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ENVIRONMENTAL FATIGUE TESTING OF TYPE 304L STAINLESS STEEL U-BENDS IN SIMULATED PWR PRIMARY WATER

机译:模拟PWR初级水中304L不锈钢U形弯管的环境疲劳试验

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Environmental fatigue testing of small-scale austenitic stainless steel components under simulated pressurized water reactor (PWR) operating conditions was sponsored by the EPRI Materials Reliability Program (MRP) Fatigue Issue Task Group and the U.S. Department of Energy to fill in some important gaps in the knowledge base. An analysis and assessment of existing fatigue data for stainless steel exposed to the PWR primary environment identified a lack of data with respect to flow rate effects. The majority of existing data has been gained under static or quasi-static flow conditions, where the tendency to environmental enhancement of cyclic crack growth is generally expected to increase. However plant experience - where high-flow conditions prevail - shows significantly lower susceptibility to corrosion fatigue cracking.The main objective of the present test program was the identification of flow-rate effects on the initiation and growth of low-cycle corrosion fatigue (LCF) cracks in cold-drawn, 304L stainless steel tube U-bend specimens undergoing cyclic loading and simultaneous exposure to simulated PWR primary water on the inside of the tube. Use was made of a pre-existing facility at F-ANP in Germany where the experimental concept had been previously tested on carbon-steel U-bends. The test equipment was set up so as to allow direct comparison of results obtained under quasi-stagnant conditions (~0.005 m/s flow rate at the internal surface) with relatively high-flow conditions (~2.2 m/s flow rate).In accordance with literature data, PWR primary water was shown to have a significant effect on the high-temperature fatigue behavior of the bends, as demonstrated by the observed change in failure mode and location of cracking between baseline specimens (tested in nitrogen) and those bends exposed to simulated reactor coolant. Metallography and fractography suggest that the environment is acting by affecting both crack initiation and crack growth. In contrast to the situation for carbon steel, no beneficial effect of higher flow rate on the number of cycles to failure (leakage) was observed. The paper discusses further details of the environmental fatigue data obtained, including the effects of strain amplitude, strain rate and surface condition. It also provides a comparison of test results with the current ASME Section Ⅲ fatigue curves.
机译:在模拟加压水反应器(PWR)下的小型奥氏体不锈钢组分的环境疲劳试验由EPRI材料可靠性计划(MRP)疲劳问题任务组和美国能源部填补了一些重要差距知识库。暴露于PWR主要环境暴露于PWR初级环境的现有疲劳数据的分析和评估确定了关于流量效应的数据。大多数现有数据已经​​在静态或准静态流动条件下获得,其中循环裂纹增长的环境提高趋势通常会增加。然而,植物体验 - 在腐蚀疲劳裂解的高流量条件普遍稳定下显着降低了对腐蚀疲劳裂缝的敏感性。本试验计划的主要目的是鉴定对低循环腐蚀疲劳(LCF)的开始和生长的流量影响冷绘制的304L不锈钢管U形弯曲标本的裂缝遭受循环载荷和同时暴露于管内部模拟的PWR初级水。使用在德国F-ANP的预先存在的设施由实验概念以前在碳钢U形弯上进行了实验概念。建立了测试设备,以便直接比较在准停滞条件下获得的结果(内表面〜0.005米/升流速),具有相对高流量的条件(〜2.2米/秒)。根据文献数据,显示PWR初级水对弯曲的高温疲劳行为具有显着影响,如观察到的故障模式的变化和基线样本(在氮气中测试)和那些弯曲的裂缝的位置暴露于模拟反应器冷却剂。金相和断裂表明环境是通过影响裂纹启动和裂纹增长来作用。与碳钢的情况相比,观察到失效(泄漏)循环次数的更高流速的有益效果。本文讨论了所获得的环境疲劳数据的进一步细节,包括应变幅度,应变率和表面状况的影响。它还提供了测试结果与当前ASMEⅢ部分曲曲线的比较。

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