API 620 nozzle and external pressure design

[prasit]

Hi experts,

Please anyone suggest me about API620, as I am quite new for this code.

1. How can I calculate nozzle neck thickness? According to the code, it specifies only min. thk of the neck but nowhere indicate the calculation method.

2. If the tank is subjected to partial vacuum, How can I calculated the required thickness for this vacuum.

Thank you
Prasit

 

[JStephen]

For typical nozzle sizes, the calculated thickness based on pressure will be very thin and the minimum thickness will control. You can calculate the thickness based on pressure using the equations in ASME B&PV Section VII, basically pressure x radius / allowable stress, with some minor adjustment for variation of stress through the thickness. For that matter, you could calculate T-2 for a cylinder as for the tank itself, using the equations already in API-620, with the nozzle radius instead of the tank radius.

I don't think API-650 includes rules for vacuum design. It should state somewhere that tanks built to the standard are good for 1" water column or something of the sort. You could apply the rules from API-650, Appendix V, to API-620 tanks. You could also apply the rules from ASME B&PV Section VIII.