Modeling the second half of the jacket is more complex than the first half because the jacket only covers the straight runs of piping. For this reason, the jacket elements are coded manually, as opposed to any form of duplication. Although duplicating portions of the model is feasible, the time required to delete the jacket from the elbows is greater than the time required to input only the straight sections. By modeling the jacket directly, the restraints for the spiders can be input as you encounter them.
To start entering the necessary data in the Classic Piping Input dialog box, press Ctrl + End to go to the last spreadsheet in the model. At this point, click Continue and change the node numbers to 2600 and 2610, with a DX of 5 ft. Where is the element from 2600 to 2610? Return to the spreadsheet and temporarily change the diameter of nodes 2600 to 2610 to 24-inches and try the volume plot. The element 2600-2610 has been positioned at the plot origin because, at this time, it is not connected to anything. Return to the dialog box and correct the diameter by changing it back to 12-inches.
To properly connect the jacket to the core, you must add restraints at nodes 2600 and at 2610. At node 2610, add a CNode of 1610 with restraints in the Y- and Z-directions. At node 2600, add a CNode of 1600. Do not associate nodes 2600 and 1600 in the Y- and Z-directions. Associating the nodes in such a way allows the jacket to move freely in the X-direction and to spin about the X-axis, producing an unstable model. This problem did not exist in the first half of the model because the jacket was continuous over the elbows and the model was three-dimensional in nature. In the second half of the model, you must ensure that the appropriate axial and torsional restraints are applied to the jacket. At node 2600, model an anchor to 1600. This is simpler than modeling separate X, Y, Z, and RX restraints. This causes the 8-inch line to be physically connected to the 12-inch line in all six degrees-of-freedom.
The next jacket element covers the core from node 1616 (the end of the elbow) to node 1640. Node 2615 is anchored to node 1616 with a CNode.
The next two elements, 2620-2630 and 2630-2640, are standard pipe elements with a DZ of -4.333 ft. Each To node is connected to the corresponding core node with a CNode associating the X- and Y-directions.
The remaining three sections of jacket are modeled in exactly the same manner. The final step in the modeling is to add the spring hangers at nodes 2615 and 2655 and the positive Y-restraint at 2135. The completed model is shown in the following figure.
Completed Jacketed Piping System
An example of the completed input file, JACKET._A, is delivered to the [CAESAR II Directory]\Examples folder.
After the input task has been completed, you must error check the job and analyze it for the specified loading conditions. Check the results to ensure that the system is modeled correctly. These checks should include the following:
Verify the weight of the core system, the jacket system, and the combined system. You can use the Sustained Restraint report for this check. Be sure that the jacket pipe fluid density accounts for the volume lost due to the core. Because CAESAR II does not do this automatically; you must reduce the density of the jacket fluid accordingly.
Verify that the piping system does not develop large axial loads in the core, the jacket, or the equipment anchors. This can be caused by improperly over restraining the pipe in the axial direction or by the effects of thermal growth on dissimilar metals.
Check the displacements at the elbows in the operating case and verify that the core pipe does not tend to move through the jacket. CAESAR II does not perform interference checking.
Check the displacements at the spiders where the jacket and the core are connected. In the direction of the spiders, the displacements should be the same for both the jacket and the core.
Verify that wind and wave loads, if any are specified, are disabled on the core piping.
Ensure that the insulation thickness of the core pipe is set to zero.