Metal to metal flanges

[KN25]

How to calculate the seating loads in case of a direct metal to metal flanges?

I have a rectangular flat face flange with a rectangular flat face blind. There is no gasket in between the flanges. I am trying to calculate the total bolting loads.

Thanks for the help!

 

[gr2vessels]

KN25,
If there is no sealing required between flanges, what seating loads would you like to calculate? Do you intend to keep some pressure inside or are there ather mechanical loads on the flanged joint?
Are you trying to size a square flange with a bolted cover, but no pressure to contain?
Try to give as many as possible details of what you are trying to do, so you can get a meaningful answer.
Cheers,
gr2vessels

 

[KN25]

I am trying to blind a rectangular flange to seal a pressurized fluid.
There won't be a gasket in between the flange and the blind. My surface finish is 16 micro inch.
I have calculated the static load based on the fluid design pressure.
I wonder how to calculate the seating load as I don't have a gasket. Since I have metal to metal contact should I treat it like I have a metal gasket and used the "Y" value of that ?
Thanks.

 

[adamuk]

Good luck getting a seal. Slight variations in surface profile will require a high bolt load to seal up and this should form the basis for your calculations. Pressure sealing metal to metal joints usually use a softer metal ring with a small contact area so you don't need a massive contact force to deform the components together.

Hope this helps.

Adam Potter MEng CEng MIMechE

http://www.ax-ea.co.uk

 

[SnTMan]

KN25, assuming a gasket sealer or something, you only need enough bolting to contain the hydrostatic end force, m = 0, y = 0.

If you are trying to achieve a metal-to-metal seal you will have to get the flange material to yield, y = at least the yield point of the flange material, m reflects your confidence in maintaining a seal at operating conditons. Confident = low m, not confident = high m.

Regards,

Mike

 

[MJCronin]

Why on earth would you design a flanged joint without a gasket ?

As stated above, it will not seal !!

 

[KN25]

Thanks for the reply.
The existing design came with gasket, operating condition changed so we have to design a new rectangular blind flange.
The liquid is very viscous, so hopefully it won't leak.

 

[KN25]

I meant to say that existing design came without a gasket.
it is a 12" x 2.5" rectangular flat flange with 2 x 10mm holes in the middle.

The blind cover will only see the design pressure through the 2 x 10mm holes.

it is a bit of a unique design.

 

[EngAddict]

"The blind cover will only see the design pressure through the 2 x 10mm holes."

So it doesn't need to seal then?

Why not refine the design and add a o-ring groove? You can get it made to suit the rectangle. Then you wont need to worry about seating stress. It will make things a lot less problematic. Even a flexible graphite sheet would be better..

 

[europipe]

Maybe it´s designed to use liquid gasket seal.

 

[doct9960]

europipe,
yup, most probably a silicone sealant. They are sometimes used on compressors...

http://www2.ing.unipi.it/~a011216/Pubblicazioni/Articoli/2009_3.pdf

KN25,
The only way to analyze your rectangular flange is by FEA.

 

[KN25]

The Y value for seating load is too big for the two m16 bolts that i have.
i only have 2 m16 bolts to keep the flage tight, and they fail when it comes to seatign loads.