What is the sealing principle of flat welded flange?

The two sealing surfaces of the flat welded flange bolts squeeze the flange gasket to form a seal, but this can also lead to seal failure. To maintain the seal, it is necessary to apply a large bolt force, which requires larger bolts. A flat welded flange is an ineffective seal because 50% of the bolt load is used to squeeze the gasket, while only the remaining 50% of the load maintains the pressure. The larger bolts need to match larger nuts, which means a larger diameter bolt is required to create the necessary conditions for tightening the nut.