Overfilling Protection for Weak Tanks

Low pressure tanks, designed to API-650 & API-620 code of construction may be subject to the overfilling scenario. Existing codes such as API-2000 do not give enough guidance to calculate the flow through a conservation vent or low pressure relief device. Small amounts of liquid static head may overpressure the tank and can result in catastrophic failure. Generally, conservation vents are used for the normal thermal plus pump displacement requirements. The flow rates are typically reported in SCFH of air and are generally available in all vendor catalogs. The flow rate of liquid is not reported and is not available in the literature. This paper proposes to show the calculation methdology using conventional hydraulic methods to design an appropriate sized vent to handle the overfilling over pressure scenario for low pressure tanks.