Some problems needing attention in the constructio

Several problems that should be paid attention to in the construction of liquefied petroleum gas pipelines

in recent years, domestic liquefied petroleum gas pipeline leakage, fire or explosion accidents have occurred frequently, causing serious harm to the safety of people's lives and property. The main reason is that the LPG pipeline has not fully implemented the requirements of relevant national or industrial regulations, technical specifications or technical standards in terms of design, installation, supervision and inspection, use and maintenance, and there are quality problems or potential safety hazards, which eventually leads to accidents. I have been engaged in the safety supervision of boilers, pressure vessels and pressure pipelines for many years. I have conducted many safety supervision and inspections on more than 20 LPG storage and distribution stations and more than 200 gasification stations (bottle group gasification station and tank gasification station) in the city, and participated in the safety use investigation of LPG gasification stations (mainly for LPG pipelines) in the city. I found that there are still some quality problems in the construction of LPG pipelines, It always threatens the safe use. Next, several points for attention in the construction of LPG pipelines in storage and distribution stations and gasification stations are put forward for reference in the design, installation, supervision and other aspects of liquid fossil oil and gas

1 in terms of drawing design

1.1 design parameters

the design pressure and design temperature of LPG pipeline must be determined according to the service conditions. This is the most basic requirement of pipeline design, and it is related to the design, selection, installation and inspection of pipes, pipe fittings, valves and other materials. Common problems in design include: the design pressure and design temperature of the pipeline are not indicated in the design drawings, or the design pressure and design temperature are improperly selected, which directly affect the final quality and service conditions of the pipeline. For example, the liquefied petroleum gas storage and distribution station has formulated the detailed outline of the field survey of China Mongolia joint long tune folk songs. The design parameters of the pipeline directly connected to the tank inlet and outlet (without decompression) should be the same as the tank design parameters, that is, the design pressure is 1.8MPa, not 1.6Mpa, and the design temperature is 60 ℃; Otherwise, there will be the problem that the service conditions of the pipeline and the storage tank are not matched

1.2 safety of process flow

this requires that the pipeline design must start from the overall design and consider the safe use requirements of the whole process system. For example, the pipeline design of LPG storage and distribution station must consider the tank pouring process in case of accidents; Hydrocarbon pumps and compressors must be equipped with bypass pipelines; Vent valve shall be set at the outlet of hydrocarbon pump to prevent the pump from pumping out, and check valve shall be set to prevent the backflow of outlet liquid from damaging the hydrocarbon pump when the pump suddenly stops during operation; The pump inlet must be equipped with a filter to prevent impurities from entering the pump and damaging the hydrocarbon pump; A gas-liquid separator must be set at the inlet of the hydrocarbon compressor to prevent cylinder explosion caused by liquid entering the compressor cylinder; The pipeline between the two stop valves must be equipped with a safety valve to prevent the pipeline from bursting due to the rising sun temperature and pressure of the pipeline; It is also necessary to consider the safety issues such as thermal expansion and cold contraction of pipelines (especially the unloading pipelines at the wharf, with large operating temperature difference), and the operating vibration of hydrocarbon pumps and compressors. For example, a liquefied petroleum gas unloading dock in Shekou City, due to the unreasonable setting of the fixed support of the liquid phase pipeline, more than 200 meters long pipeline cannot expand or contract freely when heated or cooled. When unloading gas in summer, sometimes the temperature of the liquid phase LPG discharged from the ship is only a few degrees above zero, which is 20 or 30 degrees different from the normal temperature of the pipeline, resulting in a large general PE elongation of 90% - 950% (among which the elongation of linear low density polyethylene LLDPE is high) temperature difference stress. For a long time, this has caused obvious deformation of the connecting flange on the pipeline

1.3 selection of pipes and accessories

the pipes used for liquid-phase LPG pipelines and gas-phase LPG pipelines with a design pressure of more than 0.6MPa should be high-quality seamless steel pipes, rather than seamless steel pipes; The supporting pipe fittings (such as flanges, threaded nipples, elbows, reducer, tees, etc.) must be made of high-quality carbon steel (seamless), rather than cast iron. For gas-phase liquefied petroleum gas pipelines with a design pressure lower than o.6mpa, the requirements can be reduced accordingly in accordance with the code for design of urban gas (gb50028-93). For example, in 1995, a 13m3 buried liquefied petroleum gas storage tank in a printing and dyeing factory in Shekou, our city, with a design pressure of 1.76Mpa, and the liquid and gas phase inlet and outlet pipes of the storage tank are connected to the pipeline with cast iron threaded nipples; Due to the unreasonable setting of the support of the liquid inlet pipe, there was a large vibration. Under the long-term vibration, the connecting cast iron threaded nipple was broken, resulting in a large number of LPG leakage. Fortunately, the treatment was timely, which did not cause a fire or explosion accident

1.4 selection of installation and acceptance specifications

the installation and acceptance specifications used in the design of liquefied petroleum gas pipelines cannot be lower than the national standard gb50235-97 industrial metal plumbers: Code for construction and acceptance of engineering. If multiple installation and acceptance specifications are used on the design drawings, when the specifications conflict with each other. The principle of "high is not low" should be adopted. Adopt higher specifications for installation acceptance

1.5 lightning protection and anti-static facilities

liquid fossil A. test standard modular function: provide users with the test oil and gas pipelines that need to be used for setting, and the equipment or facilities connected with them must be equipped with lightning protection and anti-static measures. To prevent accidents caused by lightning strike or static electricity caused by medium flow and friction in the pipeline