Bundle Supports

[JesseJ]

Good Afternoon Everyone,

I have a question regarding bundle supports. Bundles are assembled with tie rods and spacers. Currently I use flat bar at 20 degrees from center on the bottom each side of the baffles as slide rails against the shell to keep the baffles from dragging for removable bundles. This works great in smaller diameter units at certain lengths.
We are getting into larger diameter and length units where this is not as effective. What are other good options that can be used?

Thanks,

Jess

 

[EdStainless]

Don't you have bottom rails built in as part of the baffle system?
I have seen a lot more than simple flat bars used.
Channel with cross bracing is a good start.

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P.E. Metallurgy, Plymouth Tube

 

[JesseJ]

We notch the baffles and weld in the flat bar so there is enough hanging out to prevent the baffles from scraping.

Some bundles go from 200# up to 9000# depending on the unit. So I understand that 1 system may not work across the board for all unit sizes.

What have you seen for channel with cross bracing? I have seen images of angle welded down the length of a shell, and then another incorporated into the side of the bundle to carry the bundle in and out of the shell assembly. Is this what you are referring to?

 

[EdStainless]

Angle welded into the shell and rails on the bottom of the bundle to sit on them.
The catch is that if it is a u-bend bundle then you can't fasten all of the baffles, they have to float for thermal expansion.
This is done in feedwater heaters for power plants.

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P.E. Metallurgy, Plymouth Tube

 

[SnTMan]

JesseJ, I prefer not to weld rails etc, to the shell if it can be avioded. Potential corrosion problems.

Flat bar (of perhaps larger dimensions) should work well for your larger sizes and is widely used in S & T exchangers. What you may use partly depends on the tubefield as well, if it don't fit, you don't want to use it.

Standard API 660 does not even require skid bars below 12,000 lb bundle weight.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[JesseJ]

Thanks for the reply's guys,

Yes we are talking about the rail system currently and have had the same thoughts. Our baffles are normally fixed tight with only the tubes growing etc with the thermal expansion through the baffles. So in a sense the railing would not effect that too much. 2 problems come up with railing. First being the diameter of the unit, if someone can get inside to weld it (smaller yet longer units). Second the added weld on the inside, keeping the track straight is tough when there is only a minimal gap between the baffles and shell wall.

So currently we are doing the right thing with the flat bar rails.

We were concerned with causing damage to the larger bundles when removing them. Or even on a BEW when pulling out the bundle, damage to the floating tubesheet. I am wondering if keeping the tubesheet diameter 1/2" radially smaller than the baffles on slide bars would keep it clear from impacting the shell wall, which in turn would reduce tube counts.

A thought I am working on is possibly using a Acetyl, Delrin or UHMW material notched under the baffles, to reduce friction when pulling bundles in and out.

 

[SnTMan]

JesseJ, interior access is another excellent reason to avoid attachments to the shell ID.

You are spot on with your thinking on packed floating head units, the tubesheet OD finish is critical and must not be marred. It seems like there are some informal guidelines, 1/4" for pipe size, 3/8" up to about 40" and 1/2" over that. The shell packing flange ID is reduced to give the proper gland clearance.

If you really feel you need low friction material, you might think about the bonded teflon slide plates sometimes used under exchanger supports. Then you would presumably not have to worry about attaching the plastic.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand