Nozzle trust load due to internal pressure should not be considered as the extarnal load.

[mechengineer]

Continuing with: thread794-472852
Share experience on opening reinforement, nozzle load and trust loads to know that nozzle trust load due to internal pressure should not be considered as the extarnal load to analyze by using WRC537/297 or FEA.
1. Div.1 UG-37 opening reinforcement is a simple way of opening area replacement subjected to internal pressure (IP). It is worth noting that in low pressure, the required area of reinforcement from UG-37 is larger than Div.4.5. A certain degree of external load is satisfied when the IP and opening reinforcement are satisfied. But UG-37 is not able to apply for the nozzle loads/stresses analysis.
2. Dv.2. 4.5 opening reinforcement method (pressure area) is that assume the area force (P* area) divide by the affective metal area as the local primary membrane stress and shall not exceed 1.5S.
The max. local primary membrane stress Pl subjected to internal pressure is from Div.2 formula of (4.5.55) plus the Pl+Pb subjected to the external force shall not exceed Spl that seems to make it possible to combine the external force and opening reinforcement together to analyze the local stress at the opening. It is not true. It is only applicable for opening reinforcement, not for the local stress analysis in detail. Pl from formula 4.5.55 is too high for local stress analysis.
3. WRC297 is for analysis of local primary membrane Pl stress and bending Pb stress subjected to external force only without considering IP.
4. PVE Lite uses a general primary membrane stress (Pm) subjected to IP plus the local stresses (Pl+Q) (by using WRC 297) subjected to the external piping load to assess the stress intensity. It does not considered the local primary membrane stress subjected to internal pressure because it is not available except use FEA.
5. Div.2, design by analysis and use FEA tools, so far it is the most accurate and perfect way to combine all loads, IP (note: ‘pressure trust load’ is not an independent external force, it is derived from IP), external force, thermal load… together to assess the local stresses intensity for the opening of shell with a nozzle loads.
6. Take the sample I did to show the comparison of the maximum stress ratio between WRC297 and FEA (NozzlePro). Vessel: 2774_ID x 15.88t_SA516Gr70. Nozzle: 12” sch.60_SA106B. DP=0.93 MPa, DT=299 deg. C. Nozzle loads: P=-14400 N, Vc=10800 N, Vl=14400 N, Mc=8640 N-m, Ml=11232 N-m, Mt=12960 N-m. Software used: PVElite 2020 & NozzlepPro 2019.
WRC297: Max. stress ratio is 87%
NozzlePro: Max. stress ratio is 68%
WRC297 + pressure thrust load: Max. stress ratio is 166%. (note: the pressure thrust load will be very huge for a big size of nozzle).
It is obviously that WRC297+trust load is too huge and far away from the FEA analysis result of NozzlePro.
Hence using WRC297+trust load is incorrect. I raised SR (support request) to PVELite, the funny answer is ‘to keep trust load option is just because it may be comfortable for those older uses to check the design did by older versions of PVElite.’ Can’t image how mamy such options have been outdated or incorrect in PVElite, like Appendix 10 as well ……

 

[BJI]

..nozzle load and trust loads to know that nozzle trust load due to internal pressure should not be considered as the extarnal load to analyze by using WRC537/297 or FEA

I see this more of a software usage question, no the PVE option should not be checked. Historically I believe this approach was used in an attempt to account for the lack of stress concentration around the opening. If you are working to WRC 297 then follow that method, including all limitations, and check that you have adequately accounted for the pressure stresses around the opening. If you are using software, understand what modifications they have made.
For FEA, if I don't have a cap on my model I will apply pressure thrust as a load, this is required for equilibrium and to achieve the appropriate stresses in the nozzle neck and junction. Pressure thrust is not an external load.

For DBR, nozzle reinforcement is a separate requirement that must be satisfied.

Can’t image how mamy such options have been outdated or incorrect in PVElite, like Appendix 10 as well ……

I assume you mean appendix 1-10, not quality control systems. Appendix 1-10 was superseded by the method in division 2, they should just update the option to use the updated method.

 

[XL83NL]

Aren’t thrust loads only considered per WRC 368 for large manways and openings/nozzles with blind flanges?

Huub
- You never get what you expect, you only get what you inspect.

 

[mechengineer]

@BJI,
That has to see how the FEA software apply the internal pressure load into the model (for a partial of pressure vessel case), whether the FEA software considers the internal pressure load in all possible directions within a closed boundary. if not, the FEA may not be able to provide a true pressure load into the model. The shape of nozzle to shell junction is complex, if FEA does not consider a pressure load with closed boundary, we can't imagine how correctly to apply internal pressure to the complex model.

 

[mechengineer]

@XL83NL,
I think that WRC 368 may be for piping system only, not pressure vessel. For a long pipe may cause an expansion due to internal pressure (so called 'trust load') whcih need to consider for piping engineer to arrange pipe support or extension bellows.
For mayway/blind nozzle/instrument nozzle on pressure vessel are witnout nozzle external load at all, so it does not need to check nozzle external load on the vessel.

 

[XL83NL]

I think 368 is for vessels

https://files.engineering.com/downl...f45-99d8-b1666473d14d&file=20190612104747.pdf

https://www.eng-tips.com/viewthread.cfm?qid=295291

Huub
- You never get what you expect, you only get what you inspect.

 

[mechengineer]

@XL83NL,
Sorry that I misunderstood WRC368 talking about thrust load.
Yes, WRC368 is for the stress analysis of the intersection of nozzle and shell due to internal pressure, but not the thrust load.
The correction on my previous reply is that the thrust load due to internal pressure may only consider for piping system. For a long pipe may cause an expansion due to internal pressure (so called 'trust load') whcih need to consider for piping engineer to arrange pipe support or extension bellows.

 

[BJI]

WRC 297 is generally conservative for stress in nozzle necks, except when circumferential bending stresses are significant, since the method specifically excludes nozzle circumferential bending stress (refer WRC 297 section 3.1). Ultimately it is up to the user to ensure the method used is appropriate, or at least conservative relative to a more accurate solution.

It is my understanding that WRC 368 was specifically developed considering internal pressure and pressure thrust, therefore, additional thrust loading would not be appropriate.

By FEA I mean using software such as Abaqus, where the analysis is performed in accordance with the model configuration. For software like NozzlePro, you can verify that it is including the 'thrust load' by comparing the longitudinal stresses away from the junction to hand calculations.