Nuts and Bolts - Minimum Bearing Area

If you use a nut which is not totally in contact with the flange you risk a bolt destruction due to bending moments which are extremely dangerous since threads are very sensitive to bending due to thread root stress concentration effects.

On the flange as you describe the contact pressure will NOT be uniform.

There is something called pressure cone, go through handbook. It is detailed there. Also some links are available, but are not necessary.

You can google pressure cone and get the answer.

By the way How Nut can be more than the flange face ? I simply can not imagine the concept.

I am guessing (and I stress this is purely a guess) that what he means is that the Pitch Circle Diameter (PCD) of the bolts is so large that the bearing area of the nuts overhangs the outside diameter of the flange, therefore not giving a uniform 'standard' bearing area.

Looking at it that way, it must be a non-standard flange that he is using.

Correct me if I am wrong.

Nirmal7 - I think we need some clarification on this before anyone can comment or help you further - a quick diagram might be helpful.

Kind Regards

Kev Brown