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  1. #1

    request: nozzle local stress analysis by Annex G of PD5500 in PvElite

    i am working on designing of a PD5500 - 2012 pressure vessel by PvElite 2014-sp2 software. after opening Nozzle input/Analysis menu, i select in calculation method bar, PD:5500 item. now my question is:
    if the nozzles on vessel doesn't have reinforcing pads (integrated type):
    i. should i consider membrane stress intensity factor alone for nozzle (1.2 f) or i must check only membrane+bending stresses (2.25 f) for nozzle local stress analysis by PD5500?
    should i check the Print membrane stress at nozzle Edge box for analysis of nozzle by Annex G of PD or not?
    please sea the attachment.

    more explain:
    A.3.3.2 paragraph in PD 5500 - 2012 says:
    A.3.3.2 Nozzles and openings subject to pressure and externally applied loads
    For these limits to apply the nozzle or opening has to be reinforced in
    accordance with 3.5.4.
    The maximum stress intensity adjacent to the nozzle or opening due to internal
    pressure shall be obtained from G.2.5 in the case of spherical shells, or from
    G.2.3.6 for cylindrical shells.
    Under the design combined load the stress intensity due to the sum of
    membrane and bending stresses shall not exceed 2.25f.

    our consultant based on above paragraph and example W.3.2.3 of pd 5500, interprets that there is no need for considering membrane stress intensity (1.2f) separately. so based on your answer, his interpretation is incorrect. i am right?

    thanks in advance for your help and PD 5500 - 2015 is a gift for the best answer.


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  3. #2

    Re: request: nozzle local stress analysis by Annex G of PD5500 in PvElite

    Dear Mohamad3010,

    [link Point to another website Only the registered members can access]
    Maximum Membrane Stress Intensity needs to be calculated at the nozzle OD. See the red cloud in the attached file. It says at the edge of re-pad or attachment or support. In the working example there are two forms used for calculation. One for nozzle OD and the other for re-pad OD. If you look at OD and thickness are different for both tables due to presence of re-pad. But in case of self reinforced nozzle 1.2f and 2.25f needs to be calculated at the OD of nozzle.

    Regards,
    aspa


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  5. #3

    Re: request: nozzle local stress analysis by Annex G of PD5500 in PvElite

    It is true that Annex W does not compute the membrane stress at the attachment edge. In the same time, I think it is clear enough that Annex G considers that the membrane stress contains intensified stresses due to the presence of the hole. However, by engineering background, one can remember that this may be necessary when the subject is fatigue, but may not be necessary where this condition does not obtain.

    This is confusing and contradictory and in my opinion Annex W is wrong just because does not follow the "spirit" of Annex G of PD 5500 and the missing calculation brings unsolved questions. But adopting the concept of stress concentration factor give you the opportunity to be on the safe part, isn't it? and this is one argument that cannot be ignored.

    I guess that's why in PV Elite Coade/ Intergraph put the option to check the membrane stress at edge as an attempt to solve this endless dilemma- must be checked? may be missing?
    To check it, you must activate Print the membrane stress. You are right- this is confusing, too (I mean it seems that my choice would be to print it rather than to compute it)- but is the approach of Coade/ Intergraph to put software options in a strange ways and places... at least this is my perception.

    Only a guess about your consultant.... For many years the primary method for computing the stress in nozzles that have a mechanical loading has been WRC-107. The stresses computed with this procedure were then compared with the ASME Code allowables. WRC-107 does not classify the stresses. General practice in many industries has been to compare only the Primary plus Secondary (P + Q) Stress Intensity due to the mechanical loading to 1.5Sm. While the membrane stresses are computed, they are not always compared separately with the 1.5Sm criterion. Maybe your consultant was so immersed in this approach that he/she tends today to extend it automatically to PD 5500!
    What I try to say is that an educated and old enough engineer may be reluctant to enthusiastically adopt the concept of Stress concentration factor at the attachment edge just because for many years limiting only (P + Q) Stress Intensity as per ASME was satisfactory when worked with WRC, while checking the local stress may be missing.
    And a final question... Why one would think that considering a PD5500 concept that is close to fatigue subject shall address a real issue, whereas the same PD 5500/W does not calculate it for a regular case?
    But it may be something more than I tried to guess. Your consultant may have a deep knowledge on some articles and/ or may have experience on FEA works.
    Recalling ASME now (because the reader would be more familiar with), it is clear that well away from the nozzle the General Primary Membrane stresses in both the shell and nozzle are to be below Sm. In fact, as a measure of how close to the nozzle we can be before the membrane stress is allowed to exceed Sm, we can take guidance from ASME Section VIII, Division 2 Appendix 4, where there is the definition for Local Primary Stress. So beyond the limits of Local Primary stress, the General Membrane should be kept below Sm and this is a valid rule. But for Local stress, it is the exception rather than the rule when a conventionally designed nozzle will meet the local membrane criterion (1.5Sm) at the junction-ring if the bending loads are included and for this reason so many engineers are happy accepting the status-qvo. Simply said, this criterion is told to be inappropriate and must be replaced with something more realistic. Or we may accept it keeping in mind is conservative.... The same may be said about PD5500 and the reference to ASME I've done is for similitude only.

