1800mm Long bolts clamping flanges

[td_mech]

Hi
I am working on a stack (something like a heat exchanger stack layered with steel, graphite gasket, steel .. ) which is placed inside a heated chamber. The chamber is heated to 400°C. The stack could be up to 1800mm or even more. Bolted together between thick flanges with M40 bolts.
The tallest stack we have made today is 500mm it seals well and works. Sales want to scale up and want to know the maximum length of stack they can offer. I am trying to look for similar applications where long bolts has been used.

What crosses my mind is that there could be bolt limitations in terms of the springiness of the long bolts?

Any information would be appreciated.

Thanks in advance

 

[XL83NL]

Electrolyzers? There was a similar post here not so long ago about them, I think they also used very long studs/bolts.
Otherwise, plate heat exchangers?

 

[Compositepro]

Increasing the length does increase the "springiness" of the bolts but it does not affect the strength of the bolts or the load on the bolts. Springiness is required to compensate for thermal expansion. I don't think making them longer should be a problem. Making them shorter might be a problem.

 

[goutam_freelance]

Gasketed PHE could be similar.

 

[LittleInch]

The longer the bolt the greater the relaxation is when they expand as the sealing mechanism varies by movement.

so typically you need thigs like springs or belville washers to compensate for this bolt elongation.

Some pumps are made like this.

But more than 500mm is quite odd. Why not move to two sets of flanges once you go more than 500mm?

got a drawing or photo or even a sketch?

Pressure containment pressure?

 

[td_mech]

Sorry for the late response. I have tried to illustrate the setup in the image above. Two large flanges compresses black graphite gaskets. The green plates are sandwitch in between the massive flanges. The gasket needs a pressure of 20-80MPa to seal. We aim for a initial pressure of 40MPa. For now this has worked without belville washers, since the gasket has a sealing range. But I see that for every heating-cooling cycle we will loose some pretention in the gaskets. Because of some permanent deformation in the graphite for each cycle. The stack does not undergo thermal cycling. Only a few start and stops.

There is no mechanical steel-to-steel contact to prevent over compression of the gaskets as of today. So the compression of the stack is manually measured.

Since the number of gaskets scales up linear together with the length of the bolts, same forces going through the bolts. We use the biggest Milwaukee Impact tool that is available. The longer the threaded bars get, the more it will twist during torquing? Could that be problem? Bolt stretchers would be best, but we don't have that available yet.


I looked up the post about electrolyte crazy bolting system: link. That was interesting. Thanks

 

[Trestala]

Do you have to clamp multiple gaskets? Or can you just use a ring spacer or a spade so you only have 2 gaskets to make up for that gap?