EmnaFati,
Your question sounds a lot like a School home work assignment.
- Why are you trying to design your own Flanges?
- Don't you know that Flanges of all sizes and pressure ratings are already available on the market?
- Don't you know that all of the dimensional data for these Flanges (and the matching Bolts) is available on the internet?
- Don't you know that your Flange must match up to other flanged objects (Valves, Strainers, Pumps, Filters, Vessel Nozzles, Instruments, etc) that already come with the industry standard Flanges?
- Don't you know the designing and using custom flanges on a system will raise the cost of the project?
Sometimes its possible to do all the right things and still get bad results