【Common Issues in Haichuan Pipeline Design】Incorrect connection method for flammable liquid pipelines

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Incorrect connection method for pipelines carrying flammable liquids. GB 50160-2008 \"Code for Fire Protection Design of Petrochemical Enterprises (2018 Edition)\", 7.2.1: Metal pipelines for flammable gases, liquefied hydrocarbons, and flammable liquids shall be connected by welding, in addition to being connected using flanges. For metal pipes and valves of flammable gases, liquefied hydrocarbons, and flammable liquids with a nominal diameter equal to or less than 25 mm that are connected using tapered pipe threads, seal welding shall be applied at the threads, except for pipes carrying media prone to crevice corrosion. Explanation of the provision 7.2.1 This provision specifies that flange connections should be used in the following situations: (1) connections to the nozzles of equipment, connections to flanged valves, etc ； (2) Pipes prone to blockage, such as high-viscosity, sticky polymer slurries and suspensions ； (3) Pipelines for liquids with high freezing points such as paraffin, asphalt, sulfur, etc ； (4) Pipelines and other components that need to be removed for shutdown maintenance. Pipelines are connected by welding, which provides good strength and sealing performance. However, for pipes equal to or smaller than DN25, the welding strength is poor and slag tends to fall into the pipe causing blockages; therefore, socket weld fittings are commonly used, as well as tapered pipe threads. When tapered pipe threads are used, in the presence of highly corrosive media, especially those prone to crevice corrosion such as those containing HF, sealing welds must not be applied at the threaded connections; otherwise, leaks can lead to serious consequences.