Check the static load cases - CAESAR II - Reference Data

CAESAR II Applications Guide

PPMProduct
CAESAR II
PPMCategory_custom
Reference Data
Version_CAESAR
12

After error checking the model, review the load cases.

  1. Click Edit Static Load Cases on the CAESAR II Tools toolbar, or click Edit > Edit Static Load Cases.

    The Static Analysis - Load Case Editor dialog box displays.

    CAESAR II begins with a standard set of load cases based upon the piping code selected and the loads defined in input. For this tutorial, the software includes load cases to size the hanger before performing the standard structural and stress analyses. The hanger sizing algorithm requires two analyses before analyzing the standard load cases:

The operating condition for this analysis consists of the dead weight of the pipe, its contents and insulation, the design temperature and pressure, and the preload on the hanger at node 28. The installed condition includes the dead weight and hanger preload. In addition to these structural analyses, certain stress conditions must be addressed.

For the piping code, the sustained and expansion stresses must be calculated. Sustained stresses include dead weight, preloads, and pressure. Sustained stresses can be taken from the installed condition analysis if the pressure loads are included. CAESAR II includes the pressure term in the installed case because pressure, in most cases, has no impact on the structural loads on the piping. With the installed case structural analysis also serving as the sustained case stress analysis, no additional load case must be added to calculate the sustained stresses.

Expansion stresses reflect the change in system position from its installed position to its operating position. Because of system non-linearity, this change in position cannot be determined by analyzing thermal loads alone.

By default, CAESAR II constructs a third load case to calculate the expansion stress (range). This case is not a third, complete analysis of the system. Instead, it is a product of the operating and installed structural analyses already performed. The difference in system displacements between these two cases is the displacements stress range from which the expansion stresses are calculated. The third class of stress in piping – occasional stresses (as opposed to expansion and sustained) – is not included in the recommended analyses and must be specified by you. Likewise, Fatigue (FAT) stress cases are provided only when specifically required by the active piping code (TD/12, for example).

For most systems, the recommended load cases are exactly what you want to analyze.

L1 (W) - Weight for hanger loads

Calculates the dead weight carried by the proposed spring at node 28.

L2 (W+D1+T1+P1) - Operating for hanger travel

Calculates the vertical travel of the proposed spring. All load categories, which compose the operating load case, are used for this analysis. These are dead weight, displacements, thermal set 1, and pressure set 1. With these two numbers—the load carried by the hanger and the amount of travel it must accommodate—The software selects the appropriate spring from the Anvil catalog. This spring and its proper preload are installed in the model for the remaining analyses.

L3 (W+D1+T1+P1+H) - Operating case condition 1

Defines the operating hanger load case. L3 is identical to L2 but includes the sized hanger preload (H). This analysis produces the operating forces and moments on the supports, and the deflections of all points in the system. L3 is a structural analysis case and not a B31.3 stress analysis case. The refining piping code does not recognize pipe stress in the operating condition as a test for system failure and does not establish a limit for this state of stress.

L4 (W+P1+H) Alternate sustained stress based on operating condition 1

Provides an alternate method for the sustained case of L5, using the restraint status from the L3 operating load case to evaluate the stresses induced by primary loads.

L5 (W+P1+H) - Sustained case condition 1

Defines a structural and stress case of a cold system. The load case eliminates the (assumed) thermal effects (D1+T1). By including pressure (P1), this case also has the necessary components to be used to report the system’s sustained stresses.

L6 (L3-L5) - Expansion case condition 1

Defines an algebraic combination of two basic load cases. The displacements of L5 are subtracted from the displacements of L3 to produce these results. This case develops the displacement range of the system in its growth from the installed position to the operating position. This displacement range is used for the calculation of the system’s expansion stresses.