Number of safety valves on liquefied hydrocarbon storage tanks

Article 5.1.4 of GB/T37816-2019 \"Selection and Installation of Safety Relief Devices for Pressure Equipment\": Two or more safety valves should be considered for parallel installation in the following situations: a) To ensure the safe operation of pressure equipment, or when it is necessary to maintain or replace safety valves while keeping the equipment in operation, two safety valves along with a rapid switching device for these valves should be installed, ensuring that each individual valve can meet the required safety relief capacity for the pressure equipment; b) When a single safety valve cannot meet the actual relief requirements of the pressure equipment, two or more safety valves should be installed; c) In special operating conditions where there is a risk of failure of the safety valve itself, at least two safety valves should be installed. Article 5.3.9 of the \"Design Code for Liquefied Natural Gas Receiving Stations\" (GB51156-2015): 5.3.9 Liquefied natural gas storage tanks shall be equipped with safety valves and backup safety valves. \"Guidelines for the Implementation of Safety Standardization in Ammonia Synthesis Enterprises\" AQ/T 3017-2008 5.5.4.6 The safety management of liquid ammonia filling and storage processes in enterprises shall meet the following requirements: c) Liquid ammonia storage 3) Liquid ammonia storage tanks with a surface area of over 100 m2 shall be equipped with dual safety valves, and the exhaust from these safety valves shall be directed to a recovery system or to a flaring system for combustion ； JB/T 12130—2015 \"Design Code for Liquid Ammonia Supply System in Flue Gas Denitration\", 6.6.2.6: The liquid ammonia storage tank shall be equipped with 2 safety valves, and 2 isolation valves shall be installed in front of each safety valve. Article 6.2.4 of the \"Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems\" SH/T3007-2014: 6.4.2 d) The safety valve of pressure tanks shall be equipped with an online standby safety valve and one safety valve bypass line. One full-bore isolation valve should be installed in front of and one behind the safety valve, and the symbol LO (seal removed) should be indicated on the design drawings; according to the \"Design Code for Process Piping Systems in Refining Plants\" SH/T3122-2013, section 20.3, a backup safety valve should be provided in any of the following situations, with the number of backups determined as n+1 (where n is the number of safety valves required for calculation purposes): a) There is a history of leaks in the safety valve ； b) When the safety valve is blocked ； c) When the medium is corrosive: d) When the medium tends to form scale ； e) When online maintenance or online inspection is required ； f) There are other fault records that affect the performance of the safety valve. 20.4 When there is a backup safety valve, isolation valves shall be provided at the inlet and outlet of the safety valve. The inlet and outlet isolation valves of safety valves in normal operation should be sealed with lead or locked in the open position; the inlet isolation valve of the standby safety valve should be sealed with lead or locked in the closed position, while its outlet isolation valve should be sealed with lead or locked in the open position. 20.5 A backup safety valve may not be required in any of the following situations, but a shut-off valve shall be installed at the outlet of the safety valve, while no shut-off valve is necessary at the inlet ； a) Installed on batch production equipment: b) Installed on equipment that can be detached from the operating system ； c) Installed on the equipment for materials within a device that can be emptied. Article 6.2.4 of the “Code for Process Design of Safety Pressure Relief Devices in Petrochemical Plants” SHT3210-2020: 4.6 For safety valves whose operating medium is viscous, highly corrosive, or highly toxic or of even higher hazard level, backup safety valves should be provided; these backup valves shall have the same specifications as the main safety valves in use. Article 5.3.1 of the \"Safety Management Specifications for Liquefied Hydrocarbon Tank Areas\" TCCSAS 016-2022: 5.3.1 Liquefied hydrocarbon storage tanks shall be equipped with online standby safety valves. The installation of safety valves shall comply with the relevant provisions of TSG 21. Manual full-bore isolation valves should be installed before and after the safety valve; the flow area of these isolation valves must be at least equal to the cross-sectional area of the safety valve’s inlet and outlet. They should remain in an open position during normal operation, and should be sealed or locked in place.

The number of safety valves on liquefied hydrocarbon storage tanks depends on the specific **standards and the design requirements of the tanks. The relevant standard in China is GB50074-2014 Design Code for Oil Depots, which specifies the design requirements for safety facilities of liquefied hydrocarbon storage tanks. To determine whether 2 safety valves must be installed, it is necessary to consult the specific regulatory requirements and the design parameters of the tank. Redundancy and reliability are typically taken into account during design, and multiple safety valves may be installed to ensure safety even if one of them fails. It is recommended to consult a professional design firm or review the relevant design specifications to determine the required number of safety valves. .

Appendix B of GB-T 12337-2014 \"Steel Spherical Storage Tanks\"

Check to confirm whether it is a major hazard source; the levels are required to be different. But I haven’t heard of any requirement for two safety valves either. There should be safety valves; atmospheric storage tanks are equipped with flame arresters on their vent valves. Where a nitrogen seal is required, there must also be pressure relief manholes. This is generally how it is in my case

Two settings are required; please be aware of this.