Full diameter tubesheet vs single support tubesheet 3

[Sebra]

Can anyone help me to understand what are the advantagous of having a full diameter ( same diameter as girth flange with through bolts) tubesheet to single support tubesheet in a shell and tube heat exchanger? I am reviewing the design for AXU heat echanger and the vendor used single support tubesheet.
The design pressure 46bar on tube side and 25 bar on shell side.

 

[GenB]

I see added strength in a full diameter TS due to the extended O.D.
some Mfrs use full dia. as they purchase B16 Blinds which is not longer allowed in ASME VIII1 work so now the smaller dia. is less expensive to make.

 

[Duwe6]

Further, the thru-bolts give a guide for alignment of the head & divider plate to the receiving groove in the tubesheet. It is a little harder on the maintenance crew to properly 'stuff' a cleaned tube bundle, and get it rotated to the correct position with a smooth, small tubesheet. Large, easy to see in dim light, alignment marks on the shell flange and the tubesheet make this easier to get right. But trying to roll a smooth tubesheet and the attached bundle into exact alignment is tough.

If it were mine, and the bundle would require pulling annually or more often, a thru-bolted tubesheet makes more sense. Every hour you can save during a shut-down is precious. If not thru-bolted, then weld some 'ears' onto the rim of that smooth tubesheet, to give some purchase for the pry-bar being used for final alignment.

 

[marty007]

Another benefit of bolted-through tubesheets is the ease of performing partial hydrotesting. You can connect either just the shell or just the channel to perform a partial hydrotest. For some exchangers this can make it a lot easier to detect bad tube-tubesheet joints before stuffing the bundle in the shell. Otherwise you need a separate split ring to perform a partial hydrotest.

 

[SnTMan]

What marty007 said is correct. Full diameter tubesheeets are commonly found on only a few types of exchangers:

1) Where either shell or channel is integral with the tubesheet. C-type channels or fixed tubesheet exchangers. The non-integral component bolts to the tubesheet. A removable cover typically provides access to the tubefield for maintenance or pressure testing.

2) A removable-bundle exchanger with integral channel cover, or B-type head. In this case, as marty007 says, the bundle can be hydro'd either side. Also, the tubesheet bolting flange can incorporate a means to keep the shell gasket seated when the channel is removed for access to the tubefield. Either by tapped holes or collar studs in the tubesheet.

3) Removable bundle, vertical exchangers with stationary channel down, to retain the bundle if the channel is removed.

In any case the tubesheet bolting flange should be designed for hydro. See API 660 7.6.2.4 for example.

Full diameter tubesheets are really rare on exchangers with removable bundle AND removable channel covers, that is, A-type heads. If you want one on this type exchanger, better specifiy it.

Regards,

Mike