UHX for Tubesheet design of Div. 2 Heat Exchanger

[BPVFEA]

We have designed exchanger with Div-2 Ed 2004 with ASME CODE STAMP requirement. Since Div-2 does not give Tubesheet thickness calculations, we had performed calculations with Div-1 UHX which is conservative approach. But the PE is insisting to do FEA becuase Div-2 does not allow anywhere to use UHX. My question is
(1) Is the PE's view correct?
(2) Why it is not accpetable though it is conservative? (3) Similarly can we use Tube-Tubesheet joint calculations as per UHX since these are not given in Div2. (But Ed 2007 Div.2 has provided these calculations same from 2004 Div.1)
If it is acceptable to use Div-1, Please tell me the relevant clause reference.
Eagerly waiting for your reply
Thank you

 

[thermmech]

You need to provide more info on your exchanger.
Did you talk with the AI in your jurisdiction on the requirements this being exchanger designed to ASME VIII-2 Ed 2004? Is the exchanger already built or is this a new design?
Why would TS calculations from Div 1 be a conservative approach?
Regarding T2TS joints - you have answered the question your self, but still you could carry out the FEA of the joints and compare the stresses/loeads with those allowable as per Code or MTRs.

 

[BPVFEA]

The HE configuration is "Tubesheet Integral With Shell and Channel" (Fig UHX-12.1.a in old div. 1)
I thought TS calculations from Div 1 be a conservative because I would be using div.1 allowable (1A) instead of Div.2 allowable.
Thank you for your comments. But I havent got clear answers to my queries.

 

[vesselguy]

BPVFEA,

I have never done a Div2 Exchanger before but I have done a few Div2 vessels so I'd just share with you my opinion from those experiences. When I design a vessel using Div. 2, the reasons are as follows in order of importance:
1. To save on pressure membrane thicknesses (thus cost) for more expensive materials, and/or
2. When there is cyclic loading or other "non-typical" loading conditions that would be best analysis with FEA. Note you can also do FEA with Div. 1 as well to "support" the design.

Hence, although is would be acceptable to design the tube sheet with UHX, if I were your client, I want you to design the TS with FEA to save me cost on what would have been a very thick (I imagine you must be in the range of 6 to 8 inchs or more) TS. Why don't to communicate with your Client on the reason and reason out a solution "together"?

 

[PVGuy]

If you are able to use the 2007 edition, 2008 Addenda of Division 2. Part 4.18 for Tubesheet design is the same design methodology as used in UHX. Obviously there may be some other differences as far as toughness, inspection, or testing requirements; but if you compare the two you will see they are the same method.

 

[BPVFEA]

I agree with you Vesselguy, but my question is more of a "DOCUMENTATION" kind. I can rephrase my question like below.

For a DIV-2 (Ed.2004) CODE STAMPED heat exchanger, do I need to submit Tubesheet FEA Report to PE if I have already submitted the Tubesheet Calculations as per UHX Div.1 ?

Is it written anywhere that UHX calculations are acceptable for Div-2 jobs?

 

[vpl]

If the PE is requiring it before s/he will sign off on the paperwork - I'd recommend going ahead and doing it. The time you spend trying to prove that what you did was ok will far exceed just doing what was asked. Especially since, in the end, you're going to have to come up with a better justification then "I went to this free website and these anoymous strangers said I was ok" (no matter how good the advice you get here.)

Patricia Lougheed

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[vesselguy]

BPVFEA,

I reread your original post and it looks like you had compeleted an HX using 2004 Edition of the Div. 2 Code, but designed the TS using UHX. Now, your client want you to give him FEA report for the TS just because it is a Div. 2 vessel. Have I got it right?

I assume you are fabricator? Yes? If so, then go back to the PO and check what was agreed upon for documentations. If it says you will supply FEA report for the tubesheet then you know what the answer is. If not, then tell him "sure, but it will cost another $35000."

I agree with you that you don not need FEA for the tube sheet if you did it with UHX as it will be conservative (safer). And as you too have pointed out that the 2007 Div. 2 has build in the choice of design by rules and included UHX. If I were you, I would argue on this basis and get your client to justify why he needs FEA. I think it comes down to lack of knowledge of what's in the Code. But if he can't give a sound technical basis for the request, then it comes down to what was written in in the PO. If its not in the PO then he don't get it.

Others may know more.

 

[BPVFEA]

Dear VPL,
After PE insisted, without waiting we have submitted the FEA. Since FEA was not in the scope of PO, customer finally paid for it.
But my intention of this post was to know what is correct.
When there are other REQUIRED FEAs in hand, I should not be doing FEA which is really NOT REQUIRED.
Anyway thank you all for your comments.

 

[Mandeep1]

The FEA of the tubesheet joint is complicated, with tube holes, boundary conditions and various loading. So, an experienced engineer who understands this is needed.

All FEA is not equal.

If you make wrong assumptions, you get wrong answers. If you have not done before, IMHO you can spend a lot of time researching the best way to model the actual problem.

Did your PE check the boundary conditions of the FE model???

Because any college graduate can do FEA and generate pretty pictures. But, does that simulate the real world is the important question.

I would still make sure the design passes with UHX.

As it is said 207 Ed. of Div. 2 gets the tubesheet design from part UHX in Div. 1.


best regards,
Mandeep Singh