Research On Migration Mechanism Of Corrosion In Water-Steam System In Power Plants

Improving the economic efficiency of coal-fired generating units and reducing pollutant emissions of coal-fired units is a becoming more and more important. Recently, units with high parameter and high capacity cause a lot of attention. However, the increasing parameter of steam gives new challenge to the safety management of heat pipe heating surface, steam-water corrosion risk becoming larger.This paper mainly focuses on the migration issues of corrosion product. Through theoretical analysis and calculation, we analyze the factors influencing the corrosion and corrosion product migration. The actual migration process of corrosion products in power plant is investigated by analyzing the operating data of units.The corrosion in the power plants is composed by flow accelerated corrosion (FAC) in the low-temperature portion and the high-temperature corrosion of the metal. FAC is the process of protective layer of magnetite dissolved in flowing water (single-phase) or wet steam (two-phase). High temperature corrosion of metal is the oxidation between metal and supercritical water or high temperature steam.Corrosion products including: Fe3O4、Fe(OH)2、α-Fe2O3、Fe2+、γ-Fe2O3、Fe(OH)2、Fe(OH)4-、Fe3+、Fe(OH)3. According to E-pH diagram, Fe2+can be judged as the most important corrosion product in the water system. Power plants should focus on monitoring Fe2+and its water-soluble derivative Fe(OH)+.For reducing corrosion in supercritical units, there may be a optimal oxygen content. The presence of oxygen promotes the formation of a protective oxide film, but long-term presence of excess oxygen will accelerate the formation and development of holes in the oxide layer.