A cylindrical pressure vessel can be thought of as a cylinder with both ends having a shape of hemisphere or similar curved faces. So you can first the sketch the outer half profile and then pull-rotate around its axis to generate a 3d model. Later on, you can add the openings, stand, and other relevant features. See below.
If you have access to Discovery AIM, you can download the pressure vessel example from below link and check out the model in that example.