At 3m and a delta T of 58 degrees your pipe is growing around 2mm. Caesar applies a restraint stiffness of 10^12. In the real world nothing is this stiff. As well there is likely some safety factor in the maximum moment the well head can take. So the difference between the real world results of successful operation and the failure you are seeing in your model is likely a combination of conservative modeling and using up the safety factor in the real world.
If you can show a system operating in the real world you could apply 319.4.1 a) (assuming B31.3 is your code) Nor formal analysis is required if the piping "duplicates, or replaces without significant change, a system operating with a successful service record" The difficulty in using this clause is to get this documented. Ideally you would have the client sign off on something saying we have this arrangement at this site and has been operating without incident for x years. Getting someone to sign off on this and people saying "well its worked before" is a big step.
How have you modeled the well head. Are you just anchoring it in space, How are you accounting for wellhead growth? If you are just anchoring it in space and not modeling the well head that may give you overly conservative results
Edited by Greg F (02/05/09 02:17 PM)
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