Furnace piping for North Sea offshore

Hi Experts,

I am reviewing a calculation on a furnace piping which is sited in the North Sea.
North Sea projects require accelerations to be considered in different combinations of accelerations in 3 components (X,Y and Z)which is to be considered throughout the entire system.
Furthermore, snow load is to be considered on exposed pipes in uniform load manner.
Lastly, part of the furnace piping have extended surfaces which are to be considered in a uniform load manner for simplicity.
As Caesar is only limited to 3 uniform load cases for U1, U2 and U3, is there a way to input acceleration, snow load and uniform loads due to extended pipe surface in a simplistic manner?
Kindly advise.

There are several options, but I remember the following for now:

1. you may change the density of pipe for the exposed pipes to consider the additional masses.
2. you may use the insulation weight area to add the new masses for the exposed area, if you do not have insulation. In case you have insulation on the piping you may change the density of the insulation to consider to total mass for the exposed area.
3. If things get complicated you can use both options.

Additionally, consider the wind exposed pipe diameter as the ice coated pipe diameter (I guess your snow load is the ice coating on the pipe).

Don't forget to record what you are doing and report in the analysis for verification purposes.

You can also use multipliers in the load case editor... E.G. 2*U1, U2, U3, or 0.707*U1+0.707*U2 to get intermediate directions e.g. Northeast if U1 is North and U2 is East. -U2 would be West.

Mojo,

I'm not an expert but I literally just had to resolve this issue 2 days ago. Take a look at the responses to my post as I think they can clear things up for you as they did for me. You can find it here:

http://65.57.255.42/ubbthreads/ubbthreads.php?ubb=showflat&Main=15452&Number=67698#Post67698

I disagree with changing the density of the pipe or insulation weight as suggested above since this approach would unrealistically increase your SUS load case and that error would be propagated to your SUS + OCC (which is a code stress check requirement...what code are you designing to?)

Fiden4; I disagree with your comment, the snow load (I called it ice coating, see above. The location is given as North Sea and I assume my approach is quite close) may be almost permanent sustain load at some locations, not an occasional load. Therefore your approach to this load may be on the unsafe side. The piping codes do not address this issue directly, therefore you need to use your engineering fundamentals.

mojo;I trust that the acceleration issue can be solved using U1, U2 and U3 for the occasional load cases, and I don't have to be involved in detail.

The third option can be to use the insulation cladding area only for the ice coating by changing the thickness and density, in case there is insulation on the piping. If there is no insulation, I guess, adding insulation information for the ice loading.

Please remember that ice coating will not leave the pipe easily with the platform/ship acceleration of piping if not heated adequately. The details are not given and our discussion is very limited.

Ibrahim, you are correct from the view point of the piping being in the North Sea and that likely the ice load maybe almost permanent as you said.

But in general for areas where the weather has seasons that permanent situation is no longer valid. How then do you handle correctly showing those loads? I would imagine it's how it was described in the post I referenced. Which is how I did it. And by all means, I would love to hear a different option because like I said earlier I was just dealing with this a few days ago so if there is a better mouse trap I definitely want to know.

Fidens4,

All things in perspective: If your area (not that Florida necessarily does) has seasons that could result in the piping being iced for even "only" 2 or 3 weeks out of the year, I would consider this a sustained load.

Occassional loads are more geared towards transient effects such as transportation loads, hurricane wind gusts, earthquakes, relief loads, etc.

All Experts:

Additional supports can not be provided for inetrnal tubes for rediant section operating at about 1100 Cels degrees, so code stress check for seismic cases is not qualified by means of equivalent uniform force according to B31.3.
Any advice or instrction is highly apprecited.

Gino,

It would probably be beneficial to start a new thread.

Let's assume supports cannot be added.
Increasing thickness of the tubes will likely also be a large ordeal.
Then rule out isolating the tubes from the earthquake.

Thanks a lot, isolating the tubes while qualifying seismic cases maybe acceptable, as furnace tubes are governed by API530,which does not take seismic loading into account.

If a tube rupture does not represent an immediate risk to life, health, and environment, I think this would be acceptable, though the end user may wish to entertain what level of seismic event would likely result in such, and is worth chasing down for additional funding for analysis.