Research On Modification Of Stress Categorization Method In Design By Analysis Of Pressure Vessel Design

Since introduced into USA code ASME VIII-2 in 1965,Design By Analysis(DBA)method in pressure vessel had been adopted in design code of many countries in the word,because DBA method could solve many problems that Design By Formula(DBF)could not solve.In China,the first DBA code called JB4732 was published in 1995.With the development and improvement in past years,especially after stress linearization was method developed by W C Kroen to solve the incompatibility between stress field calculated by finite element method and stress categorization,DBA method had become the most popular design method,which was the most familiar by the vast engineers in pressure vessels.However,as the pressure equipment became increasingly large and complex,some problems were found and not been settled yet in the engineering application of stress categorization method.This paper aimed at the following problems found in stress categorization:(1)the linearization of some component stresses would violate the boundary conditions of surface loads of vessel and(2)the application of stress categorization in certain stress assessment regions(e.g.gross structural discontinuities regions)was difficult.The specified solution of both of problem(1)and(2)above would be proposed in this paper.The solution of problem(1)was described as follow: only hoop stress component and meridional stress component was linearized,other stress components used their real stress values(total stresses)instead of linearized stresses to take part in the computation of equivalent membrane plus bending stress together with linearized hoop stress and meridional stress.This modified stress linearization method did not violate merely but also avoided the inaccuracy resulted from linearizing certain stress components in some cases.To solve the problem(2),a new method(called DBA-L method)based on elastic analysis and lower bound of limit load theory was proposed,which was no need to categorize the stresses.Some conclusions were drawn that DBA-L method could avoid the stress categorization and potentially yielded a more ideal result than stress categorization method in some structural discontinuities.In addition,a reliability assessment study was done to assess a few design methods in pressure vessels when some design parameters as variables were considered.The conclusions were that the stability and reliability of design results of different design methods were different when the same variables were considered,which could provide a good judgement and suggestion about choose which method to use in design.