Before that I created a node set (of 792 node for each surface) of the single surfaces.
What I’m not sure is if I have to divide the Magnitude for the total node on the face (in this case 5.97 MPa / 792 node or if I have to leave the calculated value (5.97 MPa).
If I try to use the 5.97MPa the result is not realistic.
I checked it now. You have a hydrostatic pressure and a rigid body constraint (with a point spring at its reference node) applied to the same faces.
From Abaqus documentation:
A rigid body is a collection of nodes, elements, or surfaces whose motion is governed by the motion of a single node, called the rigid body reference node. The relative positions of the nodes and elements that are part of the rigid body remain constant throughout a simulation. Therefore, the constituent elements do not deform but can undergo large rigid body motions.
So it doesn’t make sense to apply loads directly to the surface with a rigid body constraint (you could just prescribe a force or moment to the reference node so that it’s transferred to the model via the selected face, which is made rigid in the process).
If you really need some springs (usually soft) on that face, you can use the Surface spring constraint instead.
Rigid body constraints or BCs applied to edges of solid models are risky too - you will get large stress concentrations.
