Failure Analysis And Protective Measures Of Water Wall Cracking At Bottom Of Furnace

Thermal power generation,which accounts for 70% of the total power supply system in China,is the most important power generation mode.The work form of power station boiler is complex and poor working conditions,once the high temperature and high pressure steam pipeline cracking furnace tube leakage,will not only poses a great threat to the personal safety,and affect the overall safety running of the power plant boiler and the stability of regional power grid,so the boiler water fireplace tube leakage problem become the long-term impact of blasting safety in production important hidden danger.In this paper,the failure analysis of water-cooled fireplace tubes in the middle and bottom of furnace in two different power plants was carried out.The methods of macroscopic inspection,hardness test,ultrasonic thickness measurement,chemical composition analysis,mechanical properties test,metallography observation,scanning electron microscopy and other analysis methods were adopted.The failure mechanism of the microstructure,material composition and mechanical properties of the water-cooled fireplace pipe are analyzed and protective measures are put forward.The experimental results show that the damage mechanism of furnace tube is obviously different under different working temperature and pressure in the middle and bottom of furnace.Failure is due to the central chamber of a stove or furnace water wall furnace tube in the process of serving,inside the water reaches a certain concentration of hydrogen atom diffusion into the wall materials,hydrogen atoms react with carbon atoms in the substrate to generate methane,the methane accumulation in grain boundaries and phase boundaries and forming micro cracks,micro cracks with the increasing of methane gradually form macroscopic crack growth,finally cause the brittle fracture of the furnace tube;At the bottom of the furnace water wall tube failure is due to not standard in the process of repair welding operation at the end of the furnace tube fins produced two point welding arc pit,thus formed the crack source point,and heap welding seam welding temperature of the heating furnace tube surface and fast cooling,reformed the organization of furnace tube formed westergren body,lower the furnace tube of plasticity and toughness,deformation ability,then As a result,it is easier to crack under the action of additional stress.In addition,in view of the failure causes of the two accidents,the corresponding protection and measures are given from the two aspects of the material deterioration of the furnace tube of the power plant and the welding process of maintenance,in order to effectively prevent and reduce the cracking and failure of the water wall.