Dear Richard,
Thank you for your response. I am still struggling with the same model and still need a bit of advice.
I modelled the existing system as it is, with displacements at the nozzles of air fin cooler. The nozzle loads are exceeding the allowable per API 661. But this system is operating without problems for years.
So I realised that my model was wrong. Most probably by inputting displacements the nozzles were acting as an "displaced" anchor which is too conservative approach.
The header box (where the pipe ties in to the bundle) is not anchored for the bundle frame but the bolt holes are slotted and the pipe moves the header box freely.
Then I modelled the header boxes of the bundles as big heavy pipes resting on +y supports and consequently loads dropped drastically. I also tried to model bundles as a weightless rigid body, and loads are again very low (below API 661 allowable).
Please advise if any of these approaches are correct and safe, and which one is more accurate?
Best regards
Ranka