Everyone that I know of uses Charts for preliminary estimation. These charts can be for Pipe Thickness, Weight of Pipe, Allowable Loads and so on.
Recently I did a project in which the flange design was carried out based on ASME Section VIII Division 2. As Caesar II does not have a direct way of analyzing this, I had to export the forces and moments and then do comparison. I developed a handy chart that helped me to do a quick check of whether a particular flange design was adequate or not based on forces and Moments.
I have attached this chart for your easy reference.Maximum Allowable Flange Loads based on ASME Section VIII Division 2