    In the end I will mention a paper which has the title A Proposed Method for Finding Stress and Allowable Pressure in Cylinders with Radial Nozzles. It does not bring light to your query but it is interesting to know it for "historical" reasons. PVP-399 is a ASME Pressure Vessel and Piping conference publication and is from the 2000 presentation. Therein was Mr. Bildy’s first presentation of an alternate analysis method for nozzle openings. This paper was later adopted as a Code Case for the ASME Boiler & Pressure Vessel Code (Code Case 2398). And Code Case 2398 was later adopted into ASME Boiler & Pressure Vessel Code Section VIII Division 1 as Appendix 1-10. Moreover, Code Case 2398 was later adopted into the ASME Boiler & Pressure Vessel Code Division 2 "rewrite" of the 2007 Edition. It is available at

    [link Point to another website Only the registered members can access]
    A valuable guidance more linked to your case may be found on

    [link Point to another website Only the registered members can access]
    My best regards.
    Marian

    PS I am not fighting for a gift, it is just an attempt to answer giving my understanding on your query. I'm sure that, when you'll conclude that is worth to upload PD 5500 - 2015 you will proceed in this way, giving the gift to everybody.

    Thanks to you and many others (I just hope that I do not offense them not mentioning their names!) we have access through a prohibitive turnpike of engineering, where "the Corpogods" ask for incredible high amount to access by. True, they must sustain their activity but when put such pressure of pecuniary difficulties on engineering shoulder must recall in mind the Laffer curve (or in words "increasing taxes does not increase revenue"). True again, this sentence is not to legitimate infringing copyright and it is not a moral matter to be solved in this forum.
    Actually, what I want to say is just "Thank you again" because what you folks uploaded here help me improving my engineering knowledge.

    Last edited by marian_g; 10-04-2015 at 04:49 PM. Reason: added more explanations

  6. #4

    Re: request: nozzle local stress analysis by Annex G of PD5500 in PvElite

    It was a rather long post and maybe it was not so clear.
    I have only a question: how your consultant considers the requirements of PD5500/ A.3.4.2.2 are fulfilled?
    Or his strategy is to adopt only A.3.3 (Specific criteria for limited application) and to ignore A.3.4 (Specific Criteria for General application)?
    Last edited by marian_g; 10-07-2015 at 04:10 PM.

  7. Re: request: nozzle local stress analysis by Annex G of PD5500 in PvElite

    Mohamad,

    From which paragraph of PD5500 is coming up the requirement " membrane stress intensity factor alone for nozzle (1.2 f)"?

    My threads; mariog :


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    • #6

      Re: request: nozzle local stress analysis by Annex G of PD5500 in PvElite

      my friend, this is exactly my question : shall we calculate only the sum of membrane and bending stresses (2.25f) or we also shall calculate membrane stress intensity factor (1.2 f) ?
      in my case, the sum of membrane and bending stresses are limited but membrane stress intensity exceeds the limit. consultant says that no need to check the membrane stress intensity. i ask he is right or not.
      maybe i should check it by FEA analysis.
      thanks.

    • #7

      Re: request: nozzle local stress analysis by Annex G of PD5500 in PvElite

      Mohamad3010,

      Are you talking about allowable stresses?

      As far as local load analysis calculation is considered, we always need to do calculations for

      - Pure membrane stress (Allowables: S)
      - Pure membrane + local membrane stress at discontinuity and due local loading like nozzles (Generally Allowables: 1.2S to 1.5S)
      - Membrane + Bending stresses (Generally Allowables: 2.25S to 3S)

      Regarding whether you should check the box for "Print membrane stress at nozzle Edge" will not affect your results. It will just print the calculated results in report.

      Thanks.

    • Re: request: nozzle local stress analysis by Annex G of PD5500 in PvElite

      Dear All,

      The original question of Mohamad was
      "should i consider membrane stress intensity factor alone for nozzle (1.2 f) or i must check only membrane+bending stresses (2.25 f) for nozzle local stress analysis by PD5500?"
      His question is based on PD5500 2012 edn, paragraphs A.3.3.2 and G.2.3.6 for cylindrical shells, where checking against 1.2 f seems to be not required.

      My understanding of the requirements of PD5500 is as followings:

      - in A.3.3.1, the membrane stress intensity is limited to 1.2f; however this paragraph refers to "attachments and supports", whereas the "nozzles and openings subject to pressure and externally applied loads" are subject to requirements of A.3.3.2 which not include reference to "1.2f". Why borrow this limit as applicable for nozzles?

      -in A.3.3.2, the requirements refers to the calculation of the maximum [local] stress intensity, according to G2.3.6 and ask to check the sum of [local] membrane and bending stress" against 2.25f; I added [local] because this is included into the title of G.2.3.6.
      In G2.3.6, a combination of [local] stress due to pressure with [local] stress due to local loads. For nozzle OD, the local stress due to pressure, namely fp, has formula (G.2.3-3) by which a stress concentration factor is already included as 2.25(Ceas/eps)/1.1 (uncommon to ASME philosophy, I would add). In my opinion, proceeding as in the "suggested form G3" you don't need to recheck the stress as they are defined in A.3.4.2.2 or A.3.4.2.3.

      I would conclude that your consultant is correct.
      I don't know what PV Elite suggest there because I don't how PV ELite took the input data and calculated the "membrane stress at attachment edge"... moreover, we are not talking about "attachment" but on "nozzle" which is clearly different in PD5500 terminology.

      My threads; mariog :


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