Failure Analysis And Improvement Measures Of Boiler Pipes In Power Plants

Boiler pipe material failure has become an important factor affecting the safe and economic operation of power plants.Based on the analysis of various failure phenomena and failure causes of boiler pipes at home and abroad,this article uses macro analysis,chemical composition analysis,metallographic analysis,scanning electron microscope analysis,energy spectrum test and other methods to analyze the smoke at the tail of the low temperature reheater.Typical failure accidents such as cracking of tunnel,leakage of heating surface of boiler,tube burst of high temperature superheater were analyzed and studied.On this basis,measures to prevent boiler tube failure in power plants are summarized.(1)Through macro analysis,chemical composition inspection,non-metallic inclusions and metallographic analysis of the tail flue of the low-temperature reheater,it was found that the pipe thickness of the tail flue was uneven during the bending process,and the substrate had obvious bands.The microstructure causes uneven structure and reduces the plasticity and toughness of the steel.The presence of a decarburized layer of about 80-100 ?m on the outside of the pipe causes the surface hardness,tensile strength,and fatigue strength of the 20 G pipe to decrease.These factors lead to tube bursts.(2)Macro analysis,metallographic analysis,scanning electron microscopy,and energy spectrum testing of the root of the water-cooled wall weld found that there were large-sized unfused welding defects at the root of the water-cooled wall weld,which penetrated about 6 mm across the entire pipe wall,causing its leakage.;Pitting corrosion appeared on the inner surface of the fire side,uneven distribution of corrosion pits,some of them have been connected into a sheet to form larger pits,and penetration occurred at the leakage point;EDS spectrum shows the presence of phosphorus and chlorine in the corrosion products.The main cause of pitting corrosion is also the root cause of tube failure on the heating surface of the boiler.(3)Through the chemical composition,mechanical properties,hardness test,non-metallic inclusion detection,metallographic structure and grain size test of the high temperature superheater,it was found that the crack in the butt joint of the tube screen in the furnace originated from the weld between the steel pipe and the flat steel.At the weld toe,it extends longitudinally along the weld toe and expands towards the inner wall of the pipe,next to the butt weld at the site.When the screen is assembled,a certain length of mechanically welded flat steel near the on-site butt weld is torn apart from the middle to increase the degree of freedom of the steel pipe and facilitate docking.After the screen is joined,the torn flat steel is backfilled by manual welding.Welding causes secondary thermal effects on adjacent pipes,exacerbates the chrome-depletion phenomenon at grain boundaries,reduces the oxidation corrosion resistance of grain boundaries at this location in high-temperature operating environments,increases welding stress and structural stress,and causes cracking.The paper has 31 pictures,10 tables,and 62 references.