Research On Failure Analysis And Fracture Mechanism Of Stainless Steel Elbow

To be seasoned with the specification of process piping with defer structure, It is frequently to use stainless steel bending elbow for the equipment of petrochemical industry. The representative material is 18-8 stainless steel, because of the tenacity, could be used diffusely, but the elbow could give severity influence to the formal and safety operation for equipment. To solve the problem of the crack of stainless steel elbow become into the difficulty of the production elbow.This thesis reflects the fact of crack for using 18-8 elbows in a new system by the refinery of Company of Maoming Petrochemical Corporation, the topic of testing and studying has been coming in existence, to roundly analyses the reasons of the crack on the elbow, find out that the main reason is: the very low temperature of molding courses the crack of the elbow during bending, the austenitic of the pipe deformed, induced the martinsite, because of processing without solid solubility. Therefore coursed the damages of hysteresis which named "natural crack", the crack bears upon the content of hydrogen which could course the brittleness, the crack might come up within 1 ~2 days, or might come up after many month, if the medium CI content higher than normal in the piping, it might quicken the cracks coming cup.This thesis combine the other reasons of cracks on the 18-8 austenitic stainless steel elbow during the bending with failure analysistestings, the results indicated: when heat it up to bend the pipe by the force of heating press and processing pressing, the light crack come up on the surface of the pipe of the pipe, at the position of a scar which left by the mechanical processing and the crystal boundary on the oxidized surface; the temperature and the deformation volume could bring seriously influence to the deformation volume under high temperature, The testing indicated that the heating bending and temperature brings influence to the percussive tenacity of the pipe. The coarseness of the surface of the pipe could give influence to the cracking: under the same temperature, the smooth testing pipe could be deformed under more forces, or under the same deformation volume, the smooth testing pipe could be bended in higher temperature. That means: the temperature and the deformation volume should be comprehensively considered.