I have designed 1 equipment per ASME Sec. VIII, Div-1 having body flange at bottom (Bottom Flange-76") which is to be mounted on one tall vertical vessel at height approximately 127.5 m. The same part of that vertical vessel. The whole vertical vessel is derrick supported just below to the bottom flange of said designed equipment.

Now client has given external loadings (Axial force and bending moment) after 3 months of completion of design. Client wants us to use same loadings in body flange design.

Surprisingly, after communication with clients, it was informed that given loadings are generated in PV Elite based on wind loads at 127.5 m height where the bottom flange is attached.

Now my simple questions are:
a) Can we utilize wind moment generated due to wind load in body flange design
as external bending moment even though same is occasional loadings? Is it the way to
design a flange?
b) Isn’t piping or other mechanical loadings are only loadings that should be applied to flanges if given as external loadings?
c) Is there any reference which can help to deny such kind of loadings for body flange design?
d) If answer to question a) is Yes, then should we increase allowable by 20% as we are accounting wind loadings with pressure loadings?

My opinion is that this type of loadings generated due to wind (Occasional load) shall not be applied to flange design as external loadings. Only piping or other mechanical loadings shall be applied to flange design as external loadings.

Opinions or Views from Mr. Mandeep / Scott / Ray /All forum members / experts are welcome. Please share your experience or knowledge.

Thanks in advance to all.

Mukesh

Mr. Mandeep / Scott / Ray /All forum members / experts,

Waiting for your valuable opinions on the subject matter.

Mukesh

Hi Mukesh

Please refer DR moss (third edition), procedure 2-7 design of flanges, note -10 (page 53) this indicates, we have to convert external loads and moments into equivalent internal pressure.

PV-Elite does the same when there is a wind loads on the equipment

Hope this helps

MVK Srinivas

Hi MVK Srinivas,

If you will properly check the PV Elite does not do the same for wind loads or any other loads. If you got some external loadings then you need to enter the same manually. But if external loadings is based on wind then I dont think so we should apply on body flanges.

i have an experience with this before, my client insist me to put in the wind moment in flange design (only able to do it manually key in). It will thicker the flange of course. They concern about the flange leakage when subject to such external wind load. I don't increase the allowable by 20% anyhow.
My thinking of this is although it was an occasional case, you have to take care of such loadings as well.

Thanks kkchong for your opinions and sharing of your experience.

Friends,

Please share your suggestions and experience.

Mukesh

Mukesh,

Since you have the weight load acting on the flange assembly, which is keeping the 2 flanges together and is actually helping the design you can ignore this axial load to be on the conservative side.

Now, to account for the moment on the flange the typical method used is the equivalent pressure method. There is a method in the new (2007 Ed.) Div. 2 code that is more accurate and less conservative than the equivalent pressure method.

So, you could model the flange using the Div. 2 approach as well.

You may measure the actual dimensions of the flange to see if there is an excess thicknesses that you can take advantage of.

If the seating case is controlling, sometimes using little weaker bolts can help. But, the bolts should be adequate per the analysis.

Check the gasket factors, they play an important part in it.

There are other options too, such as advanced flange design using EN1591 (not too sure about the std.) or finite element analysis using a software such as AxiPro.

I hope this helps.

Thanks Mandeep,

I have already proposed design per ASME Sec VIII Div-2 to my client for the acceptance. As we can not design flanges for external loadings per Div-1, then taking U-2(g) reference Design per Div-2 is the perfact option. In my opinion, that is the best option available from design side.

Thanks for your views.

Mukesh