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Nozzle loads consideration for Flange rating selection.

Nozzle loads consideration for Flange rating selection.

Nozzle loads consideration for Flange rating selection.

My client asks to check rating flange against Nozzle loads equivalent pressure combined with equipment design pressure.If it fails check the flange as per ASME Sec VIII div 1 appendix 2.

For establishing equivalent pressure due to Nozzle loads Kellog's formula is generally used by pressure vessel designers. However this has not come into the codes?

In my experience when a rating flange is checked as per ASME Sec VIII div 1 app 2, it generally fails since allowable stress of ASME pressure vessel code is different from ASME Piping code.

However when a particular nozzle flange fails in the above conditions, can we design the flange as per ASME Sec VIII div 1 App 2, with allowable stress as per ASME B31.3 in consideration of para 304.5.1 where it allows such method. If it still fails, there is no other option except to enhance the pressure rating of the flange.

RE: Nozzle loads consideration for Flange rating selection.

Two comments:
1) See Code Case 2901
2) Appendix 2 is an excellent method for designing flanges. It was never intended to be used to analyze existing flanges. Plus, it doesn't consider leakage.

The equivalent pressure method is not in the code because no one has requested it.

Note that if you were designing a flange on a vessel, then you would be required to use the allowable stress from the vessel code, not the piping code.

RE: Nozzle loads consideration for Flange rating selection.


Thanks TGS4 (Mechanical) for code case 2901 reference.

My question relates to Standard rating flange as per ASME B16.5 (which is governed by ASME B31.3 piping code) for nozzles on pressure vessels as permitted in UG-44 of the code without designing it to code.

The client asks to check the sufficiency of the rating pressure of such standard flange against Design pressure + Equivalent pressure from Nozzle loads. Equivalent pressure assessment will however be as per Kellog's formaula or as per ASME Code case 2901 as stated by TGS4

If it fails in above check, we may design these standard rating flanges to ASME Sec VIII div 1 APP 2 with allowable stress as per ASME B31.3 in consideration of para 304.5.1 (b) of the piping code?

If it still fails, the pressure rating of the flange is to be enhanced to next higher class to satisfy the check.

RE: Nozzle loads consideration for Flange rating selection.

If you are not getting the Code stamp, then you can do whatever you like. If you are following the Code, then follow the rules therein. Or U-2(g) if there are no rules.

RE: Nozzle loads consideration for Flange rating selection.

CC2901 is an equivalent pressure method, it just uses a more appropriate allowable limit than typically used when referring to the Kellogg formula. If it fails CC2901 you would be wasting your time designing to App2. Although, if you are only looking at the piping side of the nozzle in your scope (which it seems like you are), then I think technically the CC is only applicable to the vessel codes, even through this method is equally relevant to all pipe flanges. Maybe TGS4 knows if anyone on the B31 committees are looking to adopt this CC as part of the 'code alignment process'..

RE: Nozzle loads consideration for Flange rating selection.

Thank you TGS4 and BJI for your comments on the subject.

I found that there is a code interpretation BPV-1-16-85 referring to UG-22 loadings to be applied to Standard Nozzle flanges of UG-11 and U-44. UG-22 (loadings included external piping loads applied to standard nozzle flange loads).

See the link for the code interpretation extract.

Hence standard piping Nozzle flanges (to ASME B 16.5 / 16.47)are supposed to withstand these loads by checking rating pressure with Design pressure + Equivalent pressure from Nozzle loads (as referenced in code case 2901) as being insisted by the clients some times.

Some clients even ask for all Standard B16.5/16.47 flanges be run through an Appendix 2 analysis.

RE: Nozzle loads consideration for Flange rating selection.

Code Case 2901 was created as a method to address the BPV-VIII-1-16-85 interpretation. I am intimately familiar with the issue (ok, I actually wrote the Code Case).

My reply on 4 Feb 18 20:01 was complete. Your specific situation is for a non-Code circumstance. However, if you were to follow the Code rules, what you are proposing (using allowable stresses not per VIII-1) would not be permitted, provided that the flange is in the scope of the vessel.

This concept of checking Design Pressure + Equivalent Pressure (from external forces and moments) for comparison to only the Rating Pressure is extremely conservative and should absolutely not be done. Code Case 2901 provides one method for doing this (but it is not the only way, BTW).

Checking existing flanges with Appendix 2 for managing external loads via equivalent pressure makes zero sense to me (although I recognize that it is done). You would be better to follow the rules in VIII-2 4.16.7 - at least that has provisions for external axial force and moments. That may satisfy U-2(g), provided that you maintain the use of VIII-1 allowable stress basis.

RE: Nozzle loads consideration for Flange rating selection.

Dear TGS4,
I am pleased to have this interaction with you.

With due respects to the discussions so far in this thread,my understanding of the subject is :

1. U-2 (g). Any design rules beyond this division to be as safe as provided by the rules of this division subject to the acceptance of the Inspector.

2. UG-11(c). Forged standard pressure parts to ASME product standard as listed in UG-44 are permitted in coded Vessels (to mean with or without code stamp). They shall be suitable for the design conditions of the completed vessel.

3. UG-22. Contains the loading to be considered as applicable, in the design conditions includes super imposed static reaction of piping which are understood as Nozzle loads.

4. UG-44 included standard rating flanges to ASME B16.5 & B16.47.

5. In these circumstances, standard rating nozzle flanges may have to be checked for Nozzle loads and in so doing, by taking CC 2901 and code interpretation BPV-VIII-1-16-85, the ratings are to be checked to fulfil Design pressure + Equivalent pressure due to nozzle load. This will be in compliance with U-2(g). It implies that if it fails in this, next higher rating to be adopted suitably. This looks quite conservative as remarked by you, but could be an assured safe practice.
5.1 This Nozzle load checking of standard flanges to coded vessels, are insisted by certain Engineering consultant, in view of not explicitly covered by code rules.
5.2 In case of Code stamped Vessel, if ASME-AI for code stamping, agrees for non checking of UG-44 standard flanges to Nozzle loads as above, there is no issue. But he should have a basis to do so.

