The two sealing faces of the bolt press against the flange gasket and form a seal, but this also causes the seal to break. To maintain the seal, a large bolt force has to be maintained, so the bolts have to be made larger. A bigger bolt has to fit a bigger nut, which means a bigger diameter bolt is needed to make the nut tighter. However, the larger the diameter of the bolt, the suitable flange will become bent, and the only solution is to increase the wall thickness of the flange section. The enormous size and weight required for the entire installation is a particular problem in the offshore environment, where weight is always a major concern. Furthermore, flat-welded flanges are essentially ineffective seals, requiring 50% of the bolt load to squeeze the gasket and only 50% to maintain pressure.
