external pressure with 650 or 620?

[Roohol]

Dear All
I am designing an ammonia tank with API 620. I'd like to know if it is mandatory to consider API 650 App.V for external pressure or not?
By considering API 650 App.V it is required to use a top stiffener on the compression ring area.
Regards
Roohol

 

[fegenbush]

API 620 has its own provisions for external pressure. Do not use API 650 Appendix V. A stiffener in the compression ring area may be required based on the details of your design.

 

[chicopee]

Instead of designing such tank, buy a propane tank and convert all fittings for ammonia application