MAWP of API 12A tanks/ IFR ?

[avgguyfrom85]

Good morning all, I hope all is well. I have been tasked to investigate the MAWP of 70,000BBL tanks built to API 12A (old riveted tanks, IFR with shell). The tank has low pressure relief devices on the floating roof set at minimum for the pressure (0.5 Oz) and vacuum (O.5 Oz) to protect the seal when emptying the tank completely.

Q-1: Is it commonly seen to have low pressure relief devices on IFR?
Q-2: Will the shell of the tank be subject to API 2000?
Q-3: Opinions on determining the MAWP of API 12A tanks?

Your time and advice is greatly appreciated. Thanks,

Avg

 

[IFRs]

IFRs need pressure and vacuum relief, I set them to less than the weight of the IFR
IFR seals do not need pressure / vacuum relief - they are not that tight or sensitive
API 2000 does not apply because IFR tanks should have circulation vents, see API 650 Annex H
MAWP for an IFR tank should be atmospheric, because of the circulation vents

 

[avgguyfrom85]

Thanks for the prompt reply!


Have you seen any case in which a shell has been constructed with out circulation vents?
If so, the shell would either be protected by Emergency Vents and/or frangible roof joints I presume?

Thanks again,

Avg.

 

[IFRs]

In the USA, IFR tanks either have circulation vents or are gas blanketed. In other countries IFR tanks are designed as fixed roof tanks with conservation vents and emergency vents. If the tank has no circulation vents then it should have suitable vents for normal operations and also emergency conditions if the top joint is not frangible.