| Applies To | |
| Product(s): | AutoPIPE Nozzle |
| Version(s): | ALL; |
| Area: | Load cases |
| Date Logged & Current Version | May 2020 |
Problem:
When should the "Include Pressure thrust in GR, Hy case" be used in AutoPIPE Nozzle?
Solution:
After enabling this checkbox the application will calculate a radial pressure thrust load acting on the vessel. This load equals the Gravity load plus the Design Pressure times the inside diameter of the Nozzle:
Example:
Radial Press Thrust for Gr (Gravity)
Where:
Grload = Load due to GR load case acting in axial direction of the nozzle (in this example:Load tab, GR load case, X-axis)
P = Design Pressure (System Tab)
Do = Nozzle Outside Diameter (Nozzle Tab)
t = Nozzle Wall thickness (Nozzle Tab)
Compare to the Output report:
As seen above, the hand calculation matched the reported value. This radial pressure load is then used by the program when calculating code stresses.
Question: What happens when additional load cases are considered? How does this affect the Radial Pressure thrust load ?
Answer: Results are based on the combinations under consideration. Another words, it all depends on the combination.
Example: Consider the following load cases and combinations.
Load cases = Gr, P1, T1
Combinations = Gr, GrP1, GrP1+T1
Radial, P load Results:
Notice that the Radial P load changes based on the loads in the direction of the nozzle axis only.
Gr = -7885 - 100 = -7985
GRP1+T1 = -7985 - 200 - 300 = -8485
GrP1 = -7985 -300 = -8285
In summary, if "Include Pressure thrust in GR, Hy case" combination option is enabled, a PxA force is calculated and added to the existing Radial load due to Gravity. Thus, whenever Gravity (Gr) load case is used in a combination, this Grload+(PxA) value is added to the other load case radial loads to calculate a total Radial load for use in code stress calculations.
When importing loads from AutoPIPE, note that the load due to pressure only (P1..Pn) was calculated based on the thick wall formula for Pressure extension. However this load can be affected by adding additional concentrated forces that were combined with pressure cases (P1..Pn). These concentrated forces can represent influences from any number of sources. Instead, it has always been suggested to add a single User load case (U1..Un) that represents the total of all other influences, besides pressure, acting on the nozzle. That way AutoPIPE Nozzle can create combinations as needed for the user to easily understand the results (ex. GrP1+T1, GrP1+U1, etc..).
With all but one change, the same behavior and calculations for Gravity occurs for a Hydrostatic (Hy) load case. The only difference being a Hydrotest Pressure factor will be applied to the Design Pressure. This factor can be found when pressing the Options button on the System tab. The user enters a value that is multiplied by the Design Pressure. This new value will then be used to calculate the PxA radial load as indicated above. Again this factor would only be applied to the Hy load case and not the Gr load case.
To answer the question, When should the "Include Pressure thrust in GR, Hy case" be used in AutoPIPE Nozzle? As clearly shown above, this option provides a Users the ability to capture pressure thrust load at the Design Pressure value. If this is not a requirement in your analysis, than do not enable this option. However, if your analysis requires stress values at a nozzle to consider both pressure thrust due to Design Pressure and Pressure load case (P1..Pn), enable this option and review operating condition combination results as needed.
Final comment, the user must fully understand the various values on the Load's tab, what they really represent, and how they were calculated before generating combinations and results with AutoPIPE nozzle.