liquid seal overpressure protection 1

[SLuyckx]

Hello,

We have several tanks protected for overpressure and vacuum by a liquid seal. The system consists of a small pipe in another pipe with a larger diameter and a closed bottom end. In case of overpressure the liquid will move upwards and at a certain overpressure the gas start flowing through the liquid .

Two questions arise about this particular system of a liquid seal:
1. Is there an engineering standard to calculate the capacity of a liquid seal used for overpressure protection?
2. What is de the maximum allowed accumulated pressure for vessel with 0 psig design pressure? ASME Section VIII Division 1 cannot be used since it is only applicable for pressures above 15 psig.

 

[Chance17]

Question 1: I am not aware of any engineering standard to calculate the open vent rating.
Thus said, you should use well established pipe friction calculational methods such as Crane Technical Bulletin 400.
OSHA requires a 100% safety factor for uncalibrated pressure protection devices.
So if the rating calculation result is 1,000 scfm, you can only claim 500 scfm of protection.

Question 2: Low pressure tanks have zero allowable accumulation.
Equipment shall not exceed the MAWP or vacuum.
For your situation, I would pay a mechanical engineer to evaluate the tanks for pressure and vacuum.
Get a documented rating for record files.
This is part of being a responsible equipment owner.

 

[Duwe6]

RE: Question #2. Per API-650, the internal pressure can only EQUAL the weight of the roof. For a typical 3/16-inch thick roof, that gives an MAWP of 0.7 Ounces-per-Sq. Inch. The prudent, industry standard set pressure for tank relief vents is 1/2 [0.5] Ounce-per-Sq. Inch. That makes an extremely short water-column -- 1.15 inches. Thus it is not really practical to have a liquid seal-off, but it is marginally possible.

Hopefully, this is an API-620 Low-Pressure tank, but with a design pressure of "0", it is unlikely.