API-650 Tanks - Limitations on non-annular plate bottom

[MJCronin]

I need some information on API-650 tank designs with annular rings.

As I understand the rules, API 650 mandates an annular ring when the stress in the bottom course are above a certain level and higher strength materials are required in the shell. The Brittish standard (BS 2654) and many others mandate an annular ring when the tank is over a certain diameter (12.5m for BS 2654)

Is there anything wrong with an API-650 tank that is of large diameter (say 20-25m)that does not use the higher strength shell materials ?

Stated another way,when writing an API-650 design specification is it a good idea to mandate both the 12.5 m rule of the Brittish standard and REQUIRE an annular ring design ?

Thank you for your time

 

[IFRs]

API 650 Apendix M also has annular plate requirements, but I would not say that a 12.5 M tank needs one (it's a small tank!).

 

[JStephen]

Agreed, a 20-25m tank is NOT a large tank. I am not aware of any reason at all to require an annular ring on a tank of that size if not required by the standard involved. The vast majority of tanks in that size range don't have them.

 

[uncletank]

We tend to use thicknened annular rings only when required for high strength steels, for seismic uplift as per APX E for and APX M when required.

We have used annular rings on smaller tanks i.e 12m in the past where the ring is the same thickness as the remainder of the floor just because it can be easier to fabricate, than the joggle detail.

The only reason I could see a tank of 12m diameter requiring an annular ring would be due to seismic uplift.