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Key words: pipeline engineering; valve; leakage; quality defect; installation and construction; preventive measures Valve is the control component of oil and gas pipeline, its function is to change the pipeline section and the transport direction of oil and gas medium, with diversion, cutoff, throttling, non-return , split or overflow, pressure relief and other functions.
1 Analysis of valve leakage The valve leakage is generally divided into external leakage and internal leakage. The internal leakage refers to the valve closing is not strict due to the erosion wear of the conveying medium, the sealing surface scratching, etc., and the transportation cannot be completely prevented after the valve is completely closed. External leakage generally refers to the defect of the valve body itself, the tight connection between the flange connection surface or the connecting thread, which causes the conveying medium to flow out or leak out of the valve body.
1.1 Analysis of the causes of leakage of the valve (1) The quality defects caused by the valve during the production process. The first is the leakage caused by the quality defects formed by the casting valve during the casting process. It includes defects such as sand holes, sand inclusions, slag holes and pores formed in the casting body. When the surface metal and paint coating of the defect surface are corroded and impacted, the hole gradually expands and leaks. The second is the leakage caused by the quality defects formed by the forging valve during the forging process. Such as cracks, cracks, folding and other issues. These inherent defects can cause leakage under the pressure of the conveying medium.
(2) Leakage caused by improper installation of the valve flange. First, when the pipeline engineering valve is installed, the number of buckles tightened by the tightening nut is inconsistent, uneven or the gasket is selected incorrectly, so that the seal is too thin and the tightness after pressing is not enough to seal. The medium leaks to the outside of the valve body under pressure. Second, the pipe support system sinks, the position or the support system is improperly adjusted, and the pipe flange section is not parallel or misaligned with the valve flange section. There is stress between the pipe flange and the valve flange during installation, resulting in a gasket. It cannot be completely compacted and filled, causing the transport medium to leak to the outside of the valve body. Third, when the valve flange is installed, it is not tightened to the standard specified torque value, the flange sealing surface is scratched, the radial groove or other defects, the bolt sliding wire, etc. cause the individual bolts to loosen and the flange sealing surface is partially loosened. The conveying medium leaks to the outside of the valve body under the action of pressure.
(3) Leakage caused by the filler. Some pipeline engineering valves are used to prevent leakage of gas, liquid materials and other media, and the sealing device of the valve stem portion is provided as a packing. When the packing is installed, the gland is tightly biased, the packing bolts are not fastened, the packing is too small, the packing selection is incorrect, and the packing installation method is not correct.
1.2 Analysis of the cause of leakage inside the valve (1) The leaking part of the valve. Under normal circumstances, the internal leakage of the valve often occurs in three parts: one is the internal leakage of the contact between the opening and closing parts and the sealing surface of the valve seat; the second is the internal leakage of the connection between the valve body and the valve cover; the third is the adjustment of the valve closing position. In place, an internal leak occurs.
