腐蚀裂纹扩展行为。采用改进的缝隙弯曲梁(CBB)实验研究了焊接熔合区的裂纹敏感性。搭建完成的DCPD系统能够准确测量高温高压水中裂纹的扩展长度,精度小于21μm。该系统同时具备溶解氧,温度,电导率等实验参数的监测功能。采用金相显微镜,扫描电子显微镜,能谱仪,维氏硬度计分析了核电主回路安全端金属焊接件的显微结构。实验结果表明,SA508低合金钢与309L/308L不锈钢异种焊接接头的低合金钢母材为贝氏体和铁素体结构,其低合金钢热影响区存在贫碳区,晶粒粗大区,细晶区等组织结构。焊材为奥氏体枝晶组织,δ铁素体分布在奥氏体晶粒间。低合金钢至焊材的焊接熔合区组织结构、硬度和化学成分变化显著。熔合线附近的焊材存在典型Type-Ⅰ、Type-Ⅱ晶界。316L不锈钢与308L不锈钢同种焊接接头的316L不锈钢母材为奥氏体组织,奥氏体晶界附近存在少量的6铁素体,热影响区存在MnS非金属夹杂物。熔合线两侧化学成分没有显著的变化,但硬度和铁素体含量发生了变化。研究了316L/308L同种焊接接头在除氧含硼锂高温高压水应力腐蚀开裂扩展行为。结果表明,采用最大应力强度因子为Kmax=25MPa·m1/2梯形波加载,裂纹扩展速率小于2×10-9mm/s。恒应力强度因子条件下,估算的裂纹扩展速率小于9×10-10mm/s。研究结果表明316L/308L同种焊接接头316L不锈钢热影响区在除氧的含硼锂高温高压水中应力腐蚀敏感性较低。改进的缝隙弯曲梁实验研究结果表明SA508-309L/308L异种焊接接头及堆焊层在除氧的高温高压水中也具有较低应力腐蚀敏感性。
[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，
本文编号：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，
本文编号：2226634
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