Benchmarking Analysis Of Stress Engineering Algorithm For Pressure Vessel Openings

Pressure vessels often work under harsh environmental conditions such as high temperature,high pressure and corrosion.Local stress concentrations is easy to be produced at its opening nozzles.If the possible excessive local stress can not be foreseen in design,the fatigue crack is easy to occur at the nozzle opening during the operation of the pressure vessel.And eventually lead to equipment failure,causing significant personnel,equipment,environmental safety and other accidents.The local stress engineering algorithm for the opening of the pressure vessel includes: American Welding Association(WRC)proposed WRC107 bulletin,WRC297 Bulletin,EN13445 standard with PED and finite element method.In practice,these algorithms have their own advantages and disadvantages.In order to calculate the local stress reasonably,safely and economically,the engineering algorithm needs to be benchmarked.The standard calculation model of tube joint is established,and the ANSYS 17.2 and NozzlePro software are used as the carrier of finite element method to calculate the local stress.On the basis of the above standard calculation model,WRC107,WRC297,EN13445 were used to calculate the local stress respectively.The results were compared with the benchmarks.Conclusions are as follows:(1)the local stress at the pressure vessel opening which calculated by the finite element method can be used as the engineering algorithm benchmark.(2)The variation of the wall thickness has no effect on the calculation results of WRC107 method,compared with the actual situation,there is a big deviation.In the case of internal pressure,the WRC107 method is not suitable for the local stress calculation of the pressure vessel.When the surface stress is calculated by the WRC297 method,the results are 2-3 times larger than the benchmark which is partial conservative.When the model is only subjected to the bending moment,The membrane stress in this model is basically the same,either with the WRC297 method or the finite element method.It can be considered that the WRC297 method can be appiled instead of the finite element method when only subjected to bending moment(3)In the scope of application,EN13445 is larger than WRC107 and WRC297 methods.The EN13445 method takes the ratio of the actual load and the limit load as the restrictive condition.The membrance load with the finite element method to get the stress divided by 1.5 times the allowable stress compared.Compared with load ratio and the membrance stress divided by 1.5 times allowable stress of the finite element method.The results of EN13445 safety margin is always greater than the finite element method.EN13445 can not be used as a criterion when the cylinder is subjected to shear stress or when the shaft is subjected to torque in the axial direction.(4)compared with the model of the cylinder tube with different thickness under the same load,it is found that when the thickness of the cylinder wall is thicker,the stress values calculated by the three methods are similar to those calculated by the finite element method.