Wind Load Calculation - Vertical vessel with No Skirt

[Mithun1]

Good Afternoon,

I have a situation to design a Vertical Column (9m Height approx) attached to a 22inch (custom design) Nozzle of a Horizontal vessel. Our scope is limited to the supply of vertical column which will be installed to horizontal vessel at site.

My queries as follows.

1) How does PV Elite calculate wind loads in the absence of Skirt/Legs.

2) Wind loads as per British Standard Institute Code of practice CP-3,Chp V,Part II. I understand this has been replaced by BS 6399. How do I convert following requirements (As per client spec) to BS 6399 code. iam not very good with wind codes frown
Wind Speed FactorsS1 & S3 - 1
Wind Speed Factor S2 in accordance with CP-3, Ch Pt II,Table 3 and Class B.

3) What additional measures shall I consider in designing such a Tall Column with out skirt/legs.


Regards,
Mithun

 

[gr2vessels]

Hi Mithun1,
Your column is attached to the supporting structure by a flange. The flange can take a certain load, calculated as hydrostatic load and additional 'equivalent pressure' due to external loads, like wind and seismic loads. The PV Elite allows you to include the equivalent pressure.
I suggest you take an advanced training course to use the PV Elite or ask someone experienced in pressure vessel design to complete the calculations. It is a dangerous situation you to perform a design beyond your capacity of understanding the basics of PV design and design codes requirements. If the vessel fails and kills someone, you end up in jail (rightfully).
Cheers,
gr2vessels

 

[Mithun1]

Thanks gr2vessels for your advice. My question was as advice on calculating Wind Loads. PV Elite, to my understanding, does not perform wind calculation in the absence of Skirt/Legs.

Anyone experienced in Pressure vessel design & worked in PV Elite respond to my query please...

Regards,
Mithun

 

[MJCronin]

So..... as I understand this situation.

The existing horizontal vessel takes all of the loadings from the new vertical coulumn through an interconnecting process flange ?

The supports both components are the supports for the horizontal vessel ? Is that correct ?

What possible process reason could there be for such an odd arrangement ? (a response of "that what the client said" is not acceptable)

Why are these two components not independently supported and connected by piping ? This is accepted configuration in 99.99% percent of the world.

My opinion only

 

[chicopee]

About submitting a hand sketch so that I can fully understand the setup between the two tanks because right now I am attempting to visualize your description.

 

[Mithun1]

Let me shed some light to the configuration. Horizontal vessel is used as a Reboiler and Vertical vessel as a still column connected to the reboiler via 22'' Nozzle. Reboiler is separately designed and U Stamped. Still column (Vertical Vessel) needs to be designed separately.

Attached configuration for this vertical vessel.

http://files.engineering.com/getfil...90-a0c9-4d92baf9d44c&file=Vertical_Vessel.pdf

MJCronin - I am not sure of the support you are discussing. There are no support for this vertical vessel. It is bolted with Horizontal vessel.

 

[SNORGY]

Mithun1:

If your scope of design is from the vessel flange up, would there be anything wrong with assuming a "hypothetical skirt" of closely similar dimensions to the vessel nozzle (by OTHERS) below the mating flange? That way you can get reasonable results for your column design and communicate reasonable loads to the OTHERS for their nozzle design. What is the contractual design scope split?

Alternatively, you could model the whole vessel and then treat the vertical column as a uniformly loaded (by wind) vertical cantilever. That might be enough to give you a loading condition, from which you could use hand calculations and the Code to check the design.

Have you tried posting this question in the COADE CAESAR II forum?

Regards,

SNORGY.

 

[jamesl]

This is more like a PV Elite specific question. I agree with SNORGY. You can add a mock up skirt or leg to the piece, a good PV design software usually list the wind loads at the bottom of each component. You can get the result at the bottom of your flange or right above it, which should be close enough for flange loading.

 

[doct9960]

Mithun1,

I agree with SNORGY and jamesl about assuming a hypothetical skirt to get the nozzle and flange loading.

If you are getting very large moments at the flange that would cause leakage, you might want to consider some lateral restrictions or guides near the top of the column. Your column is quite tall for such a small diameter. I'm guessing your column is around 30 ft.

 

[Mithun1]

Thank You all for your responses. I had modelled a Dummy Skirt and Dummy mating flange to get wind load calculation. I was not sure if it was an acceptable solution.

SNORGY - I had posted this in PV Elite forum (COADE) and didnt get any response. I guess PV ELite forum is not as active as before. Engineering Tips rocks...

Regards,
Mithun

 

[chicopee]

Computer programs are fine however looking at your column, you could do some hand calculations for wind and seismic loads and compare with the programing results.
You have two nozzle connections on your column, about looking into flexible connections as I would guess there will be some serious movement at the top of the column.

 

[Mithun1]

chicopee - I have done manual calculations as per the guidelines set in Pressure Vessel handbook. Results are comparable.

Now I have another issue in transfering these loads to Horizontal Vessel Nozzle (Where this vertical column is connected). Nozzle fails WRC calculation due to excess Loads/Moment.

Is it unusal to weld ''Gusset Plates'' to this Nozzle. I need some guidance for the selection of Gusset plate. Is it acceptable as per ASME Section VIII Div 1?. WRC 107/297 does not provide any calculation using Gusset Plates. Help me please....

 

[MJCronin]

Show us a sketch with both the vertical axis vessel and the Horizontal vessel.

Show all locations where the assembly is supported and the types of supports.

All of the reboiler/process columns that I have seen have seperate vessel supports and interconnecting piping.

Explain why yours must be different

 

[vesselfab]

You can build a virtual support and transfer the loads to the horizontal mounting flange.

you can also, model a virtual vertical extended nozzle on the horizonal vessel to check you results.

does not take long to model this stuff.

 

[jharris3]

Even though in the end you need to provide calculations for only your vessel, why not model what you know of the horizontal vessel including its supports and apply the wind loads to it all as one?

Then hide the output for the vessel below your flange, or extract your calcs from the rest?

Wouldn't this also help you more accurately identify the height of your vessel above its actual support which is the saddles on the horizontal vessel? Then the selection of some restraints might also be more appropriate.

Don't know if that is helpful, i'm a Compress user.

 

[gr2vessels]

Hi Mithun,
I'm back on deck.
As you noted, the PV Elite doesn't help with your configuration, but it does help with designing the bottom pair of flanges per Appx 2. You need to calculate the equivalent pressure due to the wind forces and moments acting on the Still vessel, the PV Elite accepts the equivalent pressure for sizing the flanges. You don't need fake skirts and gusset plates, just a good understanding of the equivalent pressure definition. Thousand of deaerators have been designed with this method in the world, including U-stamp.
Cheers,
gr2vessels

 

[nsbreddy]

Perfect answer from gr2vessels. I would calculate the equivalent pressure and apply as external presure in the software (i am a compress user). Software is a tool and you should simulate the load condition to get the desired results....

 

[doct9960]

Using equivalent pressure to design the flanges is probably okay, but how do you analyze the local stresses on the vessel shell itself? You will need the wind loads (shear & moment) and the weight of vertical column in analyzing the local stresses on the vessel shell.