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Summary of several issues to be noted in LPG pipeline construction: from the perspective of safety supervision. Regarding the design of process pipelines in liquefaction plants. Issues that require attention are raised. In recent years, leaks, fires, and explosions in domestic liquefied petroleum gas pipelines have occurred frequently, causing serious harm to people’s lives and property. Analyzing the reasons, it is mainly due to the fact that in terms of design, installation, supervision and inspection, as well as use and maintenance, liquefied petroleum gas pipelines have not fully complied with the requirements of relevant industry regulations, technical specifications, or standards; as a result, quality issues or safety hazards exist, which ultimately lead to accidents. I have been engaged in the supervision of safety related to boilers, pressure vessels, and pressure pipelines for many years. I have conducted numerous safety inspections at over 20 liquefied petroleum gas storage and distribution stations as well as more than 200 gasification stations (both bottle-group gasification stations and tank-based gasification stations) in this city. I have also taken part in research efforts aimed at ensuring the safe use of liquefied petroleum gas gasification stations, with a focus on liquefied petroleum gas pipelines; these efforts revealed that there are still some quality issues in the construction of such pipelines, which pose a constant threat to their safe use. The following outlines several points to consider regarding the construction of liquefied petroleum gas pipelines at storage and distribution stations as well as gasification stations, to serve as a reference for the design, installation, and supervision of liquefied petroleum gas systems. 1. Drawing design 1.1 Design parameters: The design of liquefied petroleum gas pipelines requires that their design pressure and design temperature be determined based on the operating conditions. This is the most fundamental requirement for pipeline design; it influences the selection of materials for the pipes, as well as for pipe fittings and valves, and it also affects subsequent steps such as installation and inspection. Common problems in design include: the design drawings not specifying the design pressure and design temperature of the pipes, or inappropriate selection of these values, all of which directly affect the ultimate quality and operating conditions of the pipes. For liquefied petroleum gas storage and distribution stations, as well as pipelines that are directly connected to the inlet and outlet of the storage tanks without pressure reduction, the design parameters should be the same as those of the storage tanks themselves; that is, the design pressure is 1.8 Mpa rather than 1.6 Mpa, and the design temperature is 60℃ ； Otherwise, there will be a problem of the pipeline not matching the operating conditions of the storage tank. 1.2 Safety of the process flow: This requires that pipeline design be approached from an overall perspective, taking into account the safety requirements of the entire process system. For example, in the pipeline design of liquefied petroleum gas storage and distribution stations, the tank transfer process in the event of an accident must be taken into account ； Hydrocarbon pumps and compressors must be equipped with bypass pipelines ； A vent valve should be installed at the outlet of the hydrocarbon pump to prevent the pump from running dry, and a check valve should be placed there to prevent the liquid at the outlet from flowing back and damaging the hydrocarbon pump in case of an unexpected stoppage of the pump ； A filter must be installed at the pump inlet to prevent contaminants from entering the pump and damaging it ； A gas-liquid separator must be installed at the inlet of the hydrocarbon compressor to prevent liquid from entering the compressor cylinders and causing cylinder explosion ； A safety valve must be installed in the pipeline between the two shut-off valves to prevent the pipeline from bursting due to increased temperature and pressure caused by exposure to sunlight ； Safety issues such as thermal expansion and contraction of pipelines (especially those used for unloading ships at docks, where temperature differences during operation are significant), as well as vibration during the operation of hydrocarbon pumps and compressors, must also be taken into account. For example, at a liquefied petroleum gas unloading terminal in Shekou of our city, improper installation of the fixing brackets for the liquid-phase pipelines prevented pipes over 200 meters long from expanding or contracting freely when heated or cooled. During decompression in summer, the temperature of the liquid-phase liquefied oil and gas unloaded from the ship is sometimes only a few degrees above zero, which is twenty to thirty degrees different from the normal temperature of the pipeline; this creates significant thermal stress. Over time, this leads to noticeable deformation of the connection flanges on that pipeline. 1.3 Selection of pipes and fittings: For liquid liquefied petroleum gas pipelines and gas-phase liquefied petroleum gas pipelines with a design pressure of 0.6 Mpa or higher, high-quality seamless steel pipes should be used, rather than welded steel pipes ； The materials for the associated pipe fittings (such as flanges, threaded splices, elbows, tees, unions, etc.) must be high-quality carbon steel (seamless); cast iron materials cannot be used. For gas-phase liquefied petroleum gas pipelines with a design pressure of less than 0.6 Mpa, the requirements can be appropriately reduced in accordance with the provisions of the \"Code for Design of Urban Gas Systems\" (GB50028—93). For example, in 1995, at a printing and dyeing factory in Shekou of our city, there was a 13M3 underground liquefied petroleum gas storage tank with a design pressure of 1.76 Mpa; the inlet and outlet pipes for the liquid and gas phases of this tank were connected to the pipeline using cast iron threaded fittings ； Due to the improper installation of the supports for the liquid inlet pipes, significant vibrations occurred. Over time, these vibrations caused the cast iron threaded joints to break, resulting in a large amount of liquefied petroleum gas leakage. Fortunately, prompt action was taken, which prevented any fires or explosions from occurring. 