(2) Analysis of the cause. First, the valve design unit is not properly designed. The valve design is not properly selected. The oil and gas pipeline transport medium, the temperature of the transport medium and the ambient temperature, flow rate, pressure and other factors are not considered comprehensively. The selected valve pressure level and structural form do not meet the actual conditions of the medium transported in the oil and gas pipeline, resulting in the valve being A leak occurred during use. Second, the valve manufacturer failed to produce. The purchased sealing ring does not meet the requirements of design selection. The material technical specifications do not meet the requirements of the technical specification; the sealing ring is not installed properly or the defective sealing ring is used, but the valve pressure test is not found, resulting in leakage of the valve in the pipeline. Valve and bonnet processing dimensions are too poor, the assembly is not in place; the valve switch position is not adjusted, so that the valve can not close the valve when all the closing indicators are closed, causing the valve to leak; the valve is not adjusted to the factory when it is shipped to the factory. Fully open position, or no protection at both ends of the valve, causing impurities to enter the valve cavity. Third, the supervision of the supervision unit in the valve production process is weak. The supervisory unit did not play its due role in quality supervision, so that the valve that had produced the internal leakage defect was shipped. Fourth, the valve transport unit does not operate according to the specifications. During the transportation process, the valve is not handled according to the loading and unloading and transportation regulations. The valve binding, fixing and protection are unreasonable, causing internal or internal damage to the valve due to bumps and vibrations during the loading and unloading process. Fifth, the valve transit logistics unit (transfer station) is improperly kept. After the valve is received, it is savagely loaded and unloaded during the lifting process. During the storage process, the correct stacking valve or valve is not stored in the transfer station for too long. The correct maintenance is not implemented, resulting in the lubricating oil in the valve. Aging deterioration and aging of the sealing surface, etc., which will lead to leakage inside the valve. Sixth, the valve installation and construction unit did not handle it properly. The valve installation and construction unit improperly store the valve received; when the valve is pressure tested on the pipeline, there are too many impurities inside the pipeline, and the cleanliness of the water is not up to standard, resulting in damage to the sealing surface of the valve, causing damage to the valve and causing leakage inside the valve. Seventh, the valve construction supervision unit is not strict. In the process of valve installation, commissioning, pipeline purging and pressure testing, the quality assurance system fails, resulting in damage to the valve or leakage inside the valve. Eighth, the valve user and the owner unit do not follow the valve operation rules. The routine maintenance process does not check, maintain, lubricate and replace the packing gasket regularly according to the regulations, causing the valve stem to rust, the switch not open, or even jamming. Phenomenon; can also cause the aging of fillers and gaskets, aging and deterioration of lubricating oil (fat) are the causes of leakage inside the valve.
2 Measures to prevent valve leakage (1) The valve design unit should be considered. When selecting the valve, the valve design unit should have a detailed understanding of the internal structure of various types of valves and the medium, temperature, flow rate, flow rate, temperature limit of the station, etc., combined with process, operation and safety factors. Select the valve with reasonable pressure level and structural form, caliber and material to meet the requirements of use and easy on-site maintenance, including the following four aspects.
1) Working pressure, working temperature, ambient temperature, corrosiveness of oil and gas pipeline transportation medium, whether it contains solid particles, whether it is toxic, whether it is flammable or explosive.
2) The requirements of the valve on the medium characteristics of the oil and gas pipeline transportation, such as flow resistance, discharge capacity, flow characteristics, sealing level, etc.
3) Oil and gas pipeline requirements for valve installation size and external dimensions, such as nominal diameter, connection with piping, installation size, external dimensions or weight restrictions.
4) Additional requirements for the reliability of the valve product, the maintenance of the service life and the explosion-proof performance of the electric device.
3 Conclusion In summary, there are many reasons for valve leakage. This requires valve manufacturers, construction companies and related departments to take various measures to prevent, minimize, or minimize the production, design, procurement, supervision, inspection and storage, installation and use. Avoid leakage.
References [1] He Xinjian, Li Baoping, Li Danli, Shen Weidong. Reasons and Countermeasures for Urban Underground Gas Pipeline and Valve Well Leakage[J].Fire Science and Technology,2000,04:48-49+3.
[2]Liu Yinglai. Failure Analysis and Treatment of Three-way Leakage in Pipeline Engineering [A]. China Mechanical Engineering Society, Hunan Provincial People's Government. Proceedings of the Annual Meeting of China Mechanical Engineering Society in 2007 [C]. China Mechanical Engineering Society, Hunan Provincial People's Government: 2007:1.
Causes and Countermeasures for Leakage of Pipeline Engineering Valves
Abstract: Valve leakage occurs during the construction of pipeline engineering, which will result in the failure of pipeline engineering to be delivered on time. Oil and gas leakage during the commissioning or commissioning of the project will not only cause waste of oil and gas resources, but also cause damage to the surrounding environment of the pipeline project. It even caused serious safety incidents. Therefore, it is necessary to analyze the causes of leakage of oil and gas pipeline engineering Valves and take effective measures to prevent and eliminate valve leakage.