External loads on flanges and UG-44(b) 1

[ElCidCampeador]

Hi,

I have a nozzle (seamless pipe+standard WN acc. to B16.5) designed acc. to ASME VIII Div.1 with external loads acting at shell/nozzle intersection and checked acc. to WRC.

Question: Does UG-44(b) apply?

I mean, loads are acting not directly at flange joint, so may I assume "External loads (forces and bending moments)" of UG-44(b) equal to zero and skip UG-44 calculations?

If not, I suppose I have to verify flange according to appendix 2 (bolts are B7M material so they don't have an allowable stress greater than B8 Cl.2, as (b)(3) requires).


Thanks

 

[BJI]

The external loads have to be considered, yes. It is a big assumption given the proximity of the nozzle junction to the flanged joint, so no. If you have calculated the loads at the joint, and there is a point of contraflexure or notable reduction at the bolted joint, then I don't see why you couldn't define separate loading, however, this would have to be clearly documented. I don't believe it was the intent of the original method to exclude B7M bolting, based on the ASME adaptation, this limitation would only apply to bolting less than or equal to 3/4". I believe the intent was to require high strength bolting, that could be assembled to reasonable bolt loads, which would include B7M bolting.

Does UG-44(b) have to be used, no, other methods may be used. ASME III NC-3658.3 defines high strength bolting as having an allowable strength not less than 20 ksi, which includes B7M bolting.

Appendix 2 calculations for standard flanges would not be appropriate IMO.

 

[StressGuy]

"loads are acting not directly at flange joint"

How are the loads getting to the shell/nozzle junction, if they're not going through the flange?

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[ElCidCampeador]

I agree with all of you.

But UG-44(b)seems to refer only to "welding neck flanges". And what about long welding neck (straight hub)?

 

[BJI]

It depends on who is reviewing, the current wording is for weld neck flanges since this is what was used in the original research.

Material is added so the LWN neck flanges are stronger than WN flanges. There is less flexibility however, so there is a chance you could get an increase in radial stress at the hub ring junction (not a major concern). Overall, I couldn't see how you would get a reduction in flange limit sufficient to alter the published moment factors.

The assembly bolt loads are required to comply with ASME PCC-1, and I wouldn't see any issue with applying the same bolt loads calculated for WN to a LWN flange. The moment factors for WN flanges are calculated assuming PCC-1 assembly bolt loads.