异种金属焊接接头材料高温高压水应力腐蚀的原位研究

Dissimilar metal weld joint is a kind of weak components in pressure boundary of primary circuit in PWR nuclear power plants (NPPs). Stress corrosion cracking (SCC) of the weld joint after long-term service in high temperature pressurized water is one of major failure modes for the key equipments serving in PWR primary circuit. The present project mainly investigates in-situ signals of electrochemical noise (EN) and acoustic emission (AE), mechanisms of EN and AE sources, and their correlation during SCC processes for the materials of nozzle safe end between reactor pressure vessel and main pipe in simulated PWR high temperature pressurized water, by using SCC tests, in-situ EN,AE and optical measurements, and thermodynamic analysis. The emphasis is laid on the relationship between crack initiation and propagation of SCC and typical EN and AE parameters. The effects of microstructure of the weld joint, temperature, applied potential and water chemistry on the above typical parameters will be inspected carefully. The aim is to clarify SCC failure mechanism for the dissimilar metal weld joint in high temperature pressurized water and to build up a SCC degradation criterion. The present work will pave both theoretical and technical ways for improving the on-line monitoring & inspecting capacity of corrosion degradation of key components in PWR NPPs, and also to ensure their safe service and to assess their service lives.

异种金属焊接接头是压水堆（PWR）核电站一回路压力边界的薄弱环节，其在高温高压水中长期服役时的应力腐蚀开裂（SCC）是导致PWR一回路关键设备失效的主要原因之一。本项目以PWR核电站压力容器与主管道连接部位的异种金属焊接接头材料为研究对象，运用原位电化学噪音（EN）和声发射（AE）测量及光学观测技术，结合高温高压水腐蚀热力学分析，研究异种金属焊接接头在模拟PWR一回路高温高压水中SCC的EN和AE信号特征、源机制及其相关性，确定SCC裂纹萌生与扩展与EN和AE特征参数的对应关系，考察焊接接头组织结构、温度、外加电位、水化学等因素的影响规律，阐明高温高压水SCC失效机理，建立异种金属焊接接头高温高压水SCC的损伤判据，为提高PWR核电站关键设备服役薄弱环节的在线监检测能力、保障其运行安全、评价其服役寿命提供理论和技术基础。

异种金属焊接接头由于存在成分与组织梯度变化、机械性能变化和较大残余应变，是压水堆（PWR）核电站一回路压力边界的薄弱环节，其在高温高压水中长期服役时的腐蚀与应力腐蚀（SCC）损伤是导致PWR一回路关键设备失效的主要原因之一。本项目表征了PWR核电站压力容器与主管道连接部位的低合金钢/不锈钢异种金属焊接接头材料的成分、组织结构和残余应变特征；成功研发了模拟核电高温高压循环水环境中原位声发射（AE）和电化学噪声（EN）联合测试技术，包括电化学测量探头、密封系统、波导杆及信号解析等，已授权三项国家发明专利；获得了焊接接头材料高温高压水腐蚀热力学和动力学规律，包括：高温多元体系的电位-pH关系、高温水腐蚀产物的溶解度与晶体结构特征、极化曲线、阻抗谱、EN特征等；结合恒载荷和慢拉伸SCC试验技术、原位AE和EN测量技术及表面和微观分析方法，获得了材料表面钝化膜破裂、亚稳点蚀形核、长大和再钝化过程的EN特征及水化学的影响规律；揭示了材料高温高压水SCC过程中的AE特征、区分了穿晶SCC和沿晶SCC的源机制，确定了SCC裂纹萌生与扩展与AE特征参数的对应关系；阐明了微观组织、温度、电位、PWR一回路注Zn水化学等因素对焊接接头材料腐蚀与开裂的影响规律及高温高压水SCC损伤机理，获得了SCC损伤的AE判据。研究结果为深入认识核电关键材料高温高压水腐蚀与SCC损伤过程和机理提供了直接的证据，从防止腐蚀损伤、抑制产物释放的角度建议了PWR核电站一回路水化学的优化控制方案，也为发展PWR核电站一回路压力边界设备材料服役过程中腐蚀损伤的在线监测技术及防护措施奠定了理论和技术基础。相关研究成果已应用于核电企业，并获中国核能行业协会科学技术发明奖一等奖及中国核工业集团公司科学技术奖三等奖。

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