Dynamics of movement of a smart pig in a low pressure gas pipeline
Currently, diagnostics of gas pipelines is carried out by in-line smart pigs driven by the pumped gas without changing the operating mode of the pipeline. A necessary condition for high-quality diagnostics is the constant velocity of the pig. If the pipeline does not contain inhomogeneities (plugs), then the steady movement of the smart pig occurs at a constant speed. However, in the presence of inhomogeneities, the movement becomes uneven, and the lower the pressure in the pipeline, the greater the inhomogeneity of the pig movement. From experience, it is known that to ensure a constant velocity of the pig, the required pressure inside the pipeline must be at least 30 atm. In pipe-lines for associated petroleum gas, the pressure usually does not exceed 10 atm. With the tightening of environmental regulations for the operation of oil fields in Russia, several thousand kilometers of gas pipelines for associated petroleum gas have appeared, and the problem of their diagnosis is urgent. In this article, the analysis of the physical processes accompanying the smart pig’s movement allowed us to obtain equations describing its movement, and to make estimates of the interaction of the pig with the plugs inside the gas pipeline. The concept of a new pig for a low-pressure associated petroleum gas pipeline is proposed, and the main methods of controlling its movement are established and justified.