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Purpose. Ensuring the optimal mode of gas transportation from local sections of the main gas trunkline (GT), subject to repair (maintenance) and/or shutdown, to existing main gas trunkline based on the calculation, determination, and establishment of rational values of the operating modes of mobile compressor stations during the entire time of gas pumping. Methodology. The studies are based on existing physical principles and laws that describe the effect of the properties of natural gas and the geometric parameters of pipelines through which gas is pumped on the dynamics of changes in the mass and pressure of the transported gas. The calculation of the change in the mass and pressure of the gas in the gas pipeline from which the gas is pumped is based on a number of existing theoretical and empirical dependencies included in the generally accepted methods for their calculation. Known physical relationships and mathematical models are used to carry out the calculations. Findings. The mass approach to the issue of calculating the gas transportation time is more mathematically accurate than the volumetric one. The ratio of the relative mass to the relative gas pressure in a localized section of the main gas pipeline, during the entire pumping time, is a constant value. The use of the values of the quantities obtained at the point of intersection of the graphs of changes in the relative mass and relative pressure of the gas, in the preliminary calculation of the time for pumping gas, or pressure, or mass, or the volume of gas in each time interval, makes it possible to select the optimal rate of building up/reducing gas pressure by compressor units and optimal modes of gas transportation by operating gas pipelines during the operation of mobile compressor stations. Originality. The proposed approach to calculating and determining the time of gas pumping by mobile compressor stations from local sections of the main gas pipelines subject to repair (maintenance) and/or shutdown to sections of existing main gas pipelines proves that it is advisable to establish stable patterns in the transportation of natural gas using reciprocating compressor units only after modeling in time the change in the mass and pressure of gas in the local section of the main gas pipeline from which the gas is pumped. Practical value. The proposed approach to optimizing the time of gas pumping by mobile compressor stations makes it possible to increase the level of energy and resource efficiency of gas transmission enterprises, as well as to improve the technical and economic indicators of technologies for repairing the main gas pipelines, compressor stations of main gas pipelines associated with the need to bleed gas from sections of the main (technological) pipelines subject to repair (maintenance) and/or shutdown. Optimization of gas pumping time significantly reduces the time spent by employees of gas transmission enterprises under the influence of hazardous and harmful production factors, thereby reducing the level of relevant risks. Gas emissions and associated risks are reduced by 90%.

Any gas-main pipeline presents a technological complex of objects that functions as a single system, where all objects of the gas-main pipeline are classified as hazardous facilities, for which most of the existing risks are typical. In order to maintain a gas-transport system in operational, standard and safe condition, it is necessary to perform repair (routine) work assuming replacement or repair of defective sections of the pipe (or other equipment). The methods which an operator of a gas-transport system uses today for ensuring safety of such repair (routine) work are either environmentally harmful (“bleed” of gas), or hazardous and inefficient by energy and/or resource (“bleed” of gas, gas utilization, increasing of pipeline bearing capacity, "overlaying-welding" of defects under pressure, etc.). With this scheme of technological process, level of working and environmental safety and energy-resource efficiency of gas-transport enterprises sharply decreases. The purpose of our research was to propose a risk-oriented approach to the problem of working safety and energy resource efficiency of the gas-transport enterprises. The only type of repair, with which operational (safe) state and resource of the pipeline system can be fully restored is replacement of defective pipe or its section. Therefore, at the stage of preparatory work, the most acute problem is discharge of natural gas from the local section of pipelines by means of its pumping-over (accumulation) instead of "bleeding" or "utilization". We propose a rational, effective and risk-oriented approach to the use of mobile compressor units for pumping over (evacuating) of natural gas as a method for improving working safety and energy efficiency of the gas-transport enterprises. The proposed approach allows the gas-transport companies to create quickly an automated risk management system and reduce the risk level and, as a result, to improve working safety and energy efficiency of the processes of gas transportation.