Self-energizing O rings 3

[nachocivicos]

Hi,

In case of Self-energizing O-rings, strante behaviour appears when comparing integral and loose type flanges (ASME VIII, Div.1, Mandatory App. 2), calculated thickness for loose-type (sketch 4a) appear to be lower than for integral-type (sketch 7). How is it possible? I believed thickness for integral-type would always be lower than those for loose-type, when maintaining all other dimensions and materials. Any help?

Regards,
J.I.G.C.
Chemical Engineer

 

[nickelkid]

Check your calculations with paragraph 2-7 (formulas for calculating intergral and loose flange stresses). The Radial flange stress of the intergal type will lower it's Tangential stress versus the loose type.

 

[SnTMan]

nachocivicos, I would also add to be sure you are treating the various dimensions properly, see the relevant figures in APX 2.

Regards,

Mike

 

[nachocivicos]

Thank you very much for your help!

After reviewing calculations, I am not sure of which "h" value to use regarding sketch (7); I have noticed final thickness strongly depends on this parameter, which was previously advised to me to be taken as equal to weld leg. But after this advice I am afraid the same question remains,re-formulated: which "h" value should apply? The problem mentioned arose when using the "minimum 6 mm" value stated in the specific note on sketch (7).

Best regards, and thank you again,
J.I.G.C.
Chemical Engineer

 

[SnTMan]

nachocivicos, for this slip-on, integral type flange "h" (the weld leg) is the larger of 1/4 of the cylinder thickness (go) or 1/4" (6 mm). g1 is the combined thickness of the cylinder and weld leg.

This is easily determined from the sketch.

Regards,

Mike

 

[nickelkid]

If the nozzle wall(go) is 24mm or less h is 6 mm minimum.

Say the nozzle wall is 32 mm an 8mm minimum h is required.

 

[PVinspector]

nachocivicos,
Also, keep in mind unless you are machining a step or relief in the flange face so there is no metal-to-metal contact outside the bolt circle, you are not allowed to use Appendix 2 (see 2-1(a) Scope. O-ring flanges usually belong in Appendix Y and this is often misapplied.

You would have to calculate per Appendix Y, which is not a bad thing. If you do have a machined relief, you are OK with Appendix 2.