超超临界锅炉过热器管超温蠕变应力松弛规律研究

超超临界锅炉高温过热器集箱出口区域的过热器管易处于超温运行的环境，产生蠕变应力松弛导致材料失效. 基于Norton蠕变模型，以烟气温度750℃、蒸汽温度600℃、蒸汽压力26 MPa的运行工况，模拟T91过热器管壁在长时间热诱导中产生的应力松弛行为及蠕变分布. 模拟结果显示，过热管应力松弛现象首先发生在管内壁面，随着时间累计沿着径向方向扩散；10000 h后内壁面出现应力松弛且松弛加速；同时管壁面在应力松弛的过程中发生高温蠕变行为，且蠕变行为首先出现在内壁面并沿着径向扩散，内壁面蠕变程度高于外壁面；10000 h后管壁面厚度开始减薄. 研究结果表明:超超临界锅炉过热器管超温运行10000 h是蠕变应力松弛到蠕变损伤的时间拐点.

Study on relaxation rule of over temperature creep stress in superheater tube of ultra-supercritical boiler

The superheater tube in the outlet area of the high-temperature superheater box of ultra-supercritical boiler is easy to be exposed to overtemperature environment, resulting in creep stress relaxation and material failure. Based on Norton creep model, the stress relaxation behavior and creep distribution of T91 superheater tube wall during long-term thermal induction were simulated under the operating conditions of flue gas temperature of 750℃, steam temperature of 600℃ and steam pressure of 26 MPa. The simulation results show that stress relaxation phenomenon of the heat pipe firstly occurs on the inner wall and spreads along the radial direction with time accumulation. After 10000 h, the inner wall surface appears stress relaxation and relaxation accelerates. At the same time, high temperature creep behavior also occurs on the tube wall during the stress relaxation process, and the creep behavior firstly appears on the inner wall and spreads along the radial direction, and the creep degree of the inner wall is higher than that of the outer wall. After 10000 h, the thickness of pipe wall begins to decrease. The results show that the overtemperature operation of superheater tube of ultra-supercritical boiler for 10000 h is the time point from creep stress relaxation to creep damage.