循环流化床锅炉快速磨损失效机理

Mechanism of rapid erosion failure in CFB boilers

用扫描电子显微镜(SEM)对实际运行后的循环流化床(CFB)锅炉水冷壁管局部磨损区域的微观形貌进行观察和分析,研究了局部磨蚀坑的形成过程,提出了CFB锅炉水冷壁快速磨损失效的新机制和“微区凿削”磨损模型。结果表明:水冷壁失效主要是高攻击角颗粒撞击磨损与低攻击角颗粒冲刷磨损结合的局部快速冲蚀形成小而深的磨蚀坑,磨蚀坑下部台阶磨损失效的微观机制是撞击-疲劳-塑性变形-表面微裂纹-冲刷-脱落,磨损速率最快;底部磨损失效的微观机制为冲刷-切削-撞击-剥落,磨损速率较快;两侧面的失效机制为氧化膜破碎脱落,磨损速率最慢。3种磨损机制的综合作用使局部磨蚀坑迅速向深部发展,从而使水冷壁管快速减薄失强而引起爆管事故。

Based on the observation of micro-appearance of the local erosion with scan electrical microscope （SEM）, the rapid failure process of CFB boiler tubes was studied. A new kind of erosion mechanism and model named tiny zone chisel dig （TZCD） was proposed. The SEM results indicate that once the TZCD erosion began, it would be lasting and a tiny deep hole formed during a short of time. It is the local TZCD erosion which caused the rapid failure of robes. The combination of impact with steep impingement angles and scour wear with shallow angles by the particles composes the erosion mechanism. The process of the failure behavior of the deep area developed as follows： the elastic fatigue emerged firstly under the particle impact, then ductility deformations produced, and then surface micro-cracks came into being, and the microchips flaked away at last. In this process, the erosion rate was very high. The failure process on the bottom of the erosion hole shows the relatively high wear rate characterized by more micro-scour together with little impact erosion. The erosion wastage of the oxides on the sh）pe of the both sides of the hole forms another failure, process with the lowest erosion rate. The small-area erosion develops rapidly in depth under the effect of three processes until the failure accident happens in a short time.