Creating a dummy shell will all you to analyze a single shell to up to 3 different design conditions. To create one you start by creating a horizontal vessel with saddles from the templates.
The specified vessel code does not matter so much but we will need to input a design pressure and design temperature:
Be sure to click through all the tabs of the Vessel Properties dialog and not to forget to assign materials for the vessel.
You should get a vessel similar to the one shown below:
You can delete the saddles for the purpose of this demonstration.
Click on the shell and then right click to select the “Split Shell” command and split the shell into the following lengths:
Select the middle shell and change the length to zero and remove the checkbox for “Pressure Bearing” which creates the “dummy shell”.
You can now go back to the vessel properties dialog to insert your extra shell design properties for the “second” chamber:
Something to keep in mind with this dummy shell is it creates a line of support for consideration in designing for external pressures. If you are designing for external pressures and need this dummy shell, you will need to insert a stiffener on the split of the shell to accurately take into account this line of support.