Calculation of tube stresses when lifting a heat exchanger with a thin bellows

[Tomtation]

Does anyone know of a method to check the stress in the tubes of a heat exchanger when lifting the unit from horizontal to vertical when there is a thin bellows expansion joint in the shell? I know the tubes will take the load but is there a method to determine the load on the tubes?

Thanks

Tomtation

 

[SnTMan]

Well yeah, beam type bending. I'd lock down the bellows though.

Regards,

Mike

 

[Duwe6]

Do NOT cut the 'shipping bars' on the bellows joint until your Hx is set, the pipes connected and pipe stress verified. I prefer to only cut out the center half of each bar, leaving both ends. That way, if the Hx needs moved later, some angle-iron can be easily welded across that gap, and no welding heat will reach the shell or bellows.

 

[Tomtation]

My contention is that in most cases there is no need for shipping bars on the expansion joint for lifting the unit from the horizontal position because the tubes will take the load (not the expansion joint). Please refer to the attached sample calculations and let me know what you think.

Thanks
Tomtation

 

[SnTMan]

Tomtation, ever seen one blow up?

 

[Tomtation]

No, why have you?

Someone smarter than I pointed out that my proposed method is invalid because the tubes do not act in unison to resist the shear flow due to the bending moment. So I'm back to square one.

 

[SnTMan]

Yeah, I have, bottom unit of a horizontal stack. Supports no aligned. Takes only a small eccentricity in loading or geometry of the joint to cause problems. What's the problem with shipping or maintenance braces?

Regards,

Mike

 

[Tomtation]

There is no problem adding shipping brackets but I'm just not convinced that they are required in most cases.
Thanks for your comments.

Regards

Tom

 

[SnTMan]

Tomtation, I don't generally feel that lucky

 

[racookpe1978]

Remember: The shipping brackets are only sized to prevent the bellows and the two bellow attachment rings from moving relative to one another during "normal" - ie, very, very careful - lifting, shipping and handling.

Sure, they are probably a little oversized. But those things are NOT intended to prevent the movement of the entire heat exchanger and both ends and both tubesheets (or one end and one tubesheet and all of the tubes in the bundle.)

the tube bundle, as pointed out above, will not act as a single "reinforced mass of tubes" but as a very large of loosely sliding individual tubes each contacting the loose hole in the tubesheet and spreader plates one at a time. So, the first tube hits the tube sheet hole, picks up all the weight stress (because it is the first to touch and begin resisting the bending force) and so deforms (kinks. The second touches, deforms, and kinks. The third, the fourth, etc. Eventually of course, enough tubes have kinked so the 331st is not kinked.