Stress Analysis - Tank Nozzle

[tatvamasi]

Hi

while doing Stress Analysis for the Piping located in Tank Nozzles, should we consider the Center Line of the Tank as the Fixed point/ Anchor point or the Location of the Bolts in the Periphery of the Tank, which actually holds the Tank.

 

[BigInch]

I would use the nozzle weld point to the tank shell, unless you expect to have a horizontal thermal growth of the tank or vessel (that you can reference to the vessel centerline or to an anchored end support) that will deflect your piping.

http://virtualpipeline.spaces.msn.com

 

[JStephen]

If you cansider the nozzle/shell intersection as a "fixed" point, you may be off considerably on the pipe calculations. There is some flexibility in the shell, and also both radial movement and rotation from product in the tank. API-650 App. P includes some guidanace on the issue.

Typical stresses in an oil tank are 20-25,000 psi, which will give about a 1/2" of radial movement on a 100' tank. Low nozzles will see less of this movement, but more rotation.

 

[DSB123]

tatvamasi,
You need to take everything that is appropriate into consideration in your stress analysis. If the tank changes temperature then there will be thermal growth (expansion/contraction) which will be theoretically from the centre of the tank and upwards/downwards from the base of the tank. If the nozzle is close to the bottom of the tank then during filling/emptying of the tank the tank will "bulge" and give both radial deflection and rotation. These effects need to be considered to ensure that the loads on the tank nozzle are calculated correctly. As the nozzle is located in a "thin" walled tank shell then it will have flexibility. These flexibility factors need to be introduced into the calculation also. See API 650 Appendix P for the methods of calculating the "bulging" effects and the flexibilities of the shell providing that your tank falls under the geometric limits.

 

[MJCronin]

Suggest that you investigate this question on the COADE/CAESAR-II bulletin board.

http://www.coade.com

-MJC