Pressure relief systems
Each cargo tank with a volume exceeding 20 m3 is to be fitted with at least two pressure relief valves of approximately equal capacity, suitably designed and constructed for the prescribed service. For cargo tanks with a volume not exceeding 20 m3, a single relief valve may be fitted.
If cargo holds with independent tanks may be completely closed, overpressure/vacuum relief valves are to be provided for in order to avoid pressure variations of more than 0,15 bar above and below atmospheric pressure.
Interbarrier spaces are to be provided with pressure relief devices complying with recognized standards.
The combined relieving capacity of the pressure relief devices for interbarrier spaces surrounding type A independent cargo tanks where the insulation is fitted to the cargo tanks may be determined by the following formula:
- Pressure relief valves are to be connected to the highest part of the cargo tank above deck level. Pressure relief valves on cargo tanks with a design temperature below 0 °C are to be arranged to prevent their becoming inoperative due to ice formation when they are closed. Due consideration is to be given to the construction and arrangement of pressure relief valves on cargo tanks subject to low ambient temperatures.
- Valves are to be constructed of materials with a melting point above 925 °C. Consideration of lower melting point materials for internal parts and seals shall be given if their use provides significant improvement to the general operation of the valve