磨损对蒸汽发生器690合金传热管应力腐蚀裂纹萌生行为的影响

Effects of Wear on Stress Corrosion Cracking Initiation Behavior of Alloy 690 Steam Generator Tubes

摘要:

传热管是蒸汽发生器（SG）最关键的部件，起到一、二回路换热的作用，是防止放射性泄漏的重要安全屏障。在高温碱性溶液中进行了磨损690合金传热管的慢应变速率拉伸试验（SSRT）。采用扫描电子显微镜、电子背散射衍射和透射电子显微镜分析了690合金传热管的微动磨损和应力腐蚀裂纹（SCC）萌生行为。结果表明，SSRT试样呈现出典型的穿晶SCC特征，且随磨损深度增加，裂纹萌生数量和平均深度均增加，这可能与磨损表面留下的犁沟、剥层、微裂纹以及数十微米厚的残余应变层有关。基于SCC的滑移溶解/氧化机制，对磨损促进SCC裂纹萌生的过程进行了分析。

Abstract:

Tube bundles are the most critical components of steam generators in pressurized water plants. They are the heat exchange interface between primary and secondary circuits, acting as an important safety barrier to prevent the radioactive leakage. Stress corrosion cracking (SCC) initiation behavior of the worn alloy 690 tubes was investigated by slow strain rate tests (SSRT) in the high-temperature alkaline solution. The scanning electron microscope, electron backscatter diffraction and transmission electron microscope were used to analyze the fretting wear and SCC initiation behavior of alloy 690 tubes. Results show that SSRT specimens show typical transgranular SCC characteristics. The number of initiated cracks and their average depth are increased with increase in the wear degree, suggesting a wear-induced SCC initiation. This may have a relationship with the grooves, delamination, micro-cracks and residual strain layer with tens of micrometers in thickness left on the worn surface. Furthermore, a preliminary analysis on the possible procedure of wear-induced SCC initiation and further propagation during SSRT tests was carried out based on slip-dissolution/oxidation mechanism.