3-15. In-situ monitor technique for stress corrosion cracking initiation of multi-specimens in typical environment

Zhiming Zhang, Jianqiu Wang*, En-Hou Han, Wei Ke

Key Laboratory of Nuclear Materials and Safety Assessment, Chinese Academy of Sciences, Liaoning Key Laboratory for Safety and Assessment Technique of Nuclear Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Abstract: Stress corrosion cracking (SCC) has become one of the main failure causes for the key materials used in the nuclear power plants (NPPs), during the past decades. It has been found that the initiation time accounts for about 90% of the total time of structural failure due to SCC. Thereby, it is of great importance to obtain the effective crack initiation time and understand the cracking rules or mechanisms of nuclear key materials in the simulated serviced environments, for the evaluation of service safety, service life, and also the aging management of NPPs. The crack initiation of materials in simulated high temperate and high pressure water is not only very slow, but also affected by many factors, such as material microstructure, surface state and so on, therefor, the crack initiation is random in most cases. In general, one autoclave is equipped with one tensile rod and only one sample could be tested in a single experiment. The test effectiveness of this kind of test is too low to finish the crack initiation test of various nuclear materials in the complex serviced environments. In this case, a kind of test, during which many samples could be examined simultaneously is needed. Meanwhile, the in-situ monitoring of the crack initiation is also should be solved. A kind of in-situ monitor technique for SCC initiation of multi-specimens in typical environment is developed in our lab. The practical water chemistry of NPPs could be simulated and controlled well. Moreover, 18 samples could be tested at the same time with a specially designed tensile load system, of which there are three tensile rods and 6 samples are placed in one rod. The direct current potential drop and electrochemical noise techniques are employed to in-situ monitor the crack initiation.

Keywords: Multi-specimens, Stress corrosion cracking, Crack initiation, Monitor technique

 典型环境中多样品同时加载应力腐蚀裂纹萌生测试技术

张志明 王俭秋* 韩恩厚 柯 伟 

中国科学院金属研究所，中国科学院核用材料与安全评价重点实验室，辽宁省核电材料与安全评价技术重点实验室，辽宁沈阳，110016 

摘要:应力腐蚀是核电站关键材料环境失效的主要形式之一。应力腐蚀裂纹萌生寿命约占结构 因应力腐蚀失效断裂的总时间的 90%。因而获得核电关键材料在模拟核电环境的有效裂纹萌生 时间、掌握裂纹萌生规律，对于评估其服役安全、服役寿命以及开展核电站的老化管理至关重 要。材料在模拟核电高温高压水环境中不仅裂纹萌生速率极慢，而且受微观结构、表面状态等 多因素影响，裂纹萌生发生的随机性很大。在高温高压水中进行应力腐蚀测试，通常一台高压 釜仅有一个拉伸轴，每次实验时仅能完成一个样品的测试。这种效率非常低，根本无法完成核 电多种材料在多因素下的裂纹萌生测试以及相应萌生机制的研究。这就需要开展多样品、长时 间的裂纹萌生实验。针对核电的特殊服役环境，就需要在高温高压水环境中实现原位的多轴、 多样品同时拉伸加载，并获得小裂纹萌生的弱电位降信号和应变电极原位电化学噪声信号。目前，由于缺乏对应力腐蚀裂纹萌生规律的认识，无法对关键结构进行延寿和全寿命评估。因此 获得高温高压水中应力腐蚀裂纹萌生时间的直接有效数据，是目前核电建造、运营、老化管理 和高温高压水中材料的应力腐蚀控制机理亟待研究和解决的难点。

      针对这一测试难点，在实验室研制了一套模拟核电高温高压水中多样品应力腐蚀裂纹萌生 原位测试装置。该装置主要由核电高温水环境模拟系统、高温高压水三轴多样品加载系统、高 温高压水直流电位降系统和高温高压水电化学噪声测试系统四部分构成。装置的环境模拟系统 可以有效地模拟和控制核电关键设备材料服役的环境条件，包括水温度、压力和水化学(溶解 氢、溶解氧、pH 值、电导率)等。装置的高温高压水三平行轴多样品加载系统，可以实现一次 升温进行 18 个有效样品的同时测量(每个拉伸轴放置 6 个棒状样品)，节约时间，减少能耗。 装置的原位高温高压水直流电位降系统和高温高压水电化学噪声测试系统，利用高分辨率的纳 伏表和高输入阻抗的电化学工作站，能够原位实时监测样品在应力腐蚀裂纹萌生过程中的电位 变化和电化学信号。通过在同一高压釜内放置多参比试样，可以有效抵消由于水流、温度和压 力的波动等因素造成的信号干扰，确保采集到有效的信号。

       建成的测试装置以及测试技术，可以精确模拟核电站一、二回路高温高压水化学环境，实现材料在高温高压水环境中应力腐蚀裂纹萌生的原位监检测，研究微观结构、载荷水平、水化学条件、有害离子等对应力腐蚀裂纹萌生寿命的影响，为判断材料是否发生应力腐蚀开裂和评估核电关键材料的服役寿命提供关键基础数据。
关键词:多样品;应力腐蚀;裂纹萌生;测试技术