Bonnets / bolted covers on heat exchangers

[rbel038]

Hi guys,

Since im relatively new to pressure vessel design im struggling with a concept which i wish to gather some opinions/knowledge on. Specifically in the case of heat exchangers where does the vessel end and where does the piping begin?

What bought this up is we have a shell and tube being designed that is fixed tubesheet with a concentric reducer cone on one tubeside and an eccentric reducing cone on the other. People here have differing views on whether these reducing sections are under the pipe code (b31.3) or part of the vessel (under div.1).

The reasoning they say is that the heat exchange process is only taking place between tubesheet to tubesheet so that the bonnets can be classed as piping. Id like to hear your thoughts on this.

Cheers,
Richard

 

[gr2vessels]

This is a typical NEN exchanger and the cones are part of this exchanger, like channel and bonnet. Also, the flanges welded in top of the cone are part of the exchanger, as the inlet/outlet nozzles for the tubeside. Depending on the size, you can select the cones as fittings, but they'll be designed per BPV code, just as you may select shells made of pipe.
PS. I can't see any benefit in distorting the perception of pressure vessel and design per piping code.
Cheers,
gr2vessels

 

[Karloss12]

Within the Bonnet there are lots of other factors such as fluid impingment, fluid expansion, fluid velocity, partition walls. The list goes on. Are any of these addressed in b31.3? Could any of these be an issue?

The bonnet is bolted to and exerts loads on the tubesheet. Do your piping engineers know anything about tube sheets and the fundamentals behind their design? (Just like a doubler pad welded to a pressure vessel doesn't hold pressure but remains in the pressure vessel engineers domain. Any attachments then welded to this pad is in the structual engineers domain. We don't want structual engineers welding attachments directly onto a peice of pressure equipment that they don't understand.)

At what connection do you think it is SAFEST for the equipment to go from the heat exchanger code to b31.3. At the tube sheet where a piping engineer knows little about the design of tube sheet he is bolting to or possibly doesn't understand the envronment in the bonnet? Or at the end of the reducer cone where there is a nice familiar flange for him to bolt on to?

It's all abot safety!

 

[SnTMan]

rbel038, your scope under Sec VIII, Div 1 can be found in U-1(e).

Regards,

Mike

 

[Duwe6]

To simplify the Sect VIII, Div 1 stuff; if the item was necessary [and used] for the official fabrication of the vessel, it is part of the vessel. Manway covers are routinely mistaken for 'just another flange' and folks try to use pipe codes to weld to them. Nope - integral part of the vessel.
It would be hard to find something more necessary than your heads for the exchanger. And, if you look, these heads are listed on the U-1. If it is documented on yopur U-1, it is an integral part of your vessel.

 

[rmw]

Give some thought to the term "pressure boundary".

rmw

 

[rbel038]

Thanks alot guys , taken note of the points raised from everyone here. U-1(e)(1)(c) am i interpretting this rite by saying that the first flange is the one mating to the piping system (the bolted/flanged joint being the tubesheet) at the small end of the reducer.

Yes Karloss when you take a step back and look at the stresses acting it makes sense to terminate the vessel at something familiar to the piping engineer (and im guessing easier to model in autopipe and the like)

gr2vessels, the issue is (even though i dont like it at all) B31.3 is a way for our workshop to manufacture the reducer sections (as we dont have a u-stamp but have qualified welders) and attach them to the u-stamp vessel.