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Abstract: From the perspective of safety auditing. 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. The reason for this is mainly that the LPG pipelines did not fully comply with the requirements of relevant industry regulations, technical specifications, or standards in terms of design, installation, supervision and inspection, as well as operation and maintenance; as a result, quality issues or safety hazards arose, which ultimately led to the accident. 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 focused on the safe operation of liquefied petroleum gas gasification stations, with an emphasis on liquefied petroleum gas pipelines; I found that there are still some quality issues in the construction of these 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 is based on the operating conditions to determine the design pressure and design temperature; these are the most fundamental requirements for pipeline design. They influence the selection of materials for the pipes, as well as for pipe fittings and valves, and also affect 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 mismatch between the operating conditions of the pipeline and 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 LPG storage and distribution stations, the tank transfer procedure in case of an accident is taken into account ； Hydrocarbon pumps and compressors are 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 is installed at the pump inlet to prevent impurities from entering the pump and damaging it ； A gas-liquid separator is installed at the inlet of the hydrocarbon compressor to prevent liquid from entering the compressor cylinders and causing cylinder explosion accidents ； A safety valve is 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, are also taken into consideration. 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 degassing in the 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 corresponding pipe fittings (such as flanges, threaded splices, elbows, tees, unions, etc.) are 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. Installations are inspected and accepted 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, are equipped with measures for lightning protection and static electricity prevention. 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 LPG pipeline installation team possesses 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 meet the requirements for on-site welding. Generally, welders are required to have skills in fixed welding for pipes, vertical fixed welding, and pipe sheet welding in order to meet the requirements for all welding tasks. 2.3 Installation plan The installation plan includes organizational methods and technical methods, among which the technical methods are the most important. Whether the technical approach is complete and comprehensive, and whether it is 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 specifications 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, as well 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. Inspection and supervision 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 inspection and supervision ； Secondly, it is necessary to check whether the installation plan for Foot Review Night is correct and complete, and whether it can ensure the quality of the installation ； Once again, verify whether the records of women’s clothing are complete, accurately reflect the actual construction progress, and whether the women’s clothing plan was 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. Mainly involve 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 appearance 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 tests. 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 is 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. (3) Process flow inspection. The main checks involve verifying whether the process parameters such as the connections of liquefied petroleum gas pipelines, the flow direction of the medium, the installation locations of measuring instruments, and the installation locations of control devices meet the requirements specified in the design drawings. (4) Installation quality inspection. It mainly involves checking dimensional errors such as the proper levelness and alignment of pipe installations, as well as assessing the quality of bracket and hanger installations, the anti-corrosion treatment of buried pipes, and lightning and static electricity protection facilities. (5) Overall inspection. Primarily, strength tests and airtightness tests are used to check whether the overall installation quality of the pipeline meets the requirements for design and operation. It should be noted that the requirements regarding the number of pressure gauges used, their range, accuracy, installation location, testing time, and inspection methods must not be lower than those specified in GB50235—97 \"Code for Construction and Acceptance of Industrial Metal Piping Projects\". In particular, a high-precision pressure gauge with fine scales should be used for the 24-hour airtightness test. It is necessary to carefully record the values of pressure and temperature changes in order to accurately calculate the leakage rate. In short, with the development of industry, liquefied petroleum gas pipelines are being used more and more widely in industrial production and people’s daily lives. However, due to the flammable and explosive nature of liquefied petroleum gas, it is necessary to take careful attention to aspects such as design, installation, supervision, and inspection, to consider all relevant factors and avoid any negligence or omissions. This ensures the quality of construction of liquefied petroleum gas pipelines and provides a guarantee for their safe use.