Pressure thrust for AES HEX process inlet and outlet nozzles 3

[FPPE]

Hello,

Our customer asked us to include pressure thrust in external loads on nozzles calculation in accordance to WRC 297 for inlet and outlet nozzles of a AES Heat exchanger.
We have never include it on calculations and our software has no option to automatically include it.
Could you please explain the basic and the applicability to this specific case with WRC 297?
I have read multiple threads on this on the forum but it seems to be applicable for WRC 107/537.
Thank you in advance

 

[Snickster]

I believe pressure thrust can be considered as just an outward axial load at the nozzle in any program if it is not included as specifically "pressure thrust" input. It acts in the same direction as axial loads at nozzle so can be included in same axial forces, as it has the same resulting effect I belleve. Pressure thrust exists since piping connecting to equipment has a force on the first elbow or directional change which is transferred through the piping axially to the nozzle. An opposing pressure thrust exists in the vessel internally that balances the external piping pressure thrust but it must be transfered through the nozzle and vessel shell at the connection, although there is no net force on the equipment. WRC 107, 297 and 368 give methods for analysis of pressure thrust.

 

[Snickster]

Here is a COADE article on how to handle pressure thrust.

 

[jt1234]

Just pay attention how to use pressure thrust. If you use the full PxA as additional axial force, you will be wrong and you will induce unnecessary reinforcement at he nozzle junction. Read the article from COADE provided by Snickster to fully understand the basic theory.
In short, PxA will be an External force in the piping system acting at the first elbow, not at the nozzle junction nor at the face of flange. By equilibrium analysis, this actual "extra" force at the nozzle junction or at face of flange due to PxA will be reduced dramatically. So if you apply PxA at the nozzle junction or at the face of flange, that is unduly.

It is pipe stress engineer to include pressure thrust in CAESAR II analysis, and then produce loading which already includes the effect from pressure thrust at the nozzle junction or face of flange.
It is vessel engineer to qualify the nozzle junction while pipe stress engineer to qualify the flange rating per UG-44(b) or other approach. I am totally against vessel engineer to perform UG-44(b) if you understand the basic. UG-44(b) shall be written in B31.3.

 

[RVAmeche]

Not sure the correct answer but I'm sure the question arose because in Caesar II WRC 297 evaluation, it contains a check box for "include pressure thrust" or not. My understanding is similar to Snicksters post - this is only required if the nozzle extends inside the vessel and otherwise provides a place for that force to go that is not the opposite vessel wall. If this is wrong I'd like to know too.

 

[GD2]

OP,
My understanding of the WRC Bulletins are the following:
1. WRC 107: Local stresses in cylindrical and spherical shells due to external loading.
2. WRC 297: Local stresses in cylindrical shells due to external loading on nozzles.
3. WRC 368: stresses in intersecting cylinders subject to pressure.

All three bulletins have different objectives and limitations.
WRC 368 is the only bulletin that provides designers with a simple and approximate method for calculating maximum stresses at the cylinder intersection due to internal pressure.


GDD
Canada

 

[FPPE]

Thank you for all the answers.

I would like to specify the following:

We designed the heat exchanger according to ASME VIII-1 by formula and performed the verification of nozzles with API 660 loads with WRC 267.
Considering that we have already used API 660 loads, does it make sense to consider an additional radial load to that already provided by the standard? By doing so, the loads on the shell do not verify in 99% of cases.
Thank you

 

[jt1234]

No you don't. If you do so, you are double dipping and ending up with extraordinary reinforcement which will shock you.
The load is considered the "final load" after pipe stress analysis and pipe stress engineer shall limit the nozzle at the shell junction to that values in the API or any other project spec. It is pipe stress engineer to adjust flexibility to achieve it and if not possible, they shall give you the "actual load" at the junction for you or supplier to run local stress analysis.

 

[FPPE]

Thank you jt1234, we think the same. Piping engineer shall limit loads at shell-nozzle junction considering applicable standard for loads on nozzles, if specified during bidding stage.

 

[GD2]

OP,
Did you say pressure thrust? Why only pressure thrust? WRC 537/297 talks about external loads. External loads can be from thermal loads, sustained load and occasional loads (wind, seismic). Here the sustained load will come from internal pressure and weight.
In WRC, it is termed as ‘Radial Load’ or sometimes ‘Axial Load’.

GDD
Canada

 

[FPPE]

Thank you for the clarification GD2!