Maximum Allowable working Pressure for girth flange

[roniprabowo]

Dear all,
Does anyone know how to calculate the MAWP for girth flange type 3a in appendix 2 in ASME Sec VIII ?

Looking forward for your information.

 

[mullodon1]

You'll have to use Code B16.5. Go to Table 1A to find the
Material Group the flange is made from. Use that material Group to find the rating in Tables 2. The pressure at the particular temp will give you the MAWP.

 

[TomBarsh]

Flanges designed to ASME Sect VIII Div 1 Appendix 2 and those manufactured per ASME B16.5 are accepted based on different criteria. There is no assurance that a B16.5 flange will meet its standard pressure-temperature rating when analyzed per Appendix 2.

To determine the MAWP of a flange designed per Appendix 2 requires the simultaneous solution of multiple equations: those equations for calculated stress defined in Appendix 2.

Practically speaking, it is simpler to have an electronic spreadsheet, MathCAD worksheet, or computer program, etc, each written to calculate the stresses as per Appendix 2. Then manually (or let the computer software do so automatically) iterate to find the pressure that corresponds to one of the calculated stress becoming equal to the allowable stress: by definition the pressure that corresponds to the first calculated stress (Sh, St, Sr, or one of the defined combinations) just meeting its corresponding allowable stress is the MAWP; any higher pressure will result in the allowable stress being exceeded.

Because of the wide variations in geometry, gasket properties, etc there can be few, if any, generalizations made about what may in general be the limiting factor when determining the flange MAWP. Thus there aren't any shortcuts to the process described above.

One generalization that can be made is that many B16.5/B16.42 flanges do not meet their published ratings when analyzed per Appendix 2. On the other hand, a number of these flanges actually exceed their published ratings. In practice it seems that the very small diameter (and proportionately "heavier" than their larger diameter “classmates”) flanges will exceed their rating, while the larger diameter flanges will not meet their ratings.

 

[prex]

In the site below, under Vessels -> ASME VIII Div.1 -> Appendix 2 -> 2.7:loose , there's a calculation form for a fig.(3a) flange: if you set the dimensions according to yours (they'll appear in blue) and leave the working pressure in green (calculated by program), you'll get the MAWP of your flange.

prex

http://www.xcalcs.com

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