Lap Joint dimensions >24in ?

[mrpsi]

Hello,
Are there any published Standards or "industry practices" that govern the size of laps (stub-ends) for large diameter (>24") lap joint flanges.

ASME B16.9 covers pipe sizes up to 24", but beyond that I can't find any guidance other than extrapolating the B16.9 sizes. I'm running Appendix-2 calcs for large (>24") diameter lap-joint flanges and the calculations are very sensitive to the stub-end (lap) OD.

Try as I may, I cannot find any guidance.

Thank you very much,
MDR

 

[SnTMan]

mrpsi, I can't say for certain, but I think you are in totally custom territory, and you will just have to make your own decisions and tradeoffs.

To some extent, the lap dimensions will be governed by the selected gasket dimensions, which you probably figured out already.

Good luck.

Regards,

Mike

 

[doct9960]

mrpsi,

What do you mean "sensitive" to the lap OD? Can you be more specific?

Are you going to use custom gaskets or standard gaskets that conforms to ASME B16.47 Series A or B? If standard gaskets, then use a lap OD than conforms to the facing diameter of an ASME B16.47 Series A or B flange. If custom, you can design to anything you want.

 

[mrpsi]

SnTMan & doct9960,

Thanks for your responses.
Regarding points that have been raised:

-Sensitivity: Per Appendix-2, Fig.2-4 (1), for Lap-Joint flanges at seating, the location of G, and thus the moment arms hG & hT, are taken to be at the midpoint between Lap OD and Flange bore (the contact between them). This is unique in that it is independent of gasket size and location. This is why a small change in the lap OD has a large effect on the seating requirements.

-Gaskets: The gasket that I am using is a spiral wound conforming to B16.20, for large diameter.

-Approach:
a) The most conservative approach is to assume that the lap joint OD is at the gasket outer edge. This results in the longest moment arms hG & hT, driving the flange thickness up. This has been suggested above.
b) The least conservative approach is to take the lap OD out so that it just clears the bolts, thus reducing the moments, and reducing the thickness requirements.
c) I would like to take a 'realistic' approach, hoping to find a company standard to use as a baseline or starting point. Perhaps I'll need to send out an official survey of piping installations.

 

[SnTMan]

mrpsi, as a practical matter I would not make the lap OD smaller than the gasket outer ring. If it requires a little thicker flange, so be it.

Out of curiosity, what difference in flange thickness are you getting between a) and b)?

Regards,

Mike