某电站高调门阀后热电偶套管在正常运行中多次发生断裂，使用最短的只有3个月。对断裂套管进行了断口宏、微观分析，并对失效套管固有频率进行了分析计算。结果表明，套管断裂是微动疲劳和整体疲劳相互作用的结果，过热蒸汽在套管背面流动变化引发的周期性压力波动是产生微动疲劳和整体疲劳的主要因素，套管固有频率处于蒸汽作用在套管上压力谱的频率范围内，加剧了热电偶套管的微动疲劳和整体疲劳。

The thermal coupling casing behind high-pressure adjusting steam stigma valve was broken during operation. One casing which has shortest life had worked only three monthes. In this paper, some analysis and calculation had been done. The results showed that there are some reasons which caused the fracture as follows: the interactive effect of integrated fatigue and fretting fatigue led to the failure, periodically pressure fluctuate in pipe behind the casing was the main reason which caused integrated fatigue and fretting fatigue, and the fatigue was accelerated because the nature frequency of this thermal coupling casing was within range of the pressure fluctuate which loaded in this casing.