Fracture Mechanical Performance Analysis And Damage Mechanism Research Of HP40Nb Furnace Tube

In petrochemical enterprises,the hydrogen manufacturing converted furnace,which under the high temperature,high pressure and hydrogen environment,is the core device of hydrogen manufacturing unit,with its service conditions being very bad.Unfortunately,the high temperature furnace tube,a core part in hydrogen manufacturing converted furnace,often failed in service with its cracking,which not only brings huge economic losses to enterprises,but also causes serious safety accidents.Therefore,it is necessary to explore and discuss the failure of the furnace tube material to ensure its safe operation.In this paper,one of the hydrogen manufacturing converted furnace tubes which has failed in service for some time under the high temperature and the high pressure and another new tube,both of which material is HP40 Nb,are taken as research object.And,the fracture mechanical property and the injury mechanism of these tubes are studied by methods of the combination of material test and NDT(non-destructive testing)and FEM(finite element method)based on the basic theory of fracture mechanics to discuss the primary cause of fracture failure of high temperature furnace tube in actual engineering.The main work includes the following points:(1)In the ultrasonic testing experiment,the severe creep damage is occurred in the furnace tube after service.The testing result is B level,and at the same time,it is found that the creep damage strength of the tube has a certain dispersion.(2)According to conduct metallographic test on both serviced and non-serviced furnace tube,it is found that microstructures of high temperature furnace tube has changed after service: the secondary carbides separated out in body become thicker and its quantity increase near the grain boundary.(3)According to conduct the fracture toughness test on both serviced and non-serviced furnace tube,it is arrived that,after service,the fracture toughness of tube is significantly reduced.(4)According to conduct the fatigue crack propagation test on both serviced and non-serviced furnace tube,it is concluded that,after service,the ability to resist crack propagation of furnace tube is reduced,and the fatigue crack growth life is also significantly reduced.(5)Based on the microstructure characteristics of the furnace tube material,finite element modeling is performed for different elastic moduli on grain and grain boundary,then the stress and strain conditions of the material under load are discussed.The analysis shows that due to the uncoordinated deformation of the material,stress concentration occurs in some parts of the grain,and the stress concentration changes with the change of the elastic modulus,grain size,and grain boundary width.(6)Based on the finite element analysis method proposed in this paper,the stress and strain change trends of the material are discussed for cyclic load and temperature load,and then the damage mechanism of the furnace tube during furnace service is studied.