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The main purpose of cleaning natural gas pipelines is to remove water from them. Since natural gas generally contains acidic gases such as H2S and CO2, hydrates are likely to form, causing pipeline blockages. To remove water from the pipeline, a straight-bar cleaner with good sealing properties should be used. The difference between cleaning natural gas pipelines and oil pipelines is that in the case of long-distance, large-diameter gas pipelines, the operating pressure is generally around 10 MPa, the gas flow velocity can reach about 10 m/s; moreover, due to the high compressibility of natural gas, the range of variations in gas flow velocity is relatively large. However, research has shown that the more stable the velocity of the pig in the pipeline, the better the cleaning effect; if the velocity is too high, it will affect the cleaning efficiency. And if the gas flow rate is reduced to maintain the pig’s speed, it will result in significant economic losses. Furthermore, for pipes of different diameters, cleaning pigs with appropriate speeds should be designed to improve the cleaning efficiency. Therefore, given the characteristics of cleaning natural gas pipelines, it is necessary to design pigs that can control speed. Currently, the real-time speed of the pig is primarily controlled through the speed-regulating device of the bypass valve. Abroad, extensive research has been conducted on the dynamic models of pig speed control devices; notably, Nguyen T T and others in South Korea achieved control over the bypass flow rate and speed of pigs under the assumption that the natural gas within the pig’s bypass passage is incompressible. Azevedo L F A et al. in Brazil developed a transient stagnation/sliding model by examining the effect of the bypass pore size on the dynamics of pigging devices. Podgorbunskikh A M and others from the Russian Academy of Sciences studied the design methods for speed control using an internal detector, the mechanism of speed control via a bypass valve, as well as the control circuit for the bypass valve, and designed an automatic speed control device for the internal detector equipped with a bypass valve. Regulating the speed of the pig through a bypass valve is effective, but it also presents certain technical challenges; for instance, such speed control devices only work optimally at certain flow rates of natural gas. If the flow rate of natural gas is too high, the deceleration effect is reduced due to the limited number of bypass passages available. Furthermore, such a speed control device requires components such as DC motors to be installed on the pig; it is necessary to ensure the safe operation of these components during pigging operations in the pipeline, for example by ensuring they can withstand pressure and are explosion-proof. At the same time, it is necessary to ensure that the power storage capacity of the battery components supplying electricity is sufficient for a long period. Overcoming these technical challenges can improve the cleaning efficiency and safety of pigging devices equipped with automatic speed control functions. Risks and countermeasures in the pigging operation of gas pipelines: Since the medium transported in gas pipelines is gas, pigging devices are required to have excellent sealing properties; otherwise, air leakage from the pigging device is likely to occur. This reduces the pressure difference before and after the pig, extending its operation time beyond the normal range. The solution to this problem is to replace the cleaning pig in a timely manner, thereby preventing severe wear due to prolonged use or delayed maintenance, which could lead to air leakage from the pig. The solution to the problem of pig blockage in natural gas pipelines is to increase the pressure behind the pig in order to force it to pass through the blocked area. If the blockage of the pig is severe, it is necessary to vent the natural gas surrounding the pig, cut out the blocked section of pipe, and remove the pig. If the pig breaks, operation is stopped, and another pig must be sent to push out the broken one. This article is reprinted from Jilin Province Zhaoxi Petroleum Technology Co., Ltd. http://www.jilinzhao*.com/