How's the offset nozzle modelled and analysed in CAESAR II ?

For info : There is a 4" pipe nozzle on a 2000mm dia vessel with the nozzle offset from the center by 300mm.

Regards

Sri

to add..

The vessel is horizontal and the nozzle is vertically upwards with a 300mm offset to the longitudinal axis of the cyl. vessel ( non radial)..

I'd just run a dummy rigid element from the vessel centerline to the point where the nozzle connects to the surface. (You're not analyzing the vessel, you just want to transfer forces and moments properly, and account for the thermal growth of the vessel.) There are examples in the applications guide, the only difference between these and what you have is that the dummy rigid will be skewed.

Your reply has made me clear reg. the approach to be taken.

However, I was assuming that the location and the profile of the connection between the vessel and nozzle should impact the flexibilites at that point(as should the dia. and thickness of vessel)...can you clarify.

Thanks Regards,

You are getting mixed up with what Caesar is capable of. The flexibilities at the nozzle shell interface are beyond what a 2D beam element program can calculate. Best look at PD5500 or EN 13445 for that. Treating the nozzle as a 'anchor' means that any loads we calculate should be absolute maximums. Any local flexibilty should help reduce the loads [assuming the loads are not primary in nature]. The other thing to remember is that the local loads will need to be transformed so they are normal to the shell at the interface for analysis or comparison to allowables. If you look at the local forces report for the element from the vessel centerline to the shell/nozzle interface that should give you the transformed forces.
Also if you are doing the local load calcs have a look at PD5500 ApG2.8 or EN13445 - they both contain a method of calculating the local stresses without resorting to graphs, and are therefore easy to do a Mathcad worksheet for.

Kenny,

Thanks for the explanation...

Now I know what CAESAR can do and where to get the loads for checking the vessel Nozzle.


Thanks and Regards,

Yes and No. True CAESAR II uses the "3D Beam Element", which is essentiall an infinitely thin stick - so there is no sense of volume or surface. The "3D Beam Element" is good for "system analysis", not "local analysis".

However, within the Piping Input module, you can define nozzles (and their associated parameters), and CAESAR II will use the indicated bulletin to compute the flexibilities at that point. The bulletins supported here are: PD5500, WRC297, and API650.

Richard,
I have used before the Nozzle definition in CAESAR as per WRC297...However I have not seen any provision to input the offset nature of the Nozzle w.r.t vessel (i.e almost going back to my original question).

If i model the rigid element as skewed, does CAESAR take care of the difference in the connection...(sorry, i'm shooting the question without actually making a comparison of the 2 options )

Thanks and Regards

No, because WRC297 doesn't do that.

Richard
While Caesar can include the nozzle flexibilities, I was trying to empahsise that it is perhaps not good practice to include them too early in the analysis especially if you are not hugely experienced in this work. I am sure the old Kellogg book contains a warning on this matter. Treating the nozzle as a fixed anchor initially and working towards a solution from there often results in a much better understanding of the system and hence a more apprpriate solution. When you are really up against it or the job demands that such conservatism is avoided, then the nozzle flexibilites can be brought in to help you.
An analogy would be that to calculate the spring constant for each fixed pipe support and use that right at the start of the analysis to help reduce the restraint loads would be regarded as being excessive instead of using the absolutely fixed supports that Caesar supplies [1e12N/m is it?]. It is a proper thing to do if you really are struggling but is rarely justified.
As ever engineering judgement must be used when applying any technique.

Agreed.