Jacketed piping systems are modeled by running the jacket elements directly on top of the core elements so that the two are concentric.
You can generate a jacketed pipe model by modeling the entire core and then duplicating the core piping using an appropriate node increment (such as 1000). This produces a second run of pipe which is modified to build the jacket model. For the jacket, change the pipe size, temperature, bend radii, and so on, to finish the model. Then, attach the jacket and core by changing the node numbers and adding restraints.
Typically, the end caps connecting the core to the jacket pipe are much stiffer than either the core or the jacket. For this reason, node pairs like (10 and 1010), (25 and 1025), (35 and 1035), and (40 and 1040) are often joined by using the same node for each. For example, the displacements and rotations at the end of the core pipe are assumed to be the same as the displacements and rotations at the end of the jacket pipe.
Internal spiders offer negligible resistance to bending and axial relative deformation. Node 15 might be connected to node 1015 by a restraint with a connecting node. For an X-run of pipe, rigid restraints would exist between the two nodes for the Y- and Z-degrees of freedom.
The +Y support acting on the jacket at node 1020 does not cause any stiffnesses to be inserted between 20 and 1020. Node 20 is included in the model so that the outside diameter interference can be checked at the 20-1020 cross sections. If there is any concern about interference or interference-related stresses at the 20-1020 nodes, then you can use restraints with connecting nodes and gaps to approximate the pipe-inside-a-pipe with clearance geometry.
Because CAESAR II constructs the jacketed piping model by associating nodal degrees of freedom, the software does not know one pipe is inside of another. Therefore, consider the following items:
If both the jacket and the core are fluid-filled, the fluid density of the jacket must be reduced to avoid excess (incorrect) weight.
If wind or wave loads are specified, the wind or wave loading must be deactivated for the core so that the core does not pick up the load.
The core pipe should probably have its insulation thickness set to zero.