Bundles for large vertical heat exchangers 1

[merrillwalt]

Anyone have experience in determining whether a cradle is needed for lifting the bundle for a large vertical exchanger from the horizontal position to the vertical position for installation in the shell? Cradle ostensibly is needed to prevent excessive deflection of the bundle in the horizontal position.

 

[gr2vessels]

I have designed large vertical exchangers with removable bundle, but my design allowed for the removal of the bundle with the shell section together. That would catter for the lifting loads from horizontal to vertical orientation and viceversa. Otherwise, you might want to use a 'shell' section, you can store and use on the ground, for the handling of your bundle. I believe it would be cheaper than fabricating a structural cradle.
Cheers,
gr2vessels

 

[rmw]

Kind of like a shipping shell, a light weight non code shell that can be removed once the bundle is oriented vertically ready for insertion and reinserted if the bundle has to be removed from its permanent shell.

Is this insertion being done where the bundle and shell are manufactured, or at a different site.

There is a lot more that you can tell us about this bundle and/or shell before we can give a decent answer.

rmw

 

[merrillwalt]

This is a replacement bundle. The shell is in place. The bundle has 6" thick tubesheets with the tubes welded to the tubesheets. There are 230 tubes in the bundle that are 1-1/2" finned tubes. My calculations indicate that there is no real need for a cradle. There is no documentation as to why a cradle had been previously used for this bundle. Also, there are pictures of a similar bundle being removed from the shell without a cradle without excessive deflection. I am puzzled as to what criteria made someone think a cradle was required.

 

[PMSki000]

The "tailing" of the load, when lifting the bundle from horizontal to vertical could damage the tubes. Fabricators will sometimes include provisions as simple as a hole in the baffle nearest the bottom or the bundle, while others include a skid plate.
The aspect of a "mock" shell is often required for the purpose of testing the bundle, possibly more common if the HE design is for differential pressure.

 

[merrillwalt]

Still looking for some technical reason as to why a cradle would be needed that can be justified by calculations.

 

[gr2vessels]

merillwalt,
Error of judgement of an over zealous engineer might not be a very technical reason, but could be a plausible explanation.
However, from this end I cannot see how did you interpret the use of the craddle as installation aid. It could be usefull for transport purposes, including horizontal and vertical lifting, but I'm unable to see any construction engineering logic in lifting the bundle with a cradle, insert one end of the bundle in the vertical shell, bring another crane, hook up the cradle, disconnect the bundle somehow without crushing the whole installation, remove the cradle, etc...A simple task made incredibly complicated and dangerous. Is it possible that there might be an error in your interpretation?
gr2vessels

 

[saplanti]

In case your heat exchanger is part of the bundles of heat recovery steam generator or similar you may need cradle to lift it horizontal to horizontal and horizontal to vertical positions.

If you are talking about shell and tube heat exchanger gr2vessels has already given you very good advice.

Hope it helps.

Ibrahim Demir

 

[merrillwalt]

To clarify, the cradle is only used for shipping and then for lifting the bundle from the horizontal to the vertical position. What is puzzling to me is that the cradle was constructed at a cost of probably $75,000, but there is no documentation clearly showing why it would be needed. As stated earlier, my calculations show that the tubes would not be overstressed or deflect significantly when the bundle is lifted. Also, to clarify my comments about the pictures, a bundle was lifted out of the shell and rotated into the horizontal position without using a cradle and without any damage.

 

[rmw]

Lifting a bundle and rotating it (from or to) horizontal is much different than shipping the thing cross country via truck or overseas via boat. A cradle would be most advisable for those conditions.

It could then be used for rotating the bundle once it reached site.

rmw

 

[saplanti]

I have designed for the same purpose a couple of times. In one case, the intention was to replace the existing leaking bundles of entire 4 HRSGs with the new bundles. I designed one cradle ( basicly a stong back) and manufactured two for transportation all different bundles seperately and lifting them horizintal to horizontal and rotating them in the air from horizontal to vertical. In that scenario we detached the strong back leaving on the ground while the crane was still holding the bundle in the air vertically. We had to use tension hydraulic cylinders for that application.

The operator did not properly read the lifting procedure and broke one of the hydraulic cylinder and had to wait to get a new one from the US.

There are some companies do the lifting with simple cradle with wire ropes, however they do take some risks on the tube bending ( not crashing) and bouncing during the lifting and in air. Rotation and control of the bundle during the lifting and in air are not easy and require very slow operation, and still risky.

So this is the job you need to do right, and you must not take risk on the manufactures bundle. So, you are the one to make the right decision what to do and how.

Kind regards,

Ibrahim Demir

 

[saplanti]

Please forgive me for the unwanted typing mistake.
Please read "... manufactures bundle" as "....manufactured bundle" in the last pharagraph.

Kind regards,

Ibrahim Demir

 

[merrillwalt]

Maybe I need to rephrase my question to ask if anyone has done calculations to show that a cradle is REQUIRED to lift the bundle from horizontal to vertical position. Bundle in question has 3" tubes that are welded into the tubesheets and is very stiff. It's hard for me to believe a cradle is needed. Also hard to justify spending $75,000 for something that is not needed.

 

[mayda]

Every case should be looked at individually, since details will vary, but as merrillwalt has found, if you do the calculations, you will probably find in many cases that such a bundle can indeed be lifted without a cradle.

Using the parallel axis theorem, it can be found that the stiffness of the bundle is very large. So, as long as the tube to tubesheet joint is adequate to transfer the tensile loads from the lifting operation (I have not done calculations to see if there would be a combination where it would not be - I would think if the joint meets Code requirements, it will be quite strong enough for the loads during lifting and rotating from horizontal to vertical.

We have a few vertical bundles at our site, one very large, with about 7000 tubes 3/4" diameter. We have sucessfully lifted all of these bundles vertically out of the shell, rotated to horizontal, cleaned and inspected, then lifted back to vertical and reinstalled without any damage to the bundle. In no case have I calculated any need for a cradle.

Our bundles do have floating heads at the bottom end, with lugs or trunnions which are used for the tailing crane. So long as the sling is not put around the tube bundle itself, no damage will occur to the tubes.

I agree a cradle could be beneficial for shipping puroposes, but if it is not needed for lifting, then I would recommend removing it before lifting. Trying to remove it after getting the bundle to vertical could be inviting an accident.

Test shells are a completely different matter - such a shell may be very useful for leak testing once the bundle is removed from its "normal" shell, but again, unless calculations prove it is necessary for lifting, I would not use it during the lifitng operation.

 

[merrillwalt]

Mayda, many thanks!

 

[roca]

merrillwalt
Are the tubes 1.5" (see your second post) or 3" (see your 5th post?

 

[merrillwalt]

Each tube is actually a combination of 3" bare and 1-1/2" finned sections.

 

[gr2vessels]

Aha, perhaps the craddle is only needed to protect the finned tubes from damage during the handling and resting it on the laydown area!
Cheers,
gr2vessels

 

[roca]

yes - I belive that will be the reason
Fins are easily crushed
The bundle itself will be stiff enough to lift

 

[merrillwalt]

Sorry guys, it's not about the fins! There are shipping baffles that protect the fins during transit. Also, during the lifting process the sling would not contact the finned section of the tubes. I appreciate all the comments from everyone. Lots of good thoughts!