Redesign the piping system - CAESAR II - Reference Data

CAESAR II Applications Guide (2019 Service Pack 1)

PPMProduct
CAESAR II
PPMCategory_custom
Reference Data
Version_CAESAR
11.0 (2019)

As discussed in Review the model, the large X-moment at the pump discharge nozzle (node 5) is caused by the thermal expansion of leg A (from node 35 to node 40) working against the stiffness of legs B and C. If the thermal strain of leg A is fixed, only the system stiffness can be changed to reduce the operating load at node 5. You can reduce this stiffness by adding an expansion loop or an expansion joint. For this tutorial, you will add an expansion loop.

The best location for an expansion loop is determined by the orientation of leg A, which creates the excessive thermal strain. The added piping to generate the expansion loop lies perpendicular to leg A. For this system, pipe can be added in either the X- or Y-direction. This added pipe effectively increases the cantilever length which is displaced by leg A. By increasing the cantilever length, the stiffness is reduced and loads drop.

There are several conditions which set the loop size:

  • Available support location

  • Maximum distance between supports

  • Cost of pipe

  • Available space

For this tutorial, you will add an eight-foot by eight-foot loop of pipe and an additional support on leg A in the X-direction. For systems that are not analyzed, the recommended maximum spacing between supports for 8-inch water-filled pipe is 19 feet (see ASME B31.1 121.5 or MSS SP-69). The 8-foot loop run lengthens the 30 - 35 pipe from 12 feet to 20 feet, which is close to the recommended spacing.

Modify existing elements in the model

When testing layout modifications, you should save the existing model as a new file and leave the original model intact. If the proposed changes do not produce the required results, the original model is still available for the next attempt. You then do not have to delete the proposed changes from the model.

  1. Return to the main window ribbon, and click Home > Input > Piping Input with Tutor-B2 as the current model file.

    The Classic Piping Input dialog box and a graphic view display.

  2. Click File > Save As, and give the model file a new name of Tutor-B3.

  3. Click Next Element repeatedly to advance through the model to display element 30-35.

    You can also click on element 30-35 or use Find Node to go directly to the element.

  4. In the DX box, type -20- to change the element length from 12 ft. to 20 ft. Press TAB.

  5. Click the Restraints box to display the Restraints tab on the right.

  6. For the +Y restraint, change Node from 35 (the node at the end of the elbow) to 33 (the node at the beginning of the elbow).

    • The recommended maximum spacing, a conservative guideline, of 19 feet for an 8-inch pipe limits sag between supports to 0.1 in. With the restraint at node 35, the distance to the node 28 hanger is 21 ft. Moving the restraint to node 33 decreases the distance to 20 ft., closer to the recommended maximum.

    • The maximum distance between supports as specified in ASME B31.1 and MSS SP-69 ensures a very low sustained stress in the line. Because CAESAR II calculates the sustained stresses, the output confirms that much greater distances than the recommended maximum between supports are safe.

  7. Click Break .

    You can also right-click the element and select Element > Break Element.

    The Break at Element dialog box displays.

  8. Break element 30 - 35 by adding node 32 at the 10 ft. (10-) midpoint, and then click OK.

  9. Click Next Element twice to advance to element 35-40.

  10. Click Break , and add node 135 at 8 ft. (8-) from node 35.

Add a new elbow at node 135 to begin creating the loop

  1. Double-click the Bend check box to display the Bends tab on the right.

    The software creates a long radius elbow (1-1/2 times the nominal pipe diameter), node 133 at the elbow near point (Angle 2 of 0.000), and node 134 at the midpoint (Angle 1 of M). Node 135 moves to the elbow far point.

    The elbow is part of the horizontal pipe run, but does not display until you create the horizontal pipe run.

Insert an 8-foot element after the elbow

  1. Click Insert Element , select After to place this new element after element 35 - 135, and then click OK.

    The From node changes to 135.

  2. In the To node box, type 235.

  3. In the DX box, type 8- (for 8 ft.), and then press TAB.

    The software creates the last element of the loop. The last element of the pipe remains in its original location.

Add an elbow and adjust the From node for the final element

  1. Double-click the Bend check box to add the bend at node 235.

    The software creates a long radius elbow (1-1/2 times the nominal pipe diameter), node 233 at the elbow near point (Angle 2 of 0.000), and node 234 at the midpoint (Angle 1 of M). Node 235 moves to the elbow far point.

    Again, the elbow is part of the horizontal pipe run, but does not display until you create the horizontal pipe run.

  2. Click Next Element to advance to element 135 - 40.

  3. In the From node box, type the value of the new node, 235, and then press TAB.

    The software attaches the new loop to the last element of the pipe.

Add a support to the new element 135 - 235

ASME B31.1 and MSS SP-69 provide limits to spacing between supports when bends are included, such as for this expansion loop. The maximum support spacing for 8-inch carbon steel water line is 19 ft. The maximum run of pipe is 3/4 of the straight run limit. For this model the limit is about 15 feet. There are over 26 feet of pipe between 35 and 40, so a new support is required.

  1. Click Previous Element to go back to element 135 - 235.

  2. Click Model > Insert Restraint , or right-click the element and select Restraint > Insert Restraint.

  3. Insert the restraint by adding node 140 at 5 ft. (5-) from node 135. In Copy Restraint from Node, use the same +Y support as used at node 33 to create a new support with the same properties at node 140.

    The software breaks the element and inserts the new restraint.

Adjust the sizing of the hanger at node 28

A large vertical load remains on the pump nozzle after the hanger at node 28 was sized by the software. The spring selected in Tutorial A from the 1 - ANVIL hanger table can carry more of the dead weight of the pipe and valving. You will adjust the sizing algorithm, so that the pump nozzle carries no load when the software calculates the load to be carried by the larger spring.

  1. Click Previous Element to go back to element 25 - 30. Click Hangers to display the Hangers tab on the right.

  2. In the Free Restraint at Node box, type 5.

  3. In the Free Code list, select 1-Y.

    The software disconnects the vertical Y restraint at node 5 while it calculates the dead weight load carried by the proposed spring at 28, allowing the spring to carry the full vertical load.

  4. To save the model, click Save or File > Save.

  5. As a final check, click Distance . Select Between Element Nodes, type 5 (the first element) and 40 (the last element) in the boxes, and then click Calculate. In Results, the length should be 26' 8 3/8", the same distance you measured in Tutorial A.

Your model redesign is complete!