how i determine number of bolts on flange
You will have to tell us much more before we will be able to give you a helpful answer. Are you building something and you want help deciding how to design a particular flange? Are you asking what resources are used by engineers to design such things? Or are you asking what theory and experiment lies behind these resources?
Look at your local codes for flanges at the pressure and size that you are operating at. Alternatively go on a flange manufacturers web site they'll give you details.
pcd- 290 mm
bolt size - M12
Is it ok?
If yes then provide proper calculation with formulas
Depending on your application, it might be easier to determine what pressure rating you need and along with your flange diameter 335 mm which is around 13 inches, look for a a flange rating chart. This will tell you the size of bolts and number of bolts for that flange of that particular rating.
Otherwise, you will need a bit more information for your flange.
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