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1. Condensate: Gas often contains water vapor, and a decrease in temperature or an increase in pressure causes this water vapor to condense into water, which then flows to the lowest points of the pipes or condensate tanks. If this amount of condensate isn’t removed in time, it can cause blockages in the pipes. Solution: To prevent water accumulation from blocking the pipes, strict operating procedures must be established to regularly drain the condensed water from the condensate tanks. For each water collection tank, location cards and pumping records should be kept, documenting the date of pumping and the amount of water pumped, which serve as important references for determining the pumping schedule. It also allows for the early detection of abnormalities such as groundwater intrusion. 2 Infiltration When the pressure of groundwater is higher than that of the gas inside the pipeline, it may seep into the pipeline through poorly sealed joints, corrosion holes, or cracks. It generally occurs in areas where pipes are old and in poor condition, where the pipes are corroded or damaged, or where the joints become loose due to construction defects, or when the pipe burial depth does not meet the specified requirements, under the influence of surface dynamic loads. And the location where the pipeline came loose or broke. Solution: When the water level in the condensate tank increases sharply, it may be caused by leaks. In such cases, the relevant section of the gas pipeline can be closed, and gas at a pressure higher than that of the leakage can be pumped in. Then, the location of the leak can be identified using leak detection methods, and repairs can be carried out to restore normal gas supply. 3. Naphthalene: Artificial gas often contains a certain amount of naphthalene vapor, which condenses into a solid when the temperature drops. Alternatively, if the equipment used to remove naphthalene is not adequate, it can accumulate on the inner walls of the pipes, reducing the flow of gas or even completely blocking the pipes. In cold seasons, naphthalene tends to accumulate in the curved parts of the pipes or at the junctions where underground pipes meet the surface pipes. Solution: To prevent and eliminate naphthalene, it is necessary to strictly control the content of naphthalene in the gas released from factories in accordance with relevant standards; this will allow the problem of naphthalene accumulation in pipelines to be resolved at its root. Furthermore, in urban gas pipelines, especially those within 1 to 2 kilometers of the plant, a large amount of naphthalene often accumulates on the inner walls, so regular cleaning is necessary. A spray valve can be used to inject heated diesel, volatile oils, or a mixture of diphenyls into the pipe, allowing the naphthalene to dissolve and then flow into the condensate tank, from where it is discharged along with the condensate. Since it can be dissolved by warm water at 70 ℃, the two ends of the pipeline section can also be segmented, and hot water or steam can be introduced to remove naphthalene. However, this method causes the pipes to expand and contract with temperature changes, which can easily lead to loosening of the flexible joints; therefore, after cleaning the gas pipes using this method, a gas-tightness test should be conducted. In low-pressure pipelines, the areas where naphthalene accumulation is severe are usually found in the branch pipes leading into the building. These can be cleaned by using wire attached to steel rods, or by digging out the section of pipe underground that is blocked and then using a vacuum pump to remove the naphthalene. 4 Other impurities In addition to naphthalene accumulation, the buildup of other impurities within the pipes can also cause blockages. The main component of these impurities is rust particles, which often accumulate in the pipes along with tar dust and other substances. Steel pipes without an inner wall coating or with poorly applied coatings suffer from much more severe corrosion than cast iron pipes, producing mainly rust flakes. The method for removing impurities is to mechanically clean the main pipes in sections; generally, a section of about 50 meters is cleaned at a time. As for iron shavings, these can be removed from inside the broken pipes by using scrapers and wire brushes to clean the inner walls of the pipes. Sometimes, when too much rust debris adheres firmly to the pipe walls, it is difficult to remove. When cleaning the rust, attention should also be paid to any corrosion pits on the pipe walls, so as to avoid puncturing the pipe and causing air leakage. If the bends in the pipes, valves, and drains are blocked, they can be removed for cleaning or replaced. 5 Pipe slope The slope of gas transmission pipes is steeper than that of water pipelines, resulting in more frequent blockages; therefore, a proper slope helps to remove accumulated liquid and impurities, so the pipe slope must be greater than 5‰. 6 Operation and Management The continuous drainage from the water seals along the gas pipeline, proper cleaning of the pipeline, the efficiency of the tar removal devices, as well as the performance of the naphthalene removal equipment are all aspects that cannot be ignored. In summary, to reduce blockages in coal gas pipelines, it is necessary to improve the quality of the clean coal gas, enhance equipment operation, and strive to increase the efficiency of desulfurization and decyanidation. Strive to increase the operation rate and collection efficiency of the electrostatic tar remover, control the operating temperature of naphthalene properly, and minimize the tar content in the gas. Strengthen construction management and clean the gas pipelines 1 to 2 times per year. If all the above measures are consistently implemented, the urban gas transmission and distribution pipelines can operate safely and normally.