Installation of emergency shut-off valves

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I. Definition of emergency shut-off valves
Regarding the definition of emergency shut-off valves, currently there are several standards and specifications that define this term. For example, Article 3.1 of “Emergency shut-off valves for liquefied gas equipment” (GB/T 22653-2008) states: “Emergency shut-off valve: A valve installed on tank trucks, tank containers, storage tanks, or pipelines; under emergency circumstances, it can be quickly closed manually or automatically.” Article 3.1 of “Emergency Shut-off Valves for Cryogenic Media” (GB/T 24918-2010) defines an emergency shut-off valve as “a valve installed on tank trucks, storage tanks, or pipelines, which can be quickly closed manually or automatically in the event of an accident”. Notice on the Interim Provisions for the Safety Technology Management of Liquefied Hydrocarbon Spherical Tank Areas of Sinopec Group Company (issued under Sinopec Safety Document No. 635), Article 2.2: “Emergency shut-off valves: Valves installed on the inlet and outlet pipelines of spherical tanks, capable of being quickly and tightly closed in the event of an accident or abnormal condition. The allowable leakage rate for such emergency shut-off valves shall meet the standards of ANSI B16.104 (FCI 70-2) CLASS V or a higher grade.” The valve shall have the capability to be closed thermally, manually, and remotely via manual control (remote control with a handle).” Article 3.1 of the “Regulations on the Selection and Design of Emergency Shutoff Valves for Spherical Tanks Storing Liquefied Hydrocarbons” (Sinopec Document No. 518) states: “Emergency shutoff valve: A valve installed on the inlet and outlet pipelines of spherical tanks storing liquefied hydrocarbons; it can rapidly and tightly shut off (TSO) and isolate flammable, irritating, and corrosive materials in the event of accidents such as fires or leaks within the tank area.” When the liquid level in the spherical tank reaches or exceeds the high-high level limit, the emergency shut-off valve can be used to prevent the material from overflowing the tank. No other pipe fittings or valves shall be installed between the emergency shut-off valve and the nozzle of the spherical tank, except for connecting pipes; the distance between them must meet the requirements for piping installation, valve maintenance, and process operations. The emergency shut-off valve shall have automatic and manual closing functions; the manual closing function shall include remote manual closing from the control room and local manual closing.” As can be seen from the above definition, in terms of type, any valve—whether it is a gate valve, ball valve, or butterfly valve—can be used as an emergency shut-off valve, provided that it can fulfill the function of shut-off. Furthermore, in terms of function, an emergency shut-off valve is a type of valve that allows for rapid remote shutdown; its purpose is to isolate the flow of material in case of an emergency (such as a fire or leak), thereby preventing potential accidents and containing them within certain limits. II. Setting requirements regarding the emergency shutdown function
The implementation of the emergency shutdown function in any production system must be based on safety principles. That is, through measures such as proper selection of instrumentation equipment, structural constraints (redundancy and fault tolerance), inspection and testing cycles, and diagnostic technologies, the design of safety instrumented functions should be optimized to ensure compliance with risk reduction requirements. Article 13 of the Interim Provisions on the Supervision and Management of Major Hazards of Hazardous Chemicals issued in 2011 (**Order No. 40 of the State Administration of Work Safety**) stipulates that “major hazards classified as Level 1 or Level 2 shall be equipped with emergency shutdown functions,” and that “for key facilities involving toxic gases, highly toxic liquids, and flammable gases among major hazards, emergency shut-off devices shall be installed.” ； For facilities handling toxic gases, install emergency leak response devices. For Class 1 or Class 2 major hazard sources involving toxic gases, liquefied gases, or highly toxic liquids, an independent Safety Instrumented System (SIS) must be installed.” The “Notice of the State Administration of Work Safety on Issuing Opinions on Preventing Major and Extraordinary Accidents Involving Hazardous Chemicals and Fireworks” issued in 2016 (Document No. Anjian Zongguan San [2016] No. 62) further stipulates that “starting from January 1, 2017, all hazardous chemicals storage areas that are classified as Level 1 or Level 2 major hazard sources and lack emergency shutdown (emergency cut-off) functions must be taken out of service.” In February 2022, the Ministry of Emergency Management issued a notice titled “Basic Requirements for Emergency Shut-off Systems in Oil and Gas Storage Enterprises (Trial)”, which sets forth requirements for renovation projects involving emergency shut-off valves on large above-ground atmospheric storage tanks currently in use by oil and gas storage enterprises. The notice stipulates that “emergency shut-off valves must be installed on all process material inlet and outlet pipelines directly connected to the storage tanks.” Several other documents also mention the requirements for implementing an emergency stop (emergency shutdown) function. To implement the emergency shutdown function, an emergency shutdown system must be installed; this system utilizes emergency shut-off valves to ensure the safe shutdown of the production equipment. So, in what situations is it necessary to install an emergency shut-off valve? In summary, settings are required in the following situations: (1) Chemical tank farms that constitute first- or second-level major hazard sources ； (2) Key storage tanks such as large-scale ones, those for liquefied gases, and those containing corrosive and irritating chemicals ； (3) Liquid-phase inlet and outlet of spherical LPG storage tanks ； (4) Facilities such as corrosive and irritating gases, corrosive and irritating liquids, and flammable gases that constitute major hazard sources of level 3 and level 4 ； (5) Inlet and outlet pipes for materials in corrosion-irritating material storage tanks, low-temperature storage tanks, and pressure spherical tanks ； (6) Material inlet and outlet pipes at the bottom of liquefied hydrocarbon storage tanks (non-spherical tanks are also included) ； (7) Loading and unloading pipelines without buffer tanks in the loading and unloading station ； (8) There is also a process shutdown system based on the results of HAZOP analysis/LOPA analysis. III. Selection of emergency shut-off valves Article 10.1.6 of the \"Code for Selection and Design of Automation Instruments in Petrochemical Industries\" (SHT 3005-2016) states that \"when the process requires tight shut-off (TSO) of the control valve or when it is involved in emergency shut-off interlocks, the allowable leakage class of the control valve should be selected as Class V or higher as specified in the GB/T 4213 or ANSI/FCI 70-2 standards.