Sec VIII-1 UW-13(d) 1

[Konrad]

Hello,
I need some help with understanding applicability of UW-13(d). Does it apply to joints between shell and tubesheet of a heat exchanger with both tubesheets fixed and straight tubes? Should this tubesheet be treated as a stayed/supported plate, thus exempted from UW-13(d) ?
Thanks
Konrad

 

[metengr]

I believe UW-13 provides guidance for head to shell attachment welds. Specifically, UW-13 (d) applies to flat head to shell attachment where the head is not stayed. Rules for design, fabrication and inspection for shell and tube heat exchangers falls under Part UHX.

 

[Konrad]

Right, but sketches under UW-13(d) describe tubesheet-to-shell joints as well. Only they don't clarify whether the tubesheet has straight or U tubes.

Is it a good point to send a request for interpretation?
Konrad

 

[SnTMan]

Konrad, it is common practice in shell & tube exchangers to apply UW-13(d)&(e) to the welded joint between a tubesheet and cylinder. The point here is to establish the weld dimensions. It is not common to consider the tubesheet as stayed, in my experience.

Until recently, if memory serves, there used to be a statement in UW-13(e) that a tubesheet or head could be considered stayed if 80% of the pressure loads were carried by tubes, braces or stays. Rather than try to prove this point, it was simpler to just design the weld joint per UW-13.

At that time also, the 3X criteria applied to tubesheets with a bolting flange rather than just ring flanges I believe. It was fairly common to ignore the 3X criteria and use the 2X criteria to avoid the warpage to the tubesheet caused by the large welds. Anyway, that's what I heard

Regards,

Mike

 

[Konrad]

SnTMan, Problem arise when the heat exchanger is very small. Both tubesheet and shell wall get melted thru their entire thickness and A+B requirement for shape of a line of fusion is extremely impractical to meet. And it's impossible to meet it with EBW, LBW or FW methods. That's why I'm beginning to think of demonstrating nonapplicability of UW13(d).
Thank you for the hint about 80% of load carried by tubes.
Konrad

 

[metengr]

Konrad;
Did you review Part UG-34? Continue reading Part UW-13 to (e) because you are dealing with a pressure part (tubesheet) that is being welded to a shell to form a corner joint. I believe this applies to your situation and refers you back to Figure 13.2.

 

[SnTMan]

Konrad, FYI, by concidence today I ran across the same lanquage about 80%.... in UG-93(d)(3)

Regards,

Mike

 

[deanc]

metengr has given you the right info.,you are off track and due for problems.

The 80% is gone from UW-13 because it addressed by UHX and this is not optional. You must address items per UW-13,UHX,and UG-34.

Suggest you visit with your AIA.

SnTMan: UG-93 deals with NDE---this must be tied in with UHX. Sounds good-but you cannot pick and choose.

 

[Konrad]

deanc, right UHX has provisions. But scope of applicability of UHX is pretty narrow. As a matter of fact, none of my designs fits in this scope. If UHX is not applicable, would you say that UW-13(d) is applicable in all cases?
Konrad

 

[SnTMan]

deanc, not picking and choosing, just pointing out that the lanquage still exists.

Regards,

Mike

 

[deanc]

Konrad:

I have not seen your design so I really have no opinion. All the paragraphs in the book are applicable. It is up to the designer/Eng. as to which apply. Have you spoken with your AIA?

SnTMan: No offense,but I have seen it happen too many times.
So,I am a bit gun shy.

Just remember you must address "all" of the requirements. Please review U-2 (b thru g) talk to your AIA.

 

[SnTMan]

deanc, none taken, you are right...

 

[Konrad]

Deanc, yes, I started this topic to get some opinions while in a debate with AI. The tubesheets are rectangular, welded to nonpressure enclosure on one side, and to pressurised headers of semicircular section (sort of economizer). Other designs are various, but do not fall into UHX-10. On the other hand, reading UHX-10(a) "The tubesheet shall be flat and circular"- one might say that a rectangular tubesheet is forbidden in SecVIII-1.
Konrad

 

[deanc]

Konard:

Please review U-2(g). There are exemptions in UHX if it does not fit.

Not wise to argue with the AI---see U-2(e). He may be trying to keep you out of trouble. Instead of arguing a point why not ask for some help from the same. Could even kick it up the ladder.

Can you design per TEMA? May be OK if you address all the Code requirements. You could even go with UG-101.
Guess the point I am trying to make is you must justify your design in an acceptable manner.

 

[Konrad]

Deanc, I'm not arguing to the AI. We are trying to find the best way out, he's trying to help! But if requirements of UW-13(d) are applied to a tubesheet with straight tubes- he cannot accept our design. My view is it's not applicable. Beacause of so many reasons! His view is conservative, he needs strong arguments. Stronger ones than I have. Otherwise I can redesign, but I won't be able to switch it back in the future if I would have to for some reason. And I won't be able to use laser welding, because it's never going to meet A+B size requirement!
U-2(g) doesn't explain what kind of construction is covered, and what is not. Neither U-2(e)
Can I design per TEMA? I can design it per whatever methods people made, but the uncertainity of some BPVC rules' applicability still is an issue.
Konrad
PS. I'm preparing a request for interpretation.

 

[deanc]

Konrad

It is my opinion that you could indeed use TEMA or for that matter any other design standard. IF! the ASME Code does not address your particular design and you cover any requiremnets that do. That is what U-2(g) is for.

Be careful---ask your AI that his Supv.or Eng.Group give an opinion. CYA you know.

Interpretation: Yes,it will take a while and you may not get the answer you want. There is likely one out there that already covers it.

 

[SnTMan]

Konrad, I doubt you are going to find any help in TEMA on your weld joint. TEMA mostly addresses things the Code does not already address and that are particlar to shell & tubes heat exchangers. TEMA does not address non-circular tubesheets.

You may find help in other standards. Maybe ASME Section 1 has something applicable, I'm not that familiar with it, boilers are all different shapes.

Regards,

Mike

 

[Konrad]

Yes, I don't have a problem of finding some rules. The tubesheets nor tubes are not circular, and the pitch is not triangle. But I did a FEA, I validated it by measuring distortions, and I feel good about it. The issue is whether tubesheet is supported or not. IE whether it falls within UW-13(d) or not. I calculated stiffness. It will handle more load than it takes to lift the building which I am in now. I'm not afraid of flexibility of the tubesheet. The joint will not crack due to fatigue. Material is 3mm austenitic, it will not divide into layers. The joint does not even have a contact with aggresive media. What else do I need to make sure that it's OK?
Konrad

 

[deanc]

Remember even if your pull out values are good the tubes may still act like springs and not give you any real support.

The 80% support statement is gone----Do you have stays or attached head or cover with ribs to stiffen the sheet?

Think if it was me I would consider it non-supported and move on. Read UW-13 part by part and if it does not apply your FEA may be acceptable(If the AI will buy it).

To really give an opinion on this,would need to see prints.