6. Is there any Code program to provide more clear clarification on this subject.

I stand corrected for my understanding if any.

RE: Nozzle loads consideration for Flange rating selection.

Dear all,

Addition to all above information,Please see below:

ASME Section VIII Division 1 and ASME B16.5 do not include calculations to address standard flanges subject to loadings other than internal pressure and temperature. Therefore, in accordance with U-2(g), the Manufacturers subject to the acceptance of the Inspector, shall provide details of design.

The following, in no particular order, could be used as supporting calculations in my view. if incorrect then please guide me:

(a)Method in accordance with 4.16, in particular, 4.16.7 of ASME Section VIII Division 2
(b)Equivalent pressure (*) method in accordance with the following:
(i) NC-3658.1(b) of ASME Section III Subsection NC.
(ii) Evaluation of Flanged Connections Due to Piping Load by D. L. McKeehan & L.C Pang of M. W. Kellogg Co.
(iii) Note 10 of Design of Flanges Procedure 2-7 (page 54) of Pressure Vessel Design Manual, 2nd Edition, by Dennis Moss.

(*) Equivalent pressure method (i) converts the external bending moments into an equivalent pressure.The equivalent pressure can then be added to the internal design pressure and the total pressure can then be compared with the maximum working pressure specified in the applicable ASME Standard (e.g., ASME B16.5).


Other calculations methods acceptable to the AI may also be considered.
Another option is to consider whether or not the flange may be excluded from the geometric scope of the ASME Certification Mark stamp and the Manufacturer’s Data Report [ref. U-1(e)(1)(-a) and (-c) of Section VIII Division 1].

Kindly suggest if any further or additional methods available.

RE: Nozzle loads consideration for Flange rating selection.

Israr1, there is no requirement of calculation to ASME B 16.5. the check rating pressure to be only taken as Design pressure + Nozzle load equivalent pressure as being discussed.

If we limit our discussions to ASME Sec VIII div1, my steps of considerations may be straight ones.

All this arises when the client desires to check standard Nozzle flange rating considering design pressre + Nozzle load equivalent pressure. Other wise presently there is no explicit code requirement to do so.

RE: Nozzle loads consideration for Flange rating selection.

DWARAKAKRISHNA - your post of 7 Feb 18 10:11 is essentially correct. In your item 5, just ensure that the MAWP + Equivalent pressure is compared to the appropriate quantity - which is something more than just the rating pressure.

My comment was that comparing it to only the rating pressure was conservative. If you follow the equation in CC2901, and you pass, then you're ok. If not, then you need to change something. The magnitude of the nozzle loads would be my first thing to change. Then I would look at challenging the design pressure. Finally, I would look to increasing the flange rating class.

israr1 - see Code Case 2901. Do not compare the design pressure + equivalent pressure to only the rating pressure. That is excessively conservative.

I would add the Method by Bill Koves as published in the ASME Journal of Pressure Vessel Technology MAY 2007, Vol. 129.

RE: Nozzle loads consideration for Flange rating selection.

TGS4. Thank you so much for your authoritative views.
I enjoyed the professional level discussions on this subject by all respondents.
Is Bill Koves method reflected in CC and Code interpretation. Otherwise can I have it.
Any ASME program emerging to provide clear rules on these matters.

RE: Nozzle loads consideration for Flange rating selection.

Dr. Koves method is available in the JPVT. You can buy it from the ASME Digital Store or your local university library. It is not currently planned to be placed into the Code at this point, but if there is a request to do so, we will consider it.

Code Case 2901 is in the process of being incorporated (BC17-1071) into UG-44 in VIII-1 and 4.16 in VIII-2. It is still working its way through the committees, so it may or may not make the 2019 Edition. If it does make the 2019 Edition, then we will annul CC2901.

Anything that emerges will be as crystal clear as the Code itself.

RE: Nozzle loads consideration for Flange rating selection.

Quote (TGS4)

Anything that emerges will be as crystal clear as the Code itself.

Ah yes, Always, Sometimes, Maybe, Except :)



The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Nozzle loads consideration for Flange rating selection.

SnTMan - exactly.

RE: Nozzle loads consideration for Flange rating selection.

Can I have a liberty to extend the original discussion here?

Code case 2901 seems clearly restricting scope of applicability to WELD NECK Flanges, in title and Inquiry statement. Does that mean one can not use same method for evaluating reduced MAWP for Slip-on flanges? what is the intent for filtering only weld neck flanges out of UG-44(b), (i) & (j)i.e ASME B16.5, B16.47?

Thanks for enlightenment, in advance

RE: Nozzle loads consideration for Flange rating selection.

The research behind the Code Case was only performed for weld neck flanges, and not other styles. Until such time as research is done, this method will not be extended to other flange styles.

Does that answer your question?

RE: Nozzle loads consideration for Flange rating selection.

Thank you Mr. TGS4. Yes, that did answer my question sir. But then what is the best alternative to analyse standard B16.5 & B16.47 flanges 'other than weld neck flanges'? Same equivalent pressure method that is in practice; but without moment factor (considered in CC2901)? Right?

RE: Nozzle loads consideration for Flange rating selection.

I honestly don't know. There simply hasn't been research (either experimental or numerical) on this topic.

RE: Nozzle loads consideration for Flange rating selection.

Okay, thank you for the clarification.

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