This is the value which allows the user to obtain in the calculation as an external pressure the value equal to the overpressure minus the internal pressure of the vessel.
Overpressure = 50 MPa; Internal pressure of the vessel = 2.5 MPa
then External pressure used for blast = 47.5 MPa (50 – 2.5)
Load Combinations in AutoPIPE Vessel
Bentley AutoPIPE Vessel