Hi,

I have to conduct a stress analysis for a hot tapping (conection of a new cold system to an existing hot system without shutt down).

Coade published a paper on this subject by 1996. If I understand the paper well, there are 3 steps to perform the analysis using CAESAR II.

- Create a model with the new system at installation temperature and the old one with operation T. Include nodes on restraint locations but omit the restraints.
- Run a T1 OPE analysis and copy the diplacements for every location for the appropiate boundary condition.
- In a new file, now with all the restraints included, copy the displacements obtained at step 2 in the corresponding cnodes, but only those for the boundary condition restricted.

This method looks suitable when the new system is short or small. For more complex systems, for instance a 50 meters run pipe with no anchors in between, I think thnigs are not so simple. If I release all the restraints in the new system, the vertical displacement will be huge!. maybe 50 meters or more.

I think that's not the point of the paper. I would suggest to release only the horizontal restrictions of the header, so it will move freely draged by the old system. At the vecinity of the conection, some vertical restraints can be removed.

Can anyone give me some advice on the subject?. Are my reflections wright?.

Thank you for your help


Hot tapping paper

alfonms,
You need to check the displacements and rotations in T1 only case. There is no weight involved. The T1 only case will show the displaced location of nodes under the given temperature profile. Since weight is not involved you should not get huge vertical displacements.
In new model, the displacements are applied at restraint points/nodes that were selected earlier as CNODE (new model implies to the same Caesar file with new name and temperature profile applied to complete system along with restraints).

Thank you Rajinder,

You are right. I forgot to remove W from the OPE case. Now it is clearer.

Regards,