Flange Check

Dear All,

I want to do a flange check for subsea riser, I have modelled the riser piping according to ASME 31.8 , Now i want to know that, if i select the flange check option then which code will use to calculate the moment and forces in flanges.

my senior was telling that CAESAR II will not account the wave and current effect in flange check. Please give a clarification for this if anyone know.

Regrds,
rej...

You could do some test runs with a simple geometry and prove it for yourself.

The determination of forces and moments is based on the nodal displacements, which are based on the loads you define in a particular load case. This is all independent of any Piping Code.

Once the forces and moments are available, the specified Piping Code equations are applied to compute the stress values.

The flange check is independent of any Piping Code. This check uses the forces and moments from the indicated load case. If you have wave loading in the load case, this loading affects the forces and moments, which will affect the flange check.

Thank You Richard..

Dear Richard,

I have one more doubt about Caesar Flange Check.I believe that the allowable pressure given in the caesar output is taken from ASME B 16.5 .is it correct or not?

I am getting an allowable value of 255.4 bar for operation and 293.76 bar for hydrotest in the CAESAR output, whereas in ASME B16.5 Table 2.1.1 allowable value for 1500# flange at 33 degC is given as 255.3.why this allowable value for hydrotest condition is so high in CAESAR output ? I think it has to be same value.

Please help me to clear this confusion.
Regards,
rej...

Yes the allowable is from B16.5. The allowable decreases with increasing temperature, so what you state above makes sense. You can see the data used by viewing the file: "\ProgramData\Intergraph CAS\CAESAR II\6.10\System\ASME-2003.flg". This is a text file, so you can use NotePad to view the data. (The first column is temperature, then moving to the right you have the allowables for the various material classes.

thank you for your quickest reply.

But my doubt is that asme B 16.5 is giving maximum allowable pressure is 255.3 bar for a temperature range of -29deg to 38 deg, then how the allowable value is increasing for the hydrotest to 293 bar if the hydrotest is conducting at 20 deg.

Regards,
rej...

Dear Richard,

But my doubt is that asme B 16.5 is giving a maximum allowable pressure value of 255.3 bar for a temperature range of -29deg to 38 deg, then how can be the allowable value is increasing for the hydrotest to 293 bar if the hydrotest is conducting at 20 deg.

Regards,
rej...

CAESAR II increases the allowed pressure by the occasional load factor (k) for those load cases labeled (HYD) & (OCC). Your 293 bar is 15% greater than the B16.5 value of 255.3 bar. I would guess, then, that you are applying B31.1 or similar Code where the default k is 1.15.

Hi Dave,

Sorry for the late reply..
I believe that i am using 16.5 and i haven't changed any value of K in set-up file. If it is changed, then please tell me that how i can change back to the value 1.

Regards,
rej...

The Occasional Load Factor (k) can be set for your Occasional load cases in the Load Case Options tab in Static Analysis, right next to Flange Analysis Temperature.

Dave,

I got your point,but i am doing only the operational case so there is no occational load factor.i theink it could be better if you have a look on my caesar model .

am attaching the file with this reply.

Regards,
rej...

Your first load case is defined as "Hydrostatic". CAESAR II factors the allowed pressure by 1.15 for this case as well.

If you define a hydro load case then for the flange check software is multiplying by the occasional load case factor for that particular piping code. So, for B31.4 Ch IX it is 1.15, for B31.3 it is 1.33.

ASME B16.5 indicates that the system hydro test pressure can be up to 1.5 * rated pressure.

So, we can use 1.5 multiplier for hydro case for the flange check irrespective of the piping code if you are using ASME B16.5.

What if you define a flange check in your occasional load case. I could not find anything it said about the occasional load cases in ASME B16.5. I think for these cases there should not be any multiplier on the rated pressure.

Can user community provide feedback on these 2 proposed changes to CAESAR II software.

It should be a multiplier (not allways bigger than 1) for the rated pressure for all loadcases not necessary for occasional loadcases but based on some checks with other criteria (e.g. ASME VIII). Many times process engineers gives you the ASME B16.5 rated pressure as design pressure leaving no margin for external loads.

Regards,

Dan,

But, you use operating pressure and not design pressure in CAESAR II. So, the case that you said probably would not apply.

You are suggesting to add a new column in the load case option tab for flange check multiplier. That dialog already has so many options there...

If we cannot do that, then what do you think about the proposal as compared what CAESAR II is doing currently?

I think for gasket is no difference in "occasional" and "operating"; that's why you could not find anything about the occasional load cases in ASME B16.5

In this story, everybody tries to "conservative"; process engineer considers ASME B16.5 rated pressure as design pressure, stress engineer considers the rated pressure as leakage pressure and so on. As Dan said, in our days the piping system design pressure tends to be equal to the rating pressure of the flange then the system has exactly zero margin for external loads...

I think is rather an endless discussion and the evidence is flange survives at least to 1.5*p_rating, so I would be very comfortable (for initial design purposes) using a value of 1.5 times rating pressure when using the equivalent pressure method.

Personally I have no hesitation to consider Blick theory as giving realistic results provided that a sufficiently high assembly bolt stress/load was employed (and here I would correlate "sufficiently" with the assembly load applied in field-as ASME VIII details).

Anyway, Blick theory can be converted to a limit of "total pressure", see http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Number=34557
In 2010 I sent Blick's article to Coade/Intergraph.

I will also note an ASME/PVP2006 paper where the authors performed several FEAs on flanges that showed that they had substantially higher capacity versus the stress than what could be assumed per the rating.

It is a long discusion. In fact in the major part of the stress calculations only the design pressure is used (I will not comment for now if is a right or wrong approach, there are some reasons for this). Fact is that there is a column in the line list that nobody want to touch or discuss, and this is the design pressure. Clients want to see these numbers from line list in the calculations. Please remember also that many time the client do not have pipe stress skils, that will lead to a great loss of time and resources to convince him your calculation is ok.
Regarding the second point, I do not think that a global multiplier is a good idea as some flanges (I'm talking about size) can withstand more (in percentage) and some flanges less extra loads. My idea is to edit the text file (big work).
My personal opinion is that when we talk about flanges, it is not realy about the source of the loads, but about the magnitude.

Best regards,

One of the major O&G players use something like this in their specification.