TEMA Floating Head / Tubesheet: Is the tube bundle cantilevered or supported at rear end?

[plantprowler]

I was studying the various TEMA HEX options that have a floating tubesheet at the rear (e.g. Types P / S / T / W) and one fundamental that confuses me is whether the entire tube bundle weight is only supported at one end i.e the fixed tubesheet end?

Or is some sort of support provided at the floating end too?

The weight of a long tube bundle + liq. inside tubes & dynamic flow loads must be quite a lot for it to be self supported by the tubes alone, correct? Eventually these loads / moments must be transmitted to the shell somehow & thence to the supports?

 

[EdStainless]

The floating head is fully supported, it is just allowed to move longitudinally.
And in reality after a few years in service most of them don't move much at all (I have seen the distorted tube bundles to prove it).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[plantprowler]

@Ed

Can you explain a bit more about how the floating tubesheet is supported?


e.g. In the drawings or event the 3D assembly videos I've seen it looks like the bundle is longitudnally and radially free to move at the read end.


Link to Video of a Floating Tube HEX

 

[racookpe1978]

Those eight floating tubesheets (part nbr 28) in the CFU cross-section simply "skid" or "get pushed sideways" away from the fixed tubesheet (part nbr 6) as the fluid in the tubes heats up. But, as noted above, they often stick and get frozen in one place because of corrosion, debris, dirt, or gunk and the tubes end up carrying the expansion forces anyway.

 

[plantprowler]

@racookpe

Part #28 looks like the baffles to me.

Isn't Part #15 the floating tubesheet?

 

[racookpe1978]

Nbr 15 is on the lowest section view of "AES" ... But I don't know its mechanical details as it heats up/cools down..

You're right, Nbr 28 are the baffles in the second view. There, the tubes are not restrained.

 

[georgeverghese]

The general trend is to avoid a S type floating head, given the probability of packing leaks which may result in loss of segregation between tubeside and shellside fluids. The more expensive T type floating head head is preferred for this reason, especially for high diff pressure applications.

 

[Afox88]

I think you are mixing up the S with the P and W which have packing. S has the same type of gaskets as a T, except without a through bolted tubesheet.

 

[georgeverghese]

Okay, got that, was recalling from memory of designs I worked on >20years ago. Thanks.

In either a T or S floating head case, an shellside expansion joint or some kind of packing on the tubeside exit nozzle is required for a 1 tubeside pass arrangement ?

 

[Afox88]

That is correct. I usually go with the expansion on the exit nozzle itself.

 

[plantprowler]

In the one tube pass arrangement with an expansion bellows on tubeside exit nozzle, there I can understand how the floating tubesheet gets support at the rear end.

The cases that confuse me are the floating tubesheets with even number of tubeside passes. In those it almost seems to me from the sketches that the rear tubesheet is hanging cantilevered from the fixed tubesheet via the tube bundle.

That's the arrangement I'm confused about in the context of how the floating tubesheet gets supported.

 

[georgeverghese]

Though I dont have the answer for this, for even tube side passes, you wouldnt need a floating head anyway - a TEMA U bundle would do very well.

 

[plantprowler]

A TEMA U-bundle cannot be rodded, correct? In severe fouling / plugging duties a TEMA U-bundle won't be recommended, I think.

 

[georgeverghese]

Believe it can - design guidelines I've read years ago have left me with the impression there are hydraulically powered cleaning tools for ID cleaning of U tube bundles - some one may confirm.

 

[Christine74]

On floating head exchangers (TEMA types "T" and "S"), the last baffle is normally somewhat thicker and acts as the floating head support.

-Christine

 

[georgeverghese]

Abstract from page 11-39 - Perry 7th edn
-----------------------------------------------
The U-tube design offers the advantage of reducing the number of
joints. In high-pressure construction this feature becomes of considerable
importance in reducing both initial and maintenance costs. The
use of U-tube construction has increased significantly with the development
of hydraulic tube cleaners, which can remove fouling residues
from both the straight and the U-bend portions of the tubes.
Mechanical cleaning of the inside of the tubes was described by
John [Chem. Eng., 66, 187–192 (Dec. 14, 1959)]. Rods and conventional
mechanical tube cleaners cannot pass from one end of the U
tube to the other. Power-driven tube cleaners, which can clean both
the straight legs of the tubes and the bends, are available
------------------------------------------------------

 

[plantprowler]

On floating head exchangers (TEMA types "T" and "S") the last baffle is normally somewhat thicker and acts the floating head support.

Ah! Now we are getting somewhere! Thanks.

But for the baffle to support the bundle weight:
[ol a]
[li]Are the tubes actually touching the baffle hole sides to transfer loads[/li]
[li]Does the bottom end of the baffle physically touch the shell to transfer loads? If it does then won't the baffle stick when sliding the tube bundle in and out of the shell?[/li]
[/ol]

 

[Afox88]

The usual goal is to make the baffle as tight as possible with the inside of the shell so that their is little to no bypass around the baffle. We also need to make sure that we can get the bundle into and out of the shell. That being said, yes the baffle will physically touch the bottom of the shell, yes it can stick to the shell when sliding the bundle and yes, the tubes will physically touch the baffles.