Flange calculation 6

[farzam]

Dear All,

I have a vessel (12")with body flanges I selected the flange acc. ASME B16.5(Temp-Pres.)but our client asked me to perform flange calculation acc. ASME VIII-App.2!! I specified standard flanges acc.B16.5 so i do not see any requirement to follow App.2
please let me know your opinion

Thanks in Advance

 

[prex]

If your code is ASME VIII Div.1, you are correct, you don't need to calculate the flanges for pressure only (and be careful, you could have a bad surprise, not necessarily B16.5 flanges meet App.2 criteria).
I would ask the client to motivate their request: it might be justified by some special conditions (e.g. external loads, but of course you should be aware of them).

prex

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[FabianoRibeiro]

Take a look at UG-11(a)(2) and UG-44. There you can confirm what prex is saying.

Regards.

 

[TomBarsh]

The fact that these are body flanges indicates that the flanges may be subjected to loads from weight, wind, seismic, etc. In this case additional axial force and bending moment may be acting on the flange.

For such conditions it is often done that an equivalent pressure is deteremined from the axial force and bending moment. This procedure is described in ASME Section III (I forget the paragraph) and in a number of vessel design handbooks. For example, see the book by Dennis Moss, Appendix G. The equivalent pressure is added to the design pressure and static head to determine the required flange rating.

 

[rumandcola]

Have the flanges been modified so that they no longer meet the geometry specified in B16.5? If not, then there is no reason to provide Appendix 2 calculations. As Prex mentioned B16.5 flanges will often fail an Appendix 2 calculation.
If they are looking for calcs for external loads, wind, seismic, etc this is not covered in Appendix 2.

 

[ctcs117]

B16.5 is for pipe flange.
if your body flange is Girth flange, you have to calculate as App.2 based on load and gasket characters(dimension/y/m).

 

[vesselfab]

HUH?

Here's the short version,
If your 12" body flanges do not have to resist any external loadings such as wind/seismic/piping loads you can simply use b16.5 ratings. like it is high in vessel with no pipe outlet or used as a top access.

If it is lower in the vessel and has pipe loads in nozzles above it, or there is wind or seismic loads you should use appendix 2.

you often have to use a rating above the standard b16.5 and a thicker hub. But it is still easier than a custom machined flange

 

[TGS4]

ctcs117 and vesselfab, I will have to disagree with you. B16.5 flanges are acceptable for being body flanges anywhere in a vessel (point me to the paragraph in B16.5 that says otherwise). So long as the pressure-temperature rating is maintained you will be fine.

Regarding going to the App. 2 calc, nowhere does that calc include for external bending moments of axial forces. So, using that calc wouldn't be of use - as as mentioned by prex, above, may show that you have a problem, when you really don't.

If your issue is worrying about leakage of the body flange under external bending moments, crank-up the bolt pre-stress (start@ 50ksi assembly bolt stress, and keep increasing it until you have no leakage). Stay below the bolt yield stress, by a reasonable margin - at least 10-15% due to scatter in the bolt stress caused by the assembly technique.

Don't worry about the strength of the flange - this paper

http://asmedl.aip.org/vsearch/servl...s=ASMECP&key=DISPLAY&docID=4&page=1&chapter=0

shows that you don't have to worry about it.

 

[gr2vessels]

My two cents;-
The girth flanges per B16.5 can see any of the mentioned external loads, converted into equivalent pressure. Add this to the design pressure and make sure they do not exceed the flange rating (pressure / temperature).
It's really not that complicated.
Cheers,
gr2vessels

 

[doct9960]

Here are some papers on equivalent pressure for your enlightenment (or confusion)...

http://www.pipestress.com/papers/Eval-FlageConn.pdf

http://www.coade.com/ubb/Attachments/368-3_EQPRESSURE.pdf

http://www.coade.com/ubb/Attachment...he_equivalent_pressure_for_piping_flanges.pdf

 

[LSThill]

doct9960 (Mechanical)

Not cover last week in the course by Kan in Houston Div 2

Thank you
Steve Thill

 

[C2it]

You don't need to do equivalent pressure if you design your flanges to ASME VIII Div 2 (2007 Ed.)Section 4.16. This allows direct inclusion of external loads in the stress calculation.

 

[gr2vessels]

I still believe that you don't need to do any ASME VIII verification for the B16.5 flanges, provided the equivalent pressure is included in the design pressure of the vessel. Regardless of the flange fitted to a nozzle or it is a girth flange.
Cheers,
gr2vessels

 

[vesselguy]

All custom made flages on vessels are designed per Appendix2. Since this is an off the shelf B16.5 flange, of course you DO NOT check this against Appendix 2. If you do, it is likely the stresses won't meet the allowables.

Let's just step back and look at this case from common sense. This is a 12" dia vessel using a 12" flange; it does not matter if it is used as a body flange or a nozzle flange. It might as well be a 12" pipe. Does everyone do a bunch of Appendix 2 calculations on all piping flanges? No. The argument of wind loading on the body flange don't add up either unless this body flange used to join another tall segment of vessel shell. This is stretching a bit of assumption are we not?

If a client insist on forcing you to do an Appendix 2 calculation then do it. No argument needed. Just give him the cost adder for machining a set of flanges to meet Appenix 2 when the ASME flange don't meet Appendix 2 criteria.

 

[gr2vessels]

Correct assumptions above;- the body flange can be bolted together with a B16.5 blank flage. In that case obviously no external loads should normally be included (unless a lifting lug is welded on the cover!). It is also obvious that a 12" dia column (say 7' tall) which is flange bolted on top of a horizontal vessel, is affected by external loads like wind and seismic loads, perhaps some significant piping loads too. These loads will affect the rating of the joining flanges by the amount of external loads converted to equivalent pressure (refer also to Appx 2, Clause 2.1(a), last sentence: "Proper allowance shall be made if connections are subject to external loads other than external pressure").
Cheers,
gr2vessels

 

[160970]

It is better if you can use sofware like caesar/autopipe or pvelite for flange analysis.

 

[TGS4]

160970 - Care to provide a justification for your statement?

 

[MalcolmA]

As stated in the above posts, B16.5 flanges won't always pass an appendix 2 calculation. Does anyone know what calculations have been done to design B16.5 flanges?

 

[gr2vessels]

MalcolmA,
Free download from internet 'Modern Flange Design Bulletin 502" by Taylor Forge (J. Hall Taylor).
Cheers,
gr2vessels