API-650 - Max. Loads on Tank Shell Openings

[freixial]

Hello everyone,

I'm modeling a piping system where I have to know the loads on a tank nozzle due to the piping connection.

The model is defined as well as the data for the type of tank and nozzle, so that CAESAR II can give me the maximum allowable loads, stiffness coefficients and its deflection and rotation. API-650 considerations were made.

According API-650, Appendix P, the only important force and moments are the radial force at tank and its circunferencial and longitudinal moments. However, whatching the values given by the run analysis it seems that longitudinal force and radial moment are also important. (??)

Another thing I do not understand yet is when I run the analysis the forces and moments given on the nozzle node are only due to the piping connection or already includes the loads due to the internal pressure and thermal expansion (??)

The refered appendix tell us how to determine the relation between external loads, internal pressure and thermal expansion. Does the programm do it by itself or do we need to get the values after run it and than calculate them?

Would be great if anyone could help me.

Thanks in advance.
Freixial

 

[richay]

Watching the values given by the run analysis it seems that longitudinal force and radial moment are also important. (??)

You would have a big problem if you could torque the nozzle out of the tank, or shear it out of the plate. The moments and radial load would exceed their limits first.

The forces and moments given on the nozzle node are only due to the piping connection or already includes the loads due to the internal pressure and thermal expansion (??)

If you included the (API-650) computed displacment and rotation in the model, then the answer is "yes".

The refered appendix tell us how to determine the relation between external loads, internal pressure and thermal expansion. Does the programm do it by itself or do we need to get the values after run it and than calculate them?

If you mean "does c2 generate the nomographs - the diamond and the triangle" - no it doesn't.

Richard Ay
Intergraph CAS

 

[freixial]

Hi Richard,

thank you very much for your answer. It was very helpful

Best regards
Freixial

 

[stressfan]

Can we use this Caesar modelling method for Tank diameter less than 120 feet?

 

[freixial]

According API-650, Appendix P, the procedure should only be used to tanks larger than 36 m in diameter. But I think if you define a smaller diameter in the API-650 nozzle routine (in Caesar II) the analysis will be the same.

 

[richay]

Yes, you can model this in CAESAR II. The only thing questionable is the "limit computation", which according to Appendix P is only valid for tanks in excess of 120 ft.

Richard Ay
Intergraph CAS

 

[freixial]

Hello everyone,

following the messages above, I have run the analysis bellow:

1)Created a piping system;

2)Define a tank diameter above 36m and its nozzles connections;

3)Run the analysis. Took the radial force, the circunf. and the longitudinal moments;

4)Ploted that figures in the nomographs.

QUESTION 1: The ploted values are so closed to the point (x;Y)=(0;0) that makes me wonder if I am doing everything well done. Am I (??)

QUESTION 2: API 650 appendix P, tell us how to calculate the maximum values (radial force, circunf. and longitudinal moments) however these values are not used to compare with the values obtained by CAESAR II, once we have to plot them in the diagrams. So, what for are the maximum values determined by API 650 (??)

Thank you all, in advance.
Freixial

 

[richay]

Those values that you refer to as "maximums" are not "absolute maximums". In reality, these are the limit points on the axes of those nomographs.

So:
- that radial force limit is the maximum ONLY IF both the circumferential and longitudinal moments are zero.

- that longitudinal moment limit is the maximum ONLY if both the radial force and circumferential moment are zero.

- that circumferential moment limit is the maximum ONLY if both the radial force and longitudinal moment are zero.

Richard Ay
Intergraph CAS