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