Why flange faces are thicker?

[ashfaqanwer]

You may have noticed that the flange faces are much more thicker than the actual pipeline thickness.

The reason is that they have to take the gasket loading. More the gasket loading, more would be the thickness of flange faces. If they would not be that thick, they may get distorted while taking the gasket / bolting load.

All standard flanges are adequately designed to take enough of this load. But if you are designing a non-standard flange as per ASME you will see yourself in the calculations the relation between the gasket loading and flange face thickness.