Analysis And Repair Research On Super Long Defects Of Drum In 660MW Power Plant Boiler

The boiler drum is one of the important equipment in the power plant boiler.It works in high temperature and high pressure environment.The boiler drum material must have the characteristics of high temperature toughness and its wall thickness is generally more than 100 mm.It is impossible to replace it if there is an excess defect of boiler drum,and the only way is to repair it at the site.It will cause serious defects by the additional stress of steam drum's own weight and connected with various functions cannot be eliminated.Therefore,how to repair the defects of the boiler drum has always been one of the world's problems in the power station boiler technology.Based on the above,the process of repairing the super-long defect of the boiler drum in a 660 MW power station imported from a domestic power plant was selected as the research content by this article.The analysis correctly the property and the cause of superlong defect of boiler drum was the based of making a reasonable repair method and repair.First,a method for the analysis of the physics and chemistry test of the super-long defect was developed in this article to analysis correctly the property and the cause of super-long defect tthrough the chemical analysis,hardness testing,metallographic analysis and scanning electron microscopy.Then,it has been analyzed that the deformation of the boiler drum during the repair process in combining with the operating characteristics of the steam drum.It has developed the repair methods that included the requirements for control of deformation during welding,heat treatment,etc.The pre-repair simulation repair test was conducted in order to verify the feasibility of the proposed repair method.Through the formulation of above methods and experimental verification,the super-long defect repair was completed at one time.The complete "physical examination" that include overall nondestructive testing,hydrostatic testing,and acoustic emission testing was performed in order to verify the quality of restoration.It was proved that the repair site meets the relevant requirements by the test results.The power station boiler has been safely and stably in commercial operation now.Therefore,it could be confirmed that the sampling physics and chemistry test methods and defect repair methods developed this article was feasible and effective.Through the study,the main conclusions of this article are as follows:1)The super-long defects are buried defects and have not been extended to the surface of the drum.2)The physicochemical test and analysis show that the residual welding slag in the matrix and the defects such as non fusion and gas blowholes has destroied the continuity of the matrix.Under the action of alternating load,the crack expands in the fatigue way.3)The pre-heating,half pass technology,pulse welding and partial heat treatment are all good procedures to reduce additional stress.Through the analysis and repair of seuper-long defects in the boiler drum of 660 MW power station,the useful experience for the repair of domestic large boiler boiler steam drums was provided.It also lays the foundation for the manufacture and repair of boiler drums for similar power plants.At the same time,it also fills the blank of similar defects repair in domestic highpower boiler boiler steam.