\"” ； Article 10.3.6.7: A fusible plug shall be capable of being installed on the cylinder used in the actuator of pneumatic emergency shut-off valves. The melting point of this fusible plug should be 75°C ± 5°C. When the temperature of the cylinder reaches or exceeds this melting point, the fusible plug melts, allowing the pressure inside the cylinder to be released; this enables the spring on the other side of the cylinder or the compressed air in the air reservoir to push the piston and close the valve” ； Article 10.3.6.14: “The pneumatic actuators and their accessories used for emergency shut-off valves shall have fire protection measures; fire protection covers shall be installed, and these covers must comply with UL 1709 standards, enabling them to resist hydrocarbon fires for 30 minutes at 1093°C”” ； Article 10.3.7.11: “The actuators and accessories used for electric emergency shut-off valves shall have fire protection measures; fire protection covers shall be installed, and such covers shall comply with UL 1709 standards, enabling them to resist hydrocarbon fires for 30 minutes at 1093°C”” ； Article 10.3.7.12: “The power cables and signal cables of the electric actuator used for emergency shut-off valves should be provided with fire protection measures.” Article 6.4.1 of the \"Design Code for Tank Areas in Petrochemical Storage and Transportation Systems\" (SH/T 3007-2014) stipulates that remote-operable emergency shut-off valves shall be installed on the inlet and outlet pipelines for liquefied hydrocarbons at the bottom of liquefied hydrocarbon storage tanks. “The actuator of the emergency shut-off valve shall have fail-safe measures.” Regarding these fail-safe measures, the explanatory statements take the following forms: (1) Use a fail-safe single-cylinder pneumatic actuator ； (2) When using a double-acting cylinder pneumatic actuator, install an emergency air tank ； (3) When selecting an electric actuator, use one equipped with a UPS backup power supply or one that has its own energy storage device. Article 9.4.1 of the \"Code for Installation and Design of Petrochemical Instruments\" (SH/T 3104-2013) states that \"adjustment valves and control valves used for emergency shutdown interlocks do not require isolation valves or bypass valves.\" According to Clause 5.4.1.13 of the “Code for Design of Automation Systems in Petrochemical Tank Farms” (SH/T 3184-2017), “For emergency shut-off valves used to interlock and cut off feed, a local manual valve-closing button or switch shall be installed outside the fire hazard area, so as to allow manual operation in emergency situations.” Item (22) of the “Notice on Further Strengthening the Safety Design Management of Construction Projects Involving Hazardous Chemicals” (AQSIQ General Administration [2013] No. 76) states that “for storage tanks for corrosive and irritating substances, cryogenic storage tanks, and spherical pressure vessels, emergency shut-off devices that can be operated automatically or manually from a remote location shall be installed on the pipelines for material inlet and outlet.” Article 6.4.2 of the “Code for Fire Protection Design of Petrochemical Enterprises (2018 Edition)” (GB50160-2008) states: “When there are no buffer tanks within the station, an easily operable emergency shut-off valve shall be installed on the loading/unloading pipeline at a distance of more than 10 meters from the loading/unloading arms.” By summarizing the above provisions and standard specifications, the selection criteria that emergency shut-off valves must meet are as follows: (1) The actuator used for the emergency shut-off valve and its accessories shall have fire protection measures; a fire protection cover should be installed, and this cover must comply with UL 1709 standards, enabling it to resist hydrocarbon fires for 30 minutes at 1093°C ； (2) Fire protection measures should be taken for the power cables and signal cables of electric actuators ； (3) The permissible leakage class of the shut-off valve shall be selected as Class V or higher as specified in the standards GB/T 4213 or ANSI/FCI 70-2 ； (4) The actuator of the emergency shut-off valve shall have a fail-safe shutdown function ； (5) On-site manual valve closure buttons or switches should be installed outside the fire hazard area ； (6) The emergency shut-off valves for storage tanks containing corrosive and irritating materials, low-temperature storage tanks, and pressure spheres should have automatic or manual remote control capabilities ； (7) For the installation of emergency shut-off valves, isolation valves and bypass valves may not be required. IV. The relationship between emergency shut-off valves and the SIS system. The SIS system (Safety Instrumented System) falls within the category of automation for industrial production processes; it is a system designed to ensure safe operation, and its safety level is higher than that of DCS-based automation control systems. When abnormalities occur in the automated production system, the SIS intervenes to reduce the likelihood of accidents. The SIS system mainly consists of structural sensors, a logic solver, and final control elements; the emergency shut-off valve is one such control element. Taking the design of a benzene storage tank as an example, this tank employs a \"2-out-of-2\" logical structure; level measurement is carried out using one process-level radar level gauge and one metering-level radar level gauge. Interlock conditions are established with high-high and low-low level switches, and through calculations performed by a Logic Solver, it is possible to activate the emergency shut-off valves at the inlet and outlet for safety interlocks. Installing emergency shut-off valves that meet the requirements, in accordance with industry standards and production practices, and continuously improving the safety interlock protection system are of great significance for ensuring the safe operation of production facilities and protecting the lives and property of personnel. Design entities should handle tasks such as the selection of emergency shut-off valves and the design of safety interlock protections. Meanwhile, operating entities should continuously explore and make improvements during the production process to render their application more rational and standardized; this will undoubtedly enable them to fully exert their positive role in safety protection.