Investigation of Thermal Embrittlement of 17-4PH Stainless Steel Main Steam Isolation Valves
Investigation of Thermal Embrittlement of 17-4PH Stainless Steel Main Steam Isolation Valves
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DOI：
10.1007/s11668-021-01199-3
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发表时间：
2021-07-15
影响因子：
1.2
通讯作者：
Holden, Benjamin B.
中科院分区：
文献类型：
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作者：
Macha, John H.;Kirby, Matthew L.;Holden, Benjamin B.
核电站主蒸汽隔离阀（MSIV）阀杆组件多次发生故障。阀杆通常由H1100条件下的ASM SA 564 630级沉淀硬化钢（通常称为17-4 PH钢）组成。过去的几次阀杆故障都是由于热脆化造成的，在这种情况下，由于长期暴露在大约260-316摄氏度（500-600华氏度）的温度范围内引起的微观结构变化，阀杆基体材料表现出机械性能下降。脆化MSIV阀杆的失效机制包括在电厂停堆期间因测试驱动产生的载荷而突然断裂，以及蒸汽流振动导致的运行中疲劳裂纹扩展（FCG）。三个MSIV阀杆在压水反应堆（PWR）中运行九年后被拆除，并进行了力学和机械评价，以确定热脆化的严重程度和程度。这些评价的结果用于开发基于条件的股骨柄脆化诱导失效随时间推移的风险预测。结果发现，从使用中取出的股骨柄材料没有表现出明显的冶金或机械脆化迹象，并且材料在当前老化条件下失效的可能性很小。
Multiple failures of main steam isolation valve (MSIV) stem components have occurred at nuclear power plants. Stems are typically composed of ASM SA564 Grade 630 precipitation hardened steel, commonly known as 17-4 PH steel, in the H1100 condition. Several past valve stem failures have been attributed to thermal embrittlement, a condition under which the stem base material exhibits degraded mechanical properties due to microstructural changes induced by long-term exposure to a temperature range of approximately 260-316 degrees C (500-600 degrees F). Failure mechanisms of embrittled MSIV stems include sudden fracture due to loads from test actuations during plant outages as well as in-service fatigue crack growth (FCG) caused by vibrations from the steam flow. Three MSIV stems were removed from service after nine years in a pressurized water reactor (PWR) and were metallurgically and mechanically evaluated to determine the severity and extent of thermal embrittlement present. Findings from these evaluations were used to develop a condition-based projection of risk over time of the embrittlement-induced failure of the stems. It was found that the stem material removed from service did not exhibit significant metallurgical or mechanical evidence of embrittlement and that the probability of failure of the material in its current aged condition was small.