1.4 Selection of installation and acceptance specifications: The installation and acceptance specifications chosen for the design of liquefied petroleum gas pipelines must not be lower than the standard GB50235—97 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\". If multiple installation and acceptance specifications are specified in the design drawings, and those specifications conflict with each other, then… The principle of \"taking the higher value rather than the lower one\" should be applied. Installation acceptance is carried out in accordance with higher-standard specifications. 1.5 Lightning and static electricity protection facilities: Liquefied petroleum gas pipelines, as well as the equipment or facilities connected to them, must be equipped with measures for protecting against lightning and static electricity. To prevent accidents caused by lightning strikes or static electricity generated by friction from the flow of the medium inside the pipes. 2 Installation aspects 2.1 Qualifications of the installation team The pipeline installation team for liquefied petroleum gas must possess installation qualifications at the appropriate level. 2.2 Qualifications of welders: Welders must hold a qualification certificate for welding boilers and pressure vessels. Its qualified test items (welding position, steel grade, welding orientation, allowable diameter and wall thickness, etc.) and validity period must meet the requirements of on-site welding. Generally, welders are required to have certification in fixed welding for pipes and ducts, vertical fixed welding, and tube sheet welding in order to meet the requirements for all welding tasks. 2.3 Installation plan The installation plan includes organizational measures and technical measures, among which the technical measures are the most important. Whether the technical measures are complete and comprehensive, and whether they are correct. It is directly related to the installation quality and serves as the fundamental guarantee for it. The installation plan mainly includes technical requirements such as the basis for preparation, the installation and acceptance standards adopted, the inspection or testing of raw materials (pipes and fittings, valves, etc.), welding procedures, requirements for self-inspection during installation, hydrostatic testing, airtightness testing, 24-hour leakage rate testing, and inspection of lightning and static electricity protection facilities. In particular, the quality of pipe installation must meet the requirements of standard GB50235—97 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\", while the quality of pipe welding must meet the requirements of standard GB50236—97 \"Code for Construction and Acceptance of Welding of Field Equipment and Industrial Metal Piping\". 2.4 Installation Records The installation records reflect the circumstances of the pipeline installation process; they are an important part of the completion documents for pipeline installation, and also serve as a crucial basis for quality supervision and inspection during installation. The installation records should include: records of drawing reviews, construction technical documents, raw material inspections, welding, concealment of buried pipes, strength and airtightness tests, as well as inspections of lightning and static electricity protection facilities. 3. Supervision and inspection 3.1 Document review First, it is necessary to examine whether the design drawings meet the requirements of relevant laws, regulations, standards, and specifications, and to determine the key points for supervision and inspection ； Secondly, it is necessary to check whether the installation plan for Foot Exam Night is correct and complete, and whether it can ensure the quality of the installation ； Once again, check whether the records of women’s clothing are complete, accurately reflect the actual construction progress, and whether the women’s clothing plan has been followed: by examining the construction records, it is possible to trace the quality of the women’s clothing. And more importantly, it enables the timely detection of problems during installation. 3.2 Quality Inspection (1) Raw material inspection. It mainly involves checking the material quality certificates to confirm whether the material quality meets the requirements ； Check the inspection or testing records of the raw materials. Verify whether sufficient raw materials are available for pre-installation inspection or testing in accordance with relevant regulations or design requirements. Such as random inspections of the visual quality and dimensions of pipes, as well as tests or inspections of valves using pressure testing and leak testing. (2) Welding quality inspection. 1. Verify whether the welder’s qualifications meet the requirements for welding work, and whether welding is carried out according to the tasks for which they have passed the relevant examinations. 2. Randomly inspect the weld quality. First, the visual quality of the weld is inspected, focusing mainly on the surface dimensions of the weld and any surface defects ； Next is to inspect the internal quality of the weld. ·Radiographic testing or ultrasonic testing methods are generally used. In the random inspection of weld quality, samples should be taken proportionally from various types of welds welded by different welders, such as fixed weld joints and rotating weld joints, butt weld joints with different wall thicknesses, and butt weld joints of different pipe fittings, to ensure that the sampled welds are representative. This allows for a more comprehensive assessment of the overall welding quality.