ASME B16.5
ASME B16.5
(OP)
Good day Everyone
I have a question referring to flanges acc. to ASME B 16.5. According to point UG-44 of ASME VII Div.1, if flanges, gaskets and bolts fulfilled requirements of listed there standards, is enough to choose flanges only based on calculated pressure-temperature rating in referring to design parameters and assumed flange material. And in may particular case for flange 2 inch class 150, for design parameters 0.82 MPa and 343 oC, calculated rating 150 is good enough. But if I make detail strength calculations of this flange with spiral wounded gasket with dimensions acc. to ASME B 16.20 with coefficients m and y taken from Table 2-5-1 of Annex 2, I reach overload in Radial Stress. Same situation I have for blind flange for above described flange, offcourse there is a problem that nominal thickness for 2 inch blind flange is not enough. For flanges chosen material is SA-350 gr.FL2 Cl.1 and corrosion allowance is 6 mm. Such problem, I have also for example for LWN nozzles 20 and 24 inch class 150. There are overloaded stress in hub. Therefore, I would like to ask you whether I could accept such flanges chosen based only on rating thought that strength calculations gives unsatisfactory results. And how I shall do in future.
Thanks for advice.
I have a question referring to flanges acc. to ASME B 16.5. According to point UG-44 of ASME VII Div.1, if flanges, gaskets and bolts fulfilled requirements of listed there standards, is enough to choose flanges only based on calculated pressure-temperature rating in referring to design parameters and assumed flange material. And in may particular case for flange 2 inch class 150, for design parameters 0.82 MPa and 343 oC, calculated rating 150 is good enough. But if I make detail strength calculations of this flange with spiral wounded gasket with dimensions acc. to ASME B 16.20 with coefficients m and y taken from Table 2-5-1 of Annex 2, I reach overload in Radial Stress. Same situation I have for blind flange for above described flange, offcourse there is a problem that nominal thickness for 2 inch blind flange is not enough. For flanges chosen material is SA-350 gr.FL2 Cl.1 and corrosion allowance is 6 mm. Such problem, I have also for example for LWN nozzles 20 and 24 inch class 150. There are overloaded stress in hub. Therefore, I would like to ask you whether I could accept such flanges chosen based only on rating thought that strength calculations gives unsatisfactory results. And how I shall do in future.
Thanks for advice.





RE: ASME B16.5
It is true that many standard flanges will not meet their B16.5 pressure-temperature rating when analyzed by ASME Section VIII Div 1, App 2. ie: The flange MAWP found per App 2 may be lower than the published rating.
On the other hand, many "stockier" standard flanges will have an MAWP per App 2 that is greater than their B16.5 rating.
I am surprised that the 2" Class 150 wasn't one of these that falls into the "stockier" category (a 24" Class 150 would certainly be the "non-stocky" type with lower MAWP).
RE: ASME B16.5
I fully agree with TomBarsh that it is well-known in industry that many B16.5 flanges fail the Appendix 2 calculation. From a strength perspective, I would recommend Div. 2, Appendix 4 analysis. From a leakage perspective (and aren't all flanges designed so that they won't leak???), you're going to have to look farther afield than the ASME Code.
My recommendation - EN-1591-1.
RE: ASME B16.5
From my designer experience, I have always checked even standard flanges. And if the result of analysis has been unacceptable I have choose flange from upper rating class. But now my client request only design base on rating calculation, therefore I have some objections to this. But now I can accept such solution, especially that I have made strength analysis with using of calculation software, which include in strength calculation corrosion allowance automatically, what gives in result thicker wall.
RE: ASME B16.5
RE: ASME B16.5
I hear no end of questions about how to specify corrosion for standard flanges.
And now that ASME Section has finally adopted the 2003 Edition of B16.5 (per Table U-3) we can toss out that decade-old copy (well, better keep it around).
Another point: The pressure-temperature ratings may (and do) vary with the Edition. Some materials in the new Edition have little changes in their pressure rating at given temperature, like + or - 5 psi here and there. So flanges that passed in older Editions may no longer pass with new Edition.