Do you check Stress ST when design a blind flange? 2

[Spoonful]

Dear All,

When you do a design for blind flange use UG-34 (c) (2), formula (2) it refer to Appendix 2 for W & hG

In appendix 2, it calculate 3 stresses for SR SH ST, for a blind flange, being lose type flange with no hub, then SR SH are ZERO. How about ST, do you need to check for ST for blind flanges? or it is only required for ring type flange? but isn't blind flange also a ring type flange?

When check the calculation with PVElite/CodeCalc, it dose actually calculate ST.

My understanding of ST is it caused by the internal pressure acting on the flange ID and also moment caused by hydro force and bolting. for blind flange, they will not be a internal pressure acting on ID, but still a component of the stress caused by the bending moment. Any comments?

Thanks

 

[prex]

A blind is not a ring type flange, it is a flat head. A ring reacts to the moment due to the offset between the hydrostatic load and the bolt circle by the so called 'false torsion effect', that's in fact bending about a neutral axis parallel to flange face. A flat head or cover, by contrast, reacts simply as a flat plate.
You only need to refer to App.2 for determining W, everything else, h[sub]G[/sub] included, is handled by UG-34. I can't see how S[sub]T[/sub] could be calculated for a blind, as Y is a function of A/B, B being undefined.

prex
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[Spoonful]

Thanks Prex, I agree with you a blind flange will act like a plate.

I am just a bit confused on understanding ST SR SH for flanges, do you mind give a brief explain of these?

 

[prex]

S[sub]T[/sub] is the classical bending stress in the ring section about a neutral axis parallel to flange face. S[sub]R[/sub] and S[sub]H[/sub] relate to the presence of the hub. All three stresses have complex formulae, as these account for ring's curvature and for hub's contribution.
In the simple case of a rectangular loose flange, S[sub]T[/sub] should equal, IMO, 6M[sub]O[/sub]/[pi(A-B)t[sup]2[/sup]] but YM[sub]O[/sub]/t[sup]2[/sup]B should be close to 2M[sub]O[/sub]/[3(A-B)t[sup]2[/sup]] so it's not really the same...??

prex
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