API-650 Tank Re-rate Questions 1

[Grant C.]

Hello!

First time poster. I'm relatively new to the fixed equipment scene and have been tasked with re-rating 18 API 650 above ground storage tanks(all manufactured around 1976) from around 3"WC to 4.7"WC design pressure. My current approach is to model each tank as it is currently in AMETank focusing on the shell, roof, top member, bottom, and anchor chairs utilizing the original design parameters. Then I will take the tanks that pass with the increased design pressure and conduct B-scans to identify any corrosion issues.

I cannot find a step by step path to re-rating storage tanks in 650 or 653. API 510 has something similar in section 8.2 but I am hesitant to just follow it.... is my approach sufficient? Most experts I talk to in my company cannot provide a straight or sufficient answer.

Cheers,
Grant

 

[JStephen]

Your results could be highly variable depending on tank dimensions, etc.
A major issue is that the older API-650's didn't necessarily require an overturn check for wind, or that wind loading be combined with internal pressure. This has been revised as time went along, but has seemingly changed each addition/revision also.
So you may potentially have tanks that don't meet current design criteria for the pressures they were actually designed for, never mind any increases.
And in other cases, it'll be no problem.
I'm not familiar with AMETank so can't comment on particulars there.
Note that in the current Annex F, if you're over a certain pressure, additional detailing requirements kick in for roof openings, etc.
Also note that older anchor bolts tend to be L or J shaped bolts, while newer anchor design guides downrate the capacities of those considerably.

 

[Grant C.]

@JStephen I'm taking account for the wind overturn in the tank software. Using 125mph wind here in south Texas. I've only had one tank come back so far with some anchor chair warning (too few). So I'm trying to figure that out within code as well. I hate winging this kind of stuff because it always comes back to bite me in the MOC process and hopefully never with any future failure.