U-TUBE TUBESHEET

[picasa]

I was reading thru RCB-7.132 in TEMA 1999 code for HX design. It says "for U tube tubesheets, where the tubesheet is extended as a flange for bolting to heads or shells with ring type gaskets, P = Ps + Pb or Pt + Pb depending upon hte side under consideration". Just above this statement, it says "For other type of exchangers, P shall be the design pressure, shell side or tube side, corrected for vacuum when present on the opposite side, or differential pressure when specified by the purchaser"

I am trying to figure out if a tubesheet for a "BEU" type HX can be designed ONLY FOR DIFFERENTIAL PRESSURE. If I go by the above information in TEMA 1999, I guess I can not. Anybody has an opinion on this issue? Please let me know.

I guess it is not typical for a tubesheet to be designed only for the differential pressure. If it needs to be done, it can be done only with purchasers permission. But what about a BEU type heat exchanger? It looks like TEMA 1999 does not give you that option for a U-tube tubesheet.

 

[picasa]

ANY HEAT EXCHANGER EXPERTS IN THIS FORUM? PLEASE LET ME KNOW IF I NEED TO TRY A DIFFERENT FORUM.

 

[johnnymist2003]

Picasa,
refer to RCB-7.13 "The required effective tubesheet thickness for any type of heat exchanger shall be determined from the following paragraphs, for both tube side and shell side conditions, corroded or uncorroded, using whichever thickness is greater".In other words, one must check for both the shellside and tubeside conditions, and use the largest thickness.For this check, one would assume that the pressure on the side opposite to the side being checked is zero.Now in the case of a differential pressure, the side opposite to the side being checked is, by definition, not equal to zero.This effectively means that the thickness of the tubesheet has not been designed for the case where all pressure is lost on one side.It would mean that the differential pressure would always have to be maintained, even during hydrotest (except that it would be multiplied by 1.3 to ASME).The only way that you could safely design for differential pressure, is if the user of the exchanger ensured that the differential pressure was maintained-thus the statement in RCB-7.132 "...,or differential pressure when specified by the purchaser".
Hope this helps.
John

 

[skasliwal]

picasa,

First of all, beginning this year Tubesheet design per ASME Sec VIII, Div 1 - UHX has become mandatory. In other words I wouldnt even bother designing TS per TEMA.
Again, Its true that tubesheet are not typically designed for differential pressure as the thickness arrived at letting the pressure on other side be zero is always greater than the case where differential pressure is acting Unless ofcourse you are having negetive pressure on other side. This happens with you are designing for full pressure on one side and vaccum on the other side. Thus purchaser has to approve the differential pressure (positive) design as it limits the thickness with the onus on the purchaser to maintain that pressure under all conditions. Also from the pressure formulas you 've shown above, It doesnt seem you are doing differential preesure design anyway.
Thanks
sk