Bolt Torque of Heat Exchanger

[BobbyHao]

Hey all

i'm having problems with calculating the bolt torque of my heat ex-changer.
The HX has a circular end plate and gasket.
there are 20 M12 bolts in circular pattern near the edge of the end plate and a M24 at the center.
The problem is that if i tighten the M12 bolts first evenly to a certain torque, they will get loose after the center one had been tightened.
anyone knows how to calculate the bolt torque for this case?

Thanks

 

[desertfox]

Hi

I would calculate the torque required for the center bolt first based on the pressure or forces that you haven't supplied in your post and then proceed to tighten the outer bolts in a star pattern.

 

[tbuelna]

How do you know the flange bolts will lose an unacceptable amount of preload when the center bolt is tightened? Can you provide a sketch of your connection?

If there is a large difference in the structural stiffness between the M12 bolt flange connection and the M24 bolt connection thru the center, there may or may not be a significant effect from installing the M24 bolt. It seems to me that the purpose of the M24 bolt might be to handle the pressure forces in the manifold, while the M12 bolts are intended to maintain clamping pressure on the gasket.