Answer:
The tubesheet design conditions are set as default in Autopipe Vessel based on MAWP which may be higher than the design pressure.
Eg. observe in the image below:
In the Design Conditions tab, both for Shellside and Tubeside pressure, the MAWP is considered.
However, observe in the report that for tubeside MAWP = design pressure = 1.8 MPa, however, in the shellside, the MAWP=1.79 MPa which is higher than 1.6 MPa.
The user can replace the MAWP values in the design conditions tab by manually selecting the design pressure by double clicking on the MAWP in the grid and selecting from the dropdown as shown below:
After changing the shell side pressure condition to design pressure from MAWP, run the report and you would observe that the tubesheet design is now based not on MAWP but the design pressure (1.6 MPa):
Note: When the designer doesn’t know the maximum allowable pressure, then the program is able to determine the maximum permissible pressure. By default, this maximum permissible pressure is used as the maximum allowable pressure. But if the designer knows the maximum allowable pressure then they can input this value and the program will use this value to determine the test pressure.