Dear all

I am doing piping stress analysis for tank diameter less than 60’. I require nozzle stiffness to improve accuracy of piping load on tank nozzle. As per API 650 nozzle flexibility can be considered above diameter 120’ .
Can anyone suggest how mechanical people find out nozzle stiffness value for lesser tank diameter.
Our previous project client supplied that value.In our new project our mechanical people find it difficult to provide me that data.
Can this data can be extracted from coade TANK software or any other way to calculate that data.

Yes, COADE's TANK software can address these smaller tanks. TANK has a PVP-1279 option allows the program to utilze an alternate method to compute nozzle stiffnesses. This alternate method is based on PVP (Pressure Vessel and Piping) paper 1279 - Stiffness Coefficients for Nozzles in API-650 Tanks, by Lengsfeld, Bardia, Taagepera, Hathaitham, LaBounty, and Lengsfeld.

This alternate method is based on the finite element analysis of a number of tanks, resulting in alternate curves and equations for the determination of tank nozzle stiffnesses.

Thank you Richard


Regards

Habib

I have made nozzle stiffness calculations for 12" nozzle for tank dia. less than 36m. The stiffness values with PVP-1279 and without PVP-1279 are as below:

With PVP-1279:
Radial Stiffness N/cm : 0.758 E6
Long. bending stiffness N.m/deg.: 63.391
circ. bending stiffness N.m/deg.: 83.037
Radial deflection mm : 6.65
Longitudinal rotation deg. :-0.265

Without PVP-1279:
Radial Stiffness N/cm : 0.192 E6
Long. bending stiffness N.m/deg.: 62801
circ. bending stiffness N.m/deg.: 48467
Radial deflection mm : 6.65
Longitudinal rotation deg. :-0.265

From above we can observe that, in radial, long. and circ stiffness values there is very much variation and piping stress is not passing with PVP-1279 values.

Finally we have used the values without considering the PVP-1279.

Question: When we have to consider the PVP-1279? Is these values are correct or is there any bug in the programme ? The values especially the long. beding and circ. bending stiffness values does not look realistic.
Can anybody help on this?

MVK

If you read the "Introduction" at the beginning of Appendix P, it states that this particular Appendix is only valid for tanks in excess of 120 ft (36M) in diameter. Therefore, if you perform these same (Appendix P) computations on tanks less than this limit, the results are "suspect".

PVP-1279 was developed specifically for tanks less than 120 ft (36M) in diameter. You should obtain different results when comparing the two methods.

When should you use PVP-1279? When your tank is outside the scope of Appendix P (i.e. smaller than 120 ft in diameter). As to your results, e-mail your input file (.tki) to techsupport@coade.com so we can verify things with your numbers.