How to verify the reinforcement and rigidity of large blind flange with nozzle

[jt1234]

Dear all,
I have a low alloy 30"-600# ASME B16.47 manway blind with 8" nozzle welded to the blind. Note that the nozzle will have axial force and bending moment acting on the blind too. What is the method to include MAWP and external piping load to calculate the nozzle hub reinforcement to make sure blind opening is sufficiently reinforced and the rigidity is good so no leak will occur ?
Vessel supplier using Div 1 Appendix 2 to verify the design and came up with twice of the flange thickness, which I think is overkilled and will cost a lot.

 

[SnTMan]

jt1234, tough problem, no neat rules-based way to solve it. For purposes of discussion I am going to refer to Sec VIII, Div. 1, as existed under 2017 Edition. If some magic exists in newer Editions, I am unaware.

1) Nozzle reinforcement: Blind required thickness can be calculated per UG-34. nozzle reinforcing per UG-39. So far so good.

2) No good way to account for external loads in the above. I don't recall that methods such as WRC-107 apply to flat plates. About the best you could do is treat these as an additive, equivalent pressure per the Kellogg or similar method. Additive to vessel MAWP if you wish I suppose. Not so good but do-able.

3) Flange rigidity does not, strictly speaking apply, apply to blinds. One approach would be to treat the blind (with opening) as a loose flange (possibly with hub) under Appendix 2, and perform those rigidity calculations. Whether this calculation would jive with calculations under 1) above is anybody's guess. Probably worst yet.

This just might be a case where FEA is warranted

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[jt1234]

Hi SntMan,
Thanks for the reply. I am not in favor of using FEA to justify flange. Flange is different from plate which allows for deformation such that code does not have deformation limit. Rigidity is the key for flange however there is no allowable deformation for flange that even it passes stress analysis, the deformation may lead to leak.

But you got a good point # 3 using Appendix 2 to check the rigidity. My plan is to make sure it is reinforced as your point # 1, and check rigidity using original flange thickness, and most likely ignore the overstress report.

 

[Trestala]

Calculate it like a reducing flange, 8"x30". Add a hub section to the opening similar to a WN flange.

The flange OD, bolt circle dia./size/qty, and flange thk., would be the same as a 30" 600# B16.47 flange.
But the flange I.D. is for an 8" pipe. Design a hub section with thickness and length similar to a standard 8" flange as initial dimensions.
You can consider the nozzle loading as an equivalent pressure.

Is that what your supplier did?

 

[LittleInch]

That sounds about right to me.

ASME VIII div 1 App 2 is pretty notorious for "failing" standard ASME B 16.5 or 16.47 flanges even with no additional loads.

Cut a large hole in it, add some mysterious "nozzle" - Is it even a weldolet shape? - plus some unspecified axial and bending loads and I'm surprised you got away with double.

Alternative is do it in piping? So 30" to 20" to 12" to 8" reducers welded together gets you the same thing using standard components to B 16.9.

got a drawing or sketch of this thing?

Some level of hub reinforcement may make it better, but depends on the level of these additional loads you're putting on this flange.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jt1234]

Thanks all of your replies above. Yes vendor was doing what you described, very typical design, nothing special. 8" is process nozzle. there is no room for additional reducers and it is not economical to add so many reducers.
One day, Code shall address this issue, as it is so common in any petrochemical/ refinery plants.

 

[r6155]

The required nozzle thickness of 30" is with UG-45 but is not considered an inspection opening.

Regards

 

[EngineerEPC]

Hi,

FEA seems to be the only option, I had encountered the same concern, and we have performed FEA of blind flange with nozzle, as AI was insistent for resolution of external load into blind flanges.

Thanks and regards

 

[r6155]

IMHO this is not a good design, inspection and testing is complicated during construction and service.
I prefer a separate connection.

Regards