【Haichuan Chemical Valve Management】Rationale for installing dual valves on pipelines for series of discharge ports (discharge outlets, condensate discharge ports, sampling ports, etc.)

Thread Content

Proper management of valves is the foundation for stable operation. Everyone is welcome to engage in discussions and share insights on this series of posts: 【HaiChuan Chemical Valve Management】 series of posts: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=5719309 ---------------------------------------------------------------- Disclaimer: The content contained in this article is intended solely for technical exchange and reference purposes only; it does not constitute any form of professional engineering advice, design basis, or operational guidance. ----------------------------------------------------------------------------------- There are several criteria for specifying dual-valve systems: 1. Article 5.3.7 of the \"Design Code for Tank Areas in Petrochemical Storage and Transportation Systems\" SH/T 3007-2014: A main isolation valve should be installed near the tank base on the inlet and outlet pipes for the tank’s contents, and an operating valve should also be installed on each of these pipes. The drain pipe of the storage tank should be equipped with double valves. Section 6.4.4: Anti-freezing measures shall be taken for the bottom piping of liquefied hydrocarbon storage tanks in cold regions. A double valve should be installed on the dehydration pipeline of the liquefied hydrocarbon tank. 2. Article 7.1.4.2 of the \"Design Code for Occupational Safety and Health in Petrochemical Enterprises\" SH/T 3047-2021: Reliable sealing measures shall be adopted at those parts of equipment, pumps, pipelines, fittings, etc. where material leakage is likely to occur. At the discharge outlets and sampling ports of equipment and pipelines, measures such as the installation of blind flanges or double valves should be adopted. Clause 7.1.5.6: Discharge valves for highly corrosive liquids should be equipped with double valves. 3. Article 8.1.7 of the \"Code for Design of Layout of Metal Piping in Petrochemical Industries\" SH/T 3012-2011: For piping carrying extremely hazardous media, dual valves shall be installed for venting or draining, and the flow shall be directed into a closed recovery system. Article 8.1.10: Double valves shall be provided for the venting or draining of high-pressure pipelines; when a single valve is used, a blind flange and a flange cover shall be installed. Article 8.1.11: For the drainage at the lowest point of combustible gas pipelines that are in continuous operation, a double valve should be installed, and the liquid discharged should be sent to a closed system ； Combustible gas pipelines should be drained only during startup and shutdown; a valve can be installed, along with a plug, pipe cap, or flange cover. When a shut-off valve is installed for draining on combustible liquid and steam pipelines, a plug, pipe cap, or flange cover should be added at the end. Article 9.4.1: When semi-fixed purging nitrogen is required in the installation, a nitrogen connector shall be provided at the hose station, along with a double valve. 4. Article 6.0.7 of the \"Design Code for Instrument Piping and Wiring\" HG/T 20512-2014: When the pressure class is greater than or equal to PN160 and the root valve is a double-valve type, the instrument drain valve should be designed as a double valve or as a single valve accompanied by a pipe cap. 5. Article 10.2.4 of the \"Code for Environmental Protection Design in Petrochemical Industries\" SH/T 3024-2017: For pipelines carrying highly hazardous media, dual valves shall be used for discharge, and the flow shall be directed into a closed recovery system ； The discharge of other toxic media can use a single valve with a flange cover. For the discharge of high-pressure fluid medium pipelines, a dual-valve system or a single valve with a flange cover should be used; for the discharge of other fluid medium pipelines, a single valve with a flange cover should be employed. Article 10.2.10: Centrifugal pumps or rotary pumps used for transporting process materials should be equipped with mechanical seals. For centrifugal pumps and rotary pumps used to transport toxic media, sealless pumps should be employed, and the sealing grade should be increased. Centrifugal pumps or rotary pumps used to transport toxic and hazardous media should be equipped with bottom drain valves, which should be designed as a dual-valve system. 6. Article 7.2.7 of the \"Code for Fire Protection Design of Petrochemical Enterprises\" GB 50160-2008 (2018 edition): When utility pipelines are connected to pipelines or equipment carrying flammable gases, liquefied hydrocarbons, and flammable liquids, the following requirements shall be met: 1. Check valves shall be installed on utility pipelines that are in continuous use, with isolation valves placed at their bases ； 2. Check valves and one isolation valve, or two isolation valves, shall be installed on utility pipes that are used intermittently, with a service valve installed between the two isolation valves ； Article 7.2.8: Two drain valves shall be installed at the lowest point of combustible gas pipelines that are in continuous operation, and the liquid drained shall be discharged into a closed system ； For drain valves used only during startup and shutdown, a single valve can be installed along with a plug, pipe cap, blind flange, or flange cover. 7. Article 5 of the \"Guiding Opinions of the State Administration of Work Safety on Strengthening Leak Management in Chemical Enterprises\" (An Jian Zong Guan San [2014] No. 94): When designing discharge valves such as those at the outlets and sampling points of equipment and pipelines, measures such as the use of blind flanges, plug valves, pipe caps, and double valves should be employed to reduce the likelihood of leaks. For processes involving highly toxic or extremely toxic substances, a closed sampling system should be used; for the safe venting of toxic and flammable gases, closed-system designs must be adopted. 8. Clause 2.0.3.1 of the “Technical Specifications for the Design of Process System Engineering” HGT 20570-1995: For storage tanks holding liquefied petroleum gas, other flammable, toxic, valuable liquids, highly corrosive substances (such as concentrated acids and caustic soda), and materials with special requirements (such as those that emit foul odors and cause severe environmental pollution), two valves in series should be installed on the pipes leading from the bottom of the tank to other equipment. Regardless of whether there are valves near those other devices, one of these valves should be positioned right next to the tank’s connection port; when the tank has a large capacity or is located at a considerable distance, it is preferable that this valve be a remotely controlled one. Clause 2.0.3.2: When it is necessary to shut down the equipment for maintenance, cleaning, or regeneration during operation of the unit, double valves should be installed, with a check valve placed between them. When the device is disconnected from the system, both valves close and the check valve opens. Clause 2.0.3.5: For materials such as hydrocarbons and toxic or hazardous chemicals, at the connections to other process materials, as well as on the vent and drain pipes, dual valves should be installed; refer to Table 2.0.3 for details. 9. \"Code for Design of Spherical Storage Tanks for Liquefied Hydrocarbons in Petrochemical Industries\" SH 3136-2003, 6.3 Drain Valves: Two cut-off valves should be installed on the drain pipes of spherical storage tanks for liquefied petroleum gases, and a direct drainage method is preferred. 10. \"Code for Design of Flammable Gas Emission Systems in Petrochemical Industries\" SH 3009-2013 5.5.5: Subject to the requirement of safe emission of flammable gases, switching operations can be carried out between multiple flares ； The transition piping between torches should be installed in front of the water seal tank, and double isolation valves as well as blind flanges should be provided.