Open pipe, static pressure, jet reaction

[TPJ07]

I would like to model a pipe with welded elbows, which receives water from a pump and jet it in atmosphere.
The pipe is loaded with internal residual pressure, load due fluid velocity and jet reaction.
When I apply only the residual pressure on the internal surface of pipe and albows, the model is not stable.
I mean, the residual pressure (static) is applied by the program as an external load, like jet reaction....

 

[PetieSmo]

Have you applied displacement constraints to the pipe to prevent it from "flying away"? This could be a source of your instability.