Stress Analysis And Strength Evaluation Of Dished Tubesheet Structure

As a new type of non-standard flexible structure,the dished tubesheet is widely used in high-temperature heat exchange equipment because of its convenient manufacturing,excellent load-bearing performance and uniform temperature distribution.In this thesis,finite element method is applied to analyze stress distribution and perform strength assessment of the dished tubesheet.Influences of the structural parameters on the stress distribution of the dished tubesheet were studied,and the software to build the finite element calculation process of the dished tubesheet was developed based on VB.NET.The main work is as follows.(1)Finite element models for the dished tubesheet heat exchanger were established and stress analysis was performed under different load cases.It is found that the high stress zone of the dished tubesheet was located at the periphery of the tube laying area.With the support of tubes,stress level at most tube laying area is low and the stress is uniformly distributed.At the periphery zone of the tube laying area,bending stresses are significant with the meridional and circumferential stresses on the pipe side being negative,and those on the shell side being positive.(2)Based on the elastic analysis and elastoplastic analysis,the strength of the dished tubesheet heat exchanger were investigated using the stress classification method,the limit load method and the shakedown analysis method.The results of the stress classification method show that the strength of the equipment meets the requirements.The limit load analysis shows that the allowable pressure of the pipe course is 0.36 MPa and the allowable pressure of the shell course is 0.67 MPa,both of which exceed the corresponding design pressure meaning that plastic collapse will not occur.the stability analysis shows that under the action of alternating pressure with the maximum being the allowable pressure,the equipment is in a stable state meaning that incremental collapse can be prevented.(3)Four types of tubesheets,namely dished tubesheet,spherical tubesheet,flexible thin tubesheet and flat tubesheet,were analyzed under the same loading and compared with the dished tubesheet for the stress distribution.It is found that the stress at the connection between the tubesheet and the shell as well as the periphery zone of the tube laying area of the dished tubesheet is lower than that at the other tubesheets.With increasing the thickness of the dished tubesheet,the stress values at the periphery of the tube laying area and the transition section decrease.(4)The software to build the finite element simulation of the dished tubesheet was developed based on ANSYS APDL parametric programming language and VB.NET programming technique.The elastic and elasto-plastic analysis modules are designed for the two forms of strength failure,namely integral plastic collapse and incremental plastic collapse.The software is helpful for engineering designers to use finite element method to conduct stress analysis and strength assessment of the dished tubesheet.