API 620 & 12F Pressure/Vacuum Rating?

[tr6]

We have a number of tanks that were built to API 620 & 12F a number of years ago. The design paperwork has been lost and we need to assign a pressure/vacuum rating. So, how does one do that?

I am thinking that you would need to go through the inspection and testing portion of each of the applicable specs: prepare design calculation, material verification & thickness, NDE, leak test. Obviously the welding procedure cannot be reviewed.

I don't think we are looking to afix an API stamp to the tanks, but would probably want some sort of "official" blessing, whatever that may be.???

Having never been involved in such an exercise, I don't know if we are heading in the right direction, or if this is an exercise in futility. Any suggestion would be appreciated.

 

[Duwe6]

For your 620 tank, hire an API-510/653 inspector to evaluate and calculate the tank. Or have the Inspector evaluate it, including thicknesses and weld x-rays/ultrasound, and have a Tank/Vessel Engineer calc it. It will be a fair amount of work, both inside & outside the tank, and recalculating the entire tank.

Then have an API-653 Inspector evaluate the 12F tank. Assuming the fabricator followed 12F to the letter, it has a "designed in" pressure and vacuum rating.

 

[JStephen]

API-12F tanks include a standard vacuum rating. If the tanks are stamped for 12F, they should be good for that rating already.

API-620 specifies a nominal vacuum that the tanks are adequate for without further design- I think it's 1" water column, but would have to look in the standard to see.

If all you need to do is a assign a vacuum rating, those numbers should do it- and they wouldn't normally be shown on the nameplate anyway. If you need to achieve some specific vacuum rating, that's a different issue.

Neither API-12F nor API-620 include rules for vacuum design. However, the rules in App. V of API-650 could be applied to any cone-roof flat=bottom tank.