汽轮机低压调节级动叶片水蚀分析

Analysis on Water-Erosion of Moving Blade in Low-pressure Control Stage of a Steam Turbine

烯烃装置裂解气压缩机组大检修期间发现汽轮机低压调节级动叶片"蜂窝状点蚀"现象比较严重,对应的静叶片及后2级静叶片也有点蚀现象。分析发现利用湿蒸汽对汽轮机吹扫的方法存在缺陷,在主蒸汽降温的过程中只考虑了高压缸防水蚀的影响,忽略了抽汽背压不可控,导致低压缸进汽压力相对该处的进汽温度过高,部分蒸汽产生冷凝液,蒸汽中夹带的水滴撞击在动叶片出汽边背弧上,致使材料疲劳破坏形成水蚀。根据操作经验和理论分析确定:吹扫工况时,低压调节级的进汽压力应低于170℃时的蒸汽饱和压力,抽汽压力应低于0.8 MPa,并利用蒸汽管网改造,控制抽汽压力在0.4～1.6 MPa。通过优化操作参数完全可以避免低压调节级动叶片水蚀。

Serious ＂honeycomb pitting corrosions＂ were found in the moving blades of the steam turbine＇s low -pressure control stage in the overhaul of the cracked gas compressor train, corresponding stationary blades and after the two - stage stationary blades also had ＂pitting corrosion＂. The analysis concluded that there was negligence in the flushing of steam turbine with wet steam. In the process of lowering the steam temperature, only the impact of water erosion of HP cylinder was considered and uncontrollable extracted steam pressure was ignored. These led to excessive higher temperature of inlet steam as compared with the pressure. Condensate was formed from some steam, water droplets entrained in the steam impinged on the back arc of the moving blades, the material was fatigued and water erosion was formed. Based upon the operating experience and theoretical analysis, in flushing operation, the pressure of inlet steam of LP control stage should be lower than steam saturation steam at 170℃, and the pressure of extracted steam should be lower than 0.8 MPa. The pressure of extracted steam was controlled within 0. 4 1.6 MPa by revamping of steam pipe network. In addition, the optimization of operating parameters can completely eliminate the water erosion of low - pressure control stage＇ s moving blade.