46 CFR § 38.10-15 - Safety relief valves—TB/ALL.
(a) Each tank shall be fitted with or (subject to approval by the Commandant) connected to one or more safety relief valves designed, constructed and flow tested for capacity in conformance with subpart 162.017 or 162.018 of subchapter Q (Specifications) of this chapter.
(b) Safety relief valves conforming to subpart 162.017 of subchapter Q (Specifications) of this chapter may be used on tanks for a maximum pressure of 10 pounds per square inch gage. Safety relief valves conforming to subpart 162.018 of subchapter Q (Specifications) of this chapter may be used for any pressure.
(c) The safety relief valves shall have a combined relieving capacity to discharge the greater of the following with not more than 20 percent rise in pressure (in the tank) above the maximum allowable pressure:
(1) The vapors evaporated by an ambient air temperature of 115 °F. plus the maximum flow rate of the cargo filling pipes or,
(2) The vapors generated under fire exposure computed using the formulas of § 54.15–25(c) of subchapter F (Marine Engineering) of this chapter.
(d) The safety relief valves shall meet the arrangement and inspection requirements of § 54.15–25 of subchapter F (Marine Engineering) of this chapter.
(e) Means shall be provided to protect nonpressure vessel tanks from excessive external pressure.
(f) Void spaces between the primary and secondary barriers of nonpressure vessel type tanks shall be protected by relief devices. The relief setting shall not be higher than the void test pressure, and shall not exceed 90 percent of the setting of the safety relief valve protecting the primary tank.