Review static output reports for the new analysis - CAESAR II - Reference Data

CAESAR II Applications Guide (2019 Service Pack 1)

Reference Data
11.0 (2019)

Because the flexibility at the vessel nozzle is the only change to the model, you do not need to perform a thorough review of the results.

Check the sustained and expansion stresses to confirm that they are still below their allowable limits

The highest sustained (SUS) stress is 1282 psi. This is below the allowable limit.

Similarly, the highest expansion (EXP) stress is 14,103 psi (not shown). This is also below the allowable limit.

Check the hanger selection

The software selected a lighter size 9 spring for installation at node 28 for a 904 lb. hot load. For the original analysis, the software selected a size 10 spring for a 1209 lb. hot load. The weight of the piping system did not change, but the new analysis has a reduced longitudinal bending stiffness at the nozzle.

Check the loads at each restraint

Review the Restraint Summary, which is too large to show here.

For the pump discharge nozzle at node 5:

  • The pump discharge nozzle loads reveal the impact of the change in flexibility at node 40.

  • The operating moment about the Z-axis shows the greatest change, dropping to 747 from 5905

  • The shear force in the X-direction has been reduced by 50%.

  • The axial force in the Y-direction has risen from 1556 lb. to 1809 lb. This higher pump load is tied directly to the lighter hanger selection, which was also affected by the WRC 297 nozzle flexibilities.

For the spring support at node 28:

  • In the operating position, the spring now carries 904 lb instead of 1209 lb. This reduction in the spring load returns as an additional 300 lb. load on the pump nozzle. With the spring installed directly above the pump nozzle, increasing the load carried by the spring can reduce the load on the nozzle. For additional analyses, the hanger sizing procedure can be adjusted so that the hanger carries more load and the pump carries less load.

For the +Y support at node 35:

  • The +Y support reveals why the hanger load has changed so much. In the first analysis, the support at node 35 was not active in the operating case. The pipe rested on the support in its installed position, but lifted off the support as it went into operation. The hanger sizing algorithm re-adjusted the spring load so that the spring carries its portion of the system, with the system no longer resting at 35. In this second analysis, the restraint at 35 remains active in the operating position, therefore the hanger at 28 does not carry any additional load from 35. The added longitudinal bending flexibility at node 40 allows the pipe to rest at node 35.

For the vessel nozzle at support 40:

  • The support definition at node 40 shows the changes inherent in the WRC 297 nozzle flexibility calculations. Flexibilities are added in the axial and bending directions (Z, RX, and RY), while the shear terms (X, Y, and RZ) remain rigid. This added flexibility greatly reduces the bending moments about the X- and Y-axes at node 40.

The reduced loads result from modeling refinements, not design modifications. If the vessel nozzle connection meets the requirements of WRC 297, you can gain much from nozzle flexibility.

Show the displaced position of the piping system in its operating condition

The imposed thermal growth of the nozzle (in the original analysis) was removed from node 40 and redefined at node 6000. When you compare displacements at node 6000 and node 40, you can see the impact of the nozzle flexibilities. Circumferential bending flexibility (RY) and longitudinal bending flexibility (RX) play a large role in the weight distribution of the system.

You now must reanalyze the pump discharge nozzle loads to see if they meet the allowable limits of API 610.