Re-rating a tank from 1966

[tr6]

We have a tank that was built in 1966 to API 620 for 10 psig. We want to re-rate it. So, I start looking at the design details and discover that the top compression ring does not match any of those shown in Fig 5-6. It actually looks like one in API 650 F-2, detail "k".

My question is: can I use detail "a" from 620 and just increase the size, and thicknesses, of the external angle to match what we've got?

 

[JStephen]

I would say that Detail K of API-650 would be covered under detail d of API-620, using wc for the thickened plate.

If adding area, watch the centroid location requirement, which can limit what can be done.

Also, check API-653, and see if the re-rating must be per the current standard or can be per the original standard. There may be changes required in anchor bolts, foundation sizing, etc. In particular, the interaction of wind, seismic, and pressure have been modified through the years in 650, and I assume in 620 also.