Dear all,

We are performing the stress analysis of a new steam system (400ºC,30 bar) to be connected by means of a tie-in to an existing pipe system.

My problem is that we don't know if when the new steam pipe is erected the existing one is going to be in operation (hot) or during shutdown (cold) and that fact can affect the stress analysis. The new system is going to be mounted without any kind of cold spring or similar (so with no deformation).

My question is which is the best method to simulate all those cases in CAESAR since we have different scenarios:

- Both systems mounted during shutdown ("usual" analysis with which I don't have any problem)
- Old system in operation (hot) when the new system is mounted (cold). How to model it? In this case, during a shutdown there will be expansion stresses in both pipes...

Thanks for any help.

Best regards

There's a good article on hat taps stress analysis by John Luf in October '96 Coade news letter. That will give u a good idea...

Calculate the old system displacements,analyze the new system seperately with the displacement & impose end reactions obtained from this analysis to old system & do another analysis & make sure existing supports are not overloaded beyond maybe (20%)thats my gut feel.

It seems that either the closure weld of proposed system will be made via a hot tap or it will be made with the existing system shutdown. I would meet with the operations and contractor (if determined), explain why it is important to know the method of connection, decide which method will be used, and then model that. Be sure to note the assumption of the method of connection to the existing system in the construction contract and/or drawings and state the impact on design if the method is changed in the construction phase.

Thank you all.

Very useful that article by John C. Luf in Caesar newsletter. I have been reviewing it and trying to apply it to my system, when I have found a problem.

In my system , the new pipe connects to a boiler which has got thermal displacements son I must consider those displacements but at the same time I have to input the dispalcements due to the existing system. I don't know wich is the right way to do it. Any idea?

Regards

You will want to check the tie in loads on the existing pipe, so add it to your model. Use T2 for the temperature of the existing pipe and T1 for the temperature for the new pipe. Then use the load cases to check all cold-hot, hot-cold, hot-hot, cold-cold combinations.

Regards, John