Why stresses are very high and failing in shell/channel joint when split the shell in 3 parts?
Example:
Case 1: When we use single shell with 25mm thickness, there is no error.
Case 2: When we split the shell in three parts with 25mm thickness at near both tubesheets and 20mm shell thickness at middle shell component we are getting below error.
Answer:
Note that, in case we have the different shell thicknesses in the heat exchanger then Shell axial stiffness and Shell-Tube Rigidity coefficients will change and that will affect the stresses in the integrated shell/Tubesheet as per ASME Section VIII Div.1, UHX-13.
Code Reference:
Lengths of shell of thickness t s ,1 adjacent to tubesheets :
Shell axial stiffness & Rigidity Stiffness:
Stress in the integrated shell/Tubesheet :
In Case 1 stresses are within the Allowable limit but in Case 2 stresses are exceeding the allowable limit hence you are facing the error.
To avoid the error you need to limit the stresses by changing the design parameters.
Answer:
For Case 1: You can see the stresses are exceeding the allowable in design case. Hence, we used simplified Elasto-Plasticity calculation procedure.
For Case 2: Stresses are also exceeding the allowable in design case as well as operating case. Hence, we concluded that shell/channel joint has insufficient strength.
See the code reference,