Material selection for flange fittings of equipment

The flange thickness ratio calculated by 35CrMoA studs for type a equipment flange shall be thicker than the flange thickness calculated with 20 material studs. What is the reason?
2017-07-03 Reply
35CrMoA allowable stress is greater than 20 allowable stress, preload comparison
2017-07-03 09:19:32 Reply