MODELLING TRUNNION WITH CAESAR

[psapiensone]

I want to outline a discussion about the trunnions installation in elbows using Caesar.
They are very well-known the methods of verification of stress in trunnions (for example using the Kellog method), but this items aren’t the main thing in this discussion.
I understand that in many cases isn’t necessary to model the trunnion, but for this discussion to consider only cases in that it’s necessary.
This post it seeks to begin a discussion about as modelling correctly trunnions connected to elbow, taking in consideration; loads, diameters, materials and other parameters that consider important.

Regards,

Pablo P.

 

[C2it]

The Kellogg method applies best to a straight pipe connection althouhghit is used for elbow connections.

It is known to be conservative for straight pipe when the ratio of pipe to trunnion is small. Arguably since the load path (weld length) in an elbow trunnion is far greater, stresses under comparable conditions should be less than straight pipe. The risk with a large ratio of pipe to trunnion is that local shell flexibility will allow large local stresses to act. Equally there is no doubt that a trunnion on an elbow will reduce its flexibility and therefore the related s.i.f and this may be taken into account.

A comprehensive approach would be to use FE-pipe or similar in conjunction with Caesar, establishing flexibilities etc in an FE-pipe run for inclusion in a Caesar model. A simple approach would be to model the elbow as a simple 90 deg. change of direction thus no extra flexibility, manually add the appropriate s.i.f to be conservative and avoid a large pipe / trunnion ratio. Include the trunnion itself if it is significant. Then use Kelloggs if you want to.