High Temperature And High Pressure Equipment Trapezoidal Groove Seal Failure Analysis And Research

This paper is mainly to the research about flange cracking defect on a heat exchanger of YanChang Petroleum(group) refining&Petrochemical company, finds out the reasons why the heat exchanger’s flange crack, and puts forward the countermeasures so as to prevent the similar flange crack and failure to happen again.The cracked welding neck flange’s inner diameter is Φ1200mm, the outer diameter is Φ1495mm, the kind of seal grooves is trapezoid trough, the material is16MnR, sealing gaskets is the octagonal ring. Though the Penetrant testing, find out the creak in the seal groove from the inner wall30-36mm, the most width of crack is3-4mm. Crack distribution complete turn seal grooves. The Ultrasonic testing show that the crack is most deep about150mm (crack length is about3600mm);. From the test results can be concluded that the flange crack almost throughout the flange thickness, belongs to the serious crack failure.Flange failure analysis related to the original design, flange manufacture, the usage environment, the raw materials used in supply and manufacturing, and many other factors. In order to know the causes of flange failure, this paper research from the above aspects one by one, analysis the detail of each factor, pay attention to identify the cause of the failure. To evaluate the material chemical composition, elastic modulus, yield strength, tensile strength, impact toughness, fracture toughness, fatigue, hardness and so on, through the metallographic analysis, from the micro perspective to judgment the properties of the material. With making the metal lographic sample, observe the material whether existence shrinkage, loose, segregation, different metal impurity, crack, white point, internal bubble defects, etc. Through the high magnification detection, test the material microstructure and predict the material whether contain oxidation, decarburization. corrosion, wear away, and the path of crack and so on. Through making the samples about tension test, impulse test, torsion test, fatigue test, hardness test., and determine the mechanical properties of the material. Also through the fracture analysis, corrosion analysis, and comprehensive test to determine the causes of the failure of the flange.Through the flange design theory, and calculate the flange’s force on the preloaded condition and working condition, and through the flange’s strength calibration to calculate the related stress of flange. Flange strength calibration mainly through calculating the axial bending stress σz between the flange neck and flange joint, the flange ring radial stress σr, and the flange ring shear stress σt. Then compare the σz σr、σt, with the flange’s design temperature allowable stress [σ]ft.By using the finite element analysis method, construct the flange model, mesh the model, apply loads, confirming boundary conditions, and solve the model. To get the flange equivalent stress and strain under the preloaded condition and working condition, find out the position where the biggest stress and strain appearing, combine with the mechanical properties of the material, looking for the reason of the flange crack and Invalidation.