Nozzle Load Calculation

[Mithun1]

I have a clarification on an ongoing design and thought it is worth seeking guidance.Iam designing a tall vertical vessel with following configuration.

Bottom - 24'' Flange
Shell
Top - 24'' Flange and Blind Flange

I have modelled a dummy skirt and an inter connecting flange to force Wind calculation in PV Elite.

PV Elite Out put

Cumulative Wind Shear : 17629.5 N
Wind Bending : 62.54E+06 N-mm
Abs Max of the all of the Stress Ratio's : 0.2995
Total Wind Shear on Support : 17629. N

This column is attached to a horizontal vessel via 24'' Nozzle.I had transferred cumulative wind shear (As circumferential Shear force Vc in PV Elite) and wind bending moment (As circumferential moment Mc in PV Elite) to this 24'' Nozzle for WRC 107 calculation. Is it correct?

24'' Nozzle failed due to this applied force. Can I use gusset plate to overcome this force?. If yes, what calculation I can produce for this selection of gusset plate. Is it required to include pressure thrust in above calculation of WRC.

I am not very good in Nozzle load calculations and thought to seek advice from experts. Appreciate your expertise guidance.

Thank you
Mithun

 

[LCeballos]

Can you attach a drawing to clarify?

 

[SnTMan]

Mithun1, is it an option to add a pad to the horiz vessel nozzle? Better than gussets imo.

Regards,

Mike

 

[vesselfab]

well, I missed in your first post, that you were only building the column and someone else was building the horizontal vessel.

i would put a virtual base on the column and get the loads.

i would them send them to the client/user/engineer who is you line of contact. Let him send to the horizontal vessel manufacturer.

You have then done your due diligence. You are not required to design a nozzle on a vessel you are not building. the vessel manufacturer is responsible for his own designs.

 

[SnTMan]

Agree w/ vesselfab

 

[doct9960]

Mithun,

Reading through some of your post in thread794-314087, it seems like you have only done a static analysis. Your column and nozzle have a height-to-diameter ratio that is greater than 15. Have you performed a dynamic analysis and checked for the effects of vortex shedding? The nozzle may also need to be analyzed for fatigue.

I suggest you get the assistance of a structural engineer to give you accurate loads due to wind/earthquake. Also ask a pipe stress engineer to check for flange leakage. If the loads on the nozzle are too excessive, you may have to consider restraining the column with lateral guides, guy cables, or snubbers.

 

[jharris3]

If the flexibility of the horizontal vessel allows your vessel to sway further than your model alone will predict, and/or if the horizontal vessel movement imposes movements on your vessel that are not predicted by your model, then there are more "Code" forces on your vessel to investigate.

That far I agree with doct9960.

However, if your client insists that they have taken these things into account then I also agree with vesselfab.

 

[jharris3]

Now to answer your original question

Gussets will help distribute the load out into the shell of the horizontal vessel, however, since the gussets are somewhat discreet points around the nozzle, the overall benefit may not sufficiently relieve stress in the shell of the horizontal vessel. Or another way of putting it, your loads may be high enough to dimple the horizontal vessel shell regardless of how stiff the nozzle is.

There are usually six loads to load into a WRC calculation, and pressure thrust (or more exactly the net axial load) is one of those loads. (Loads: P(axial), Vc, Mc, Vl(longitudinal), Ml, Mt(torque))

At any rate, if you try a gusset first (I would), you should use the AISC Steel Construction Manual (or a comparable part of Pressure Vessel Design Handbook) to calculate the required thickness of a triangular plate with your maximum combined shear and moment applied to one side of the gusset. If it works then it will relieve the stress concentration between the nozzle and the shell by shifting the stress outward into the shell. Gussets wouldn't really do anything for pressure thrust though.

If the gussets don't work then some other restraint between your vessel and the horizontal vessel would be a good idea (assuming you can't convince the other manufacturer to strengthen the shell there)

Have fun!

 

[Mithun1]

SnTMan - I have added rinforcement. it didnt work.

Vesselfab - Horizontal vessel design is in my scope. Iam confused to assign following values in PV Elite.
Cumulative Wind Shear : 17629.5 N
Wind Bending : 62.54E+06 N-mm
Abs Max of the all of the Stress Ratio's : 0.2995
Total Wind Shear on Support : 17629. N
I had transferred cumulative wind shear (As circumferential Shear force Vc in PV Elite) and wind bending moment (As circumferential moment Mc in PV Elite) to this 24'' Nozzle for WRC 107 calculation. Is it correct?

doct9960 - I have included vortex shedding and fatigue in my calculation (Luckily PV Elite has an option). We can get Wind/earthquake loads from PV Elite. But what confuses is the transfer of these loads to the Horizontal nozzle.

jharris3 - Thanks for your advice. I will look into AISC Manual and will get back to you on any clarification. Is there anything mentioned about gussets in Pressure Vessel Handbook?. I have one written by Megyesy.

Thanks,
Mithun

 

[EngAddict]

For a start if your nozzle is in the shell you should not be using WRC107, you should be using WRC297.

Yes, the transfer of loads sound correct. Don't forget to check different direction combinations since the wind direction is not known.

Since this is a cantilever you should also check the flange is suitable for the loads. Start with an equivalent pressure method.

If the loads on the nozzle are too high you could use an insert plate or a forged neck. You should use FEA to prove the gussets if you go down that path. Is structural bracing of the column out of the question?

 

[vesselfab]

use an insert plate for thicker shell or a thickened shell ring

 

[TGS4]

What is the design/operating temperature. I would stay far, far away from gussets or braces if higher then about 500°F.

 

[GenB]

The main vessel has to be designed for the load carrying the tower, whether is gussets, rings, added shell T. In this case I would consider internal ring reinforcing on the shell and calculate the nozzle for the loadings with extra T on the nozzle and padded.

 

[gr2vessels]

I have a sneaky suspicion that the mentioned 24" flange is a ASME B16.5 flange. It cannot be analysed as per Appx.2 and it will fail in PV Elite analysis. The prove is the low stress ratio.
A 24" flanged nozzle should take a lot more load than 17 kN, so the failure in PV Elite is not due to excessive load.
Again, the wind and seismic loads should be transferred as equivalent pressure, not as forces and moments described above. I would try to design a new pair of 24" flanges per Appx. 2 and compare it with the equivalent 24" B16.5 flanges, just to be on the safe side.
Did you try to send the PV Elite file to Coade/Integraph for a quick review? I'm sure they wouldn't mind to check at least the input data, so you get the confidence of correct basis for design.
Cheers,
gr2vessels