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Can I remove pass partition plates from BEU exchanger?
4

Can I remove pass partition plates from BEU exchanger?

Can I remove pass partition plates from BEU exchanger?

(OP)
Similar to past thread:

thread794-130021: HX Modification

We have a small (14" OD x 12'-0") BEU exchanger, original design for hot glycol (tubes) to butane vaporization (shell). It was originally laid out with a vertical Pass Partition plate down the center of the tube sheet with two horizontal Pass Partition plates, one on the upper left quadrant and one on the lower left quadrant, thereby resulting in a six-pass unit. It turns out, as my luck would have it, that by removing the two horizontal pass partition plates it can be converted to a two pass unit with the U-tubes (horizontal) straddling the remaining vertical Pass Partition plate. Thus modified, the surface area and predicted thermal performance of the unit are almost exactly what we require for a new unit being requisitioned for service as a treater emulsion feed preheater.

Client would like to reuse this unit, modified as described. From past threads, I gather that this is an alteration because the fluid service changes and the construction configuration changes. Apart from that, is there any other pitfalls that we need to be wary about that would render this suggestion impractical from either a Code or Regulatory perspective? In any event, if we go down this path, the original manufacturer would be consulted, not for endorsement but more for guidance or re-modeling it for thermal performance in the modified state.

Understand that I hate this whole "used equipment" game that everyone always seems to want to play, but I am old fashioned.

RE: Can I remove pass partition plates from BEU exchanger?

(OP)
Make that second horizontal pass partition plate in the lower right quadrant...

RE: Can I remove pass partition plates from BEU exchanger?

There is nothing wrong with your idea and as long as you worked it out on the HTRI or similar, it should work. I wouldn't worry too much of the manufacturer assessment, since the thermal design you will use is different from the old one. Obviously, you include the thinning of the heat transfer areas due to the corrosion, if any recorded. The only thing a bit sketchy is your description of the ASME design as a pressure vessel. I assume that you can take care of the API 579 requirements if applicable. BTW, it takes an old fashioned to have the guts for a job like that...
Cheers,
gr2vessels

RE: Can I remove pass partition plates from BEU exchanger?

(OP)
gr2vessels,

Thanks for the reply. I will consult with our local B&PV Authority to see what documentation would be required in support of such an alteration. Where I am at (Alberta Canada) I am not sure if API-579 would be a governing document unless invoked by the B&PV Codes (ASME VIII and CSA B51). We ran Aspen Plus in both the design mode and the check-rating mode to evaluate the thermal performance of the unit based on the vendor drawings that we had for GA, bundle, tubesheet, baffles, nozzles and materials, and on that basis it seems to be a good fit in the modified condition for the new service. (I also did a few quick and dirty hand calculations that supported the computer simulation's results.) What we do not have, though, is the software that would enable prediction of tube vibration or certain other things that the OEM woulc be able to assess; so with that in mind, engaging the OEM serves as a good cross-check of our intent.

I suppose it would be prudent to have a calculation on file that verifies that removal of the two horizontal pass partition plates has not weakened the full diameter vertical pass partition plate, since the tubeside differential will now be applied fully across that plate, but in light of the small shell diameter and the plate thicknesses involved, as well as the relatively low tube side pressure drop once modified, I expect no issues.

We'll have to take a pair of scissors to the gasket...

RE: Can I remove pass partition plates from BEU exchanger?

Check the Code Calc's; if the "Pass Plates" flow divider plates are not included in the strength calculations [usually are not], they are a non-Code mechanical appurtanance, welded to the pressure boundary - the Channel Head.

If this is the case, you can indeed remove Pass Plates without it being a Code Alteration - no "R" or "U" stamp required. Just make exceptionally careful not to nick the pressure boundary. The U-stamp really stands for "U can't touch this".

The safest method is to cut the plate-to-weld junction, and stay off the weld. No chance of nicking the Pressure Boundary this way. Not enough flow disturbance caused by the weld(s) that are left inslde the Channel Head to be significant in heat transfer.

RE: Can I remove pass partition plates from BEU exchanger?

I would ask some external help to run an evaluation for this application on the HTRI (it includes the tube vibration report).
Cheers,
gr2vessels

RE: Can I remove pass partition plates from BEU exchanger?

I agree with Duwe6 in that as long as you don't touch the 'pressure boundary' parts, what you do inside is not the business of the code jurisdictional authority. I also agree with gr2vessels that you need to check the modification out thermally thoroughly (or is it thoroughly thermally) before casting this one in stone.

Look at it this way. If you were going to start with a 'clean sheet of paper' design, would the design you came up with look anything like what your modified BEM will look like after you carve on it?

If so, charge ahead. If not, procede with caution.

rmw

RE: Can I remove pass partition plates from BEU exchanger?

SNORGY, all good advice there, I would like to add one thing:

IF your passplates are gasketed into grooves in the tubesheet then removing them entirely may expose the grooves to corrosion when such allowance has not been added to the TS thickness. If this is the case, you might just cut holes in the plates you want to remove, leaving a kind of rib at the TS, and using the gasket as is.

Regards,

Mike

RE: Can I remove pass partition plates from BEU exchanger?

(OP)
Thanks all.

SnTman, thanks for that. I had not even thought of the gasket + grooves issue. I did think about holes in the PP plates just to preserve the original gasket pattern, but because the two PP plates were off the centreline I was concerned about the flow imbalance through the tubes. I have a pump on the tubeside (PC pump), so if I make the holes big enough it might not be ideal but it could be OK. Neither the run-down temperature to storage nor the off-loading of duty at the treater are critical, so the exchanger is just an optimization.

RE: Can I remove pass partition plates from BEU exchanger?

SNORGY, yeah, well it took me from yesterday to today:)

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