I have calculated bolts area for a heat exchanger U type both sides gasketed with A-2 and the required is appr. 390cm2
Using 8-threads TEMA bolts ( 32 of 1"3/4) area available is 409cm2 higher than required but it restrics heat exchanger MAWP to 83barg (DP=80barg). Usually I do not have this small margin but since bolts Yiel Strenght ( for SA193B7) is much higher than the allowable of 1720bar I think the design is ok. Please let me know if there is any concern.
Another thing is that 4 of 32 bolts will be constructed as collar bolts. Can this configuration act negative to bolt effective area someway ?
I suppose manufacturer will use the same material and bolt square root and will make the collar bolt as a one piece constructor.
Finally I suppose that collar bolts during seating are attached to the tubesheet firmly and are no having any space from it, so the bolting to be done between tubesheet flanged extension and body flanges, not between the two body flanges. Since I have not heard of any standard relative to collar bolts I make the heigh of the bolting region of the bolt equal to the nuts height.Please advise

Pastyl, how are you going to do your hydro test?

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Konrad Anikiel

For A193B7 material minimum yield strength is 7250bar and during hydrotest at 115bar bolts will subject to a stress value of 2370bar which is much more less. Other pressure parts during hydrotest will face a larger stress ratio than bolts.Taking into consideration ( from Div. 2 now) that stresses values during hudrotest shall not exceed 0.9Sy and if we accept that this is valid for all the pressure parts then, the bolts during hydrotest have the lower stress ratio of all.This is the reason why I did not give to bolts area larger safety margin.
If you are asking how the hydrotest will done then it will be done in 3 steps: 1) bundle into the shell by bolting tubesheet flanged extension to the shell flange, test at shell hydrotest pressure. 2) Bundle outside shell by bolting the tubesheet to the channel flange, test at tube design pressure.3) Heat exchanger will be tested assembled at shell and tube test pressures for shell and tubes elements separately -not at once.

From what you said before it seemed that you have a very narrow margin on bolts strength. And that it is limiting the MAWP...

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Konrad Anikiel

It is not quite clear if MAWP of a vessel can be restricted for pressure parts which are not subject to primary stress, such as the bolts, but, if so, MAWP can be even lower as the DP.
MAWP is a calculated as maximum acceptable pressure,with the meaning that stresses caused from this are lower than the allowable, for all the pressure parts after corrosion have been introduced, and must be higher than DP.Then you can declare as MAWP=DP and make hydrotest at 1.33DP .
My primary question is if you really will face a problem for this safety margin since during operation bolt stresses are 1640bar and allowable is 1720bar. But these bolts have minimum yield stength 7250bar tabulated for A193B7 t<=2"1/2, from 3.1B approximately 7900bar and are quenched and tempered at 640 C , so for table 3 of sec. 2 part d are subject to annealed bolting material with stress limit =0.75Sy= 5440bar appr.