T型三通管道冷热流体混合作用下循环热疲劳评估方法

An assessment method of thermal cycling induced fatigue of T-shaped junctions under combined action of hot and cold fluid

针对核电站中常见的用于冷热流体混合的T型三通管道,以往的研究多侧重混合流体的特性和温度分布预测,提出简化的热疲劳评估方法,分析了JSME导则的热疲劳评估方法的优缺点,并通过试验研究归纳流体混合特性。试验表明,随着动量比的增加,混合流体的温度波动强度同步增大,最大的无量纲方根温差为0.26;混合流体的温差大小对于温度波动强度的影响十分有限,仅为5%。试验同时表明,混合流体在0.05~2 Hz区间并没有典型的主导频率。基于以上结果,得到并提出了一种评估方法,将T型管道简化为轴对称管道模型,并将载荷简化为一系列正弦温度波动载荷,波动温差为名义温差的75%。经过对某核电站RHR系统检测中出现裂纹的T型管道开展分析,该部件在温差大于150℃冷热流体混合作用下的累计运行时间约为726 h,常见的压水堆核电站RHR系统运行规程规定的有效运行时间为450 h,其可以较好地管控疲劳风险;JSME方法分析预估疲劳寿命为1190 h,对本案例不是足够保守;使用本分析方法预估的疲劳寿命为587 h,可以更好地预测本案例的疲劳寿命,进而有效识别热疲劳风险和指导运行和维修。

With regards to T-shaped junctions commonly used for mixing hot and cold fluid in nuclear power stations,the previous studies mostly focused on the flow characteristics and temperature distribution of fluid mixture.A simplified assessment method for thermal fatigue was raised herein.The advantages and disadvantages of the JSME guideline for thermal fatigue assessment were analyzed.Furthermore,the mixing characteristics of the fluid were summarized through the laboratory tests.The tests show that temperature fluctuation strength increases with the increase of momentum ratio,the maximum normalized RMS temperature difference is 0.26;The temperature difference between hold and cold fluid has limited influence on temperature fluctuation strength,which is only 5%.Meanwhile,the tests show that there is no typical dominant frequency for the mixed fluid in the range of 0.05~2 Hz.Based on the above results,a simplified assessment method was obtained and proposed to simplify T-shaped junction as the axial symmetric pipe model,and simplify a series of sinusoidal thermal loads,the fluctuating temperature difference was defined as 75%of the nominal temperature difference.The tee junction with cracks found in the inspection of RHR system of a PWR nuclear station was analyzed.The accumulative running time of this component was evaluated to be about 726 h under the combined action of the hot and cold fluid with the temperature difference of more than 150℃,whereas the corresponding effective operation time is 450 h stipulated in the common RHR system operation guideline,so its fatigue risk can be well controlled;The fatigue life according to JSME guideline was 1190 h,which is not conservative enough for this case;The fatigue life estimated by the method of this study was 587 h,which can better predict the fatigue life in this case,and further effectively identify thermal fatigue risk and guide operation and overhaul.