Nozzle loads 1

[McJe]

On a vertical tower we have several nozzles, let's say 30.
On every nozzle we have loads (forces and/or moments)

WRC can calculate the effect of these loads to make sure the nozzle is strong enough.

But, how are all those loads influencing the vessel design?
Because of all the different places, heights and angles the nozzles are located, it becomes really hard to check if the vessel wall isn't overstressed due to these loads.
Even harder, what do these loads mean together with wind and earthquake design?

You could say, don't engineer the vessel so the thickness is at it's limit. Correct, that's what we do.
But what if it is an engineered tower, where the customer changed specs slightly so the limits are reached?

To calculate is by hand seems pretty hard to do.
Finit element analysis sound like an option.

But how are the calculation/design programs handling these loads? I know Compress, PVElite, ... allow you to enter nozzle loads. Do they only calculate WRC107 with this data? Or are these loads taken in account for the general calculations?

I know,
many questions...

But I was just wondering if someone else has thought of this too...


Jeroen.

 

[SnTMan]

McJe as long as the nozzles are sufficently far apart (about 1/2*sqrt[R*t], as I recall) the loads will not influence each other.

Obviously all external loads acting on a vessel have to be reacted into the world, and if they are significant should be examined.

Does commerical software do this? I doubt it.

Regards,

Mike

 

[jte]

Jeroen-

Chances are that the cumulative piping loading will not influence the design of the vessel shell. I often tell people that the piping is there to hold the vessel up during an earthquake. Just to make ‘em think a bit. I’d suggest that you take all the loads from the 30 nozzles (add platforms as well just for fun), combine them in a worst case approach (i.e. align all nozzles at plant North), then run some quick calc’s to determine the impact of all the loads on the vessel design. Do this exercise once just to get a feel for the magnitude of the loadings.

Having said that… I did have to increase the diameter of the anchor bolts and thicken the baseplate/top ring assembly once, years ago. I vaguely recall that it was a large column, perhaps 10’ diameter x 150’ tall with an unusually large overhead line coming down one side and supported by the vessel. The pipe was probably on the order of 50% of the vessel diameter.

I would increase Mike’s criteria to at least 2*sqrt(R*T), but generally agree with his comment on local influences.

jt

 

[SnTMan]

the piping is there to hold the vessel up during an earthquake

I love it!!

The 1/2*sqrt[Rt] is probably more like the decay length, so, you'd want your nozzles spaced at least TWICE that. Pretty rusty on this advanced stuff

Mike

 

[TGS4]

Actually - the decay length is about 2.5*sqrt[Rt], and yes, you'd want your nozzles spaced @ twice that.

Completely agree with jte's assessment of the influence of all of the nozzle loads on the entire vessel design. Once you do that worst-case scenario, you'll see that the impact is small. Furthermore, that scenario is likely never to occur, and the piping loads will probably cancel each other out at any particular point in time.

 

[vesselguy]

I love SntMan's comment as well about piping there to hold up the vessel. I have to remember that. Most Piper thinks vessels are anchor points for piping so they impose super large loads on my vessels; its insane!!

When I last do this sort of detail calculations at Fluor, we did add the "significant" piping forces to the wind/seismic moments for shell thickness and skirt/base calcs.

No. You don't need to do FEA for this. Please.. people, don't use FEA for everything. Just use basic engineering priciples.

 

[TGS4]

vesselguy - you're right about not using FEA for this. It's a simple hand-calculation.

 

[jte]

Geez... how many "ex Fluor" guys are involved in this discussion?

jt

 

[DSB123]

vesselguy,
Totally agree about not using FEA for such calcs. I think it's the new graduates coming out into the "real" world who think everything has to be done with FEA instead of the "olde" reliable manual methods that have been used for decades.

 

[SnTMan]

vesselguy, credit where its due, that was jte.

Add in that the piping loads most probably have a (possibly large) thermal expansion component, which is even less likely to have any effect on the vessel as a whole.

DSB123, not to be offensive or anything, but I am afraid many of the new grads CAN'T DO the hand calcs, thus the first resort to FEA.

Regards,

Mike

 

[JStephen]

Consider how the force gets there as well. What's the other end of that pipe attached to- something perfectly rigid, or something even more flexible than the vessel? Or is it connected to pipe that is then braced off of the vessel itself?

You'd also have to consider the pressure across the opening or lack thereof in calculating the net force on the vessel.

 

[DSB123]

SnTMan,
That's exactly what I was meaning. New Grads using a "sledgehammer" to crack a nut. They know no better than to turn to FEA and computers when all that is needed is a calculator and some basic principles. If they can't do the hand calcs how are they going to verify the FEA solution by approximate methods? You must always check that you have not used GIGO when using FEA and computer software.

 

[SnTMan]

DSB123, yes I understood your meaning quite well

Regards,

Mike