Recently, there has been a need to carry out work on deepening the pipeline (plunging) in some areas, where the depth of pipeline location was found to be inconsistent with the relevant standards. That is, pipelines during operation can be partially opened as a result of soil erosion, and they also tend to lose stability as a result of various factors (pressure, temperature, soil water content, etc.) and rise up (float). Also, the facts of laying pipelines in the process of their construction not to the design marks are known, due to the "low" construction conduct, that is, when the pipeline in some sections was in a trench, the depth of which did not correspond to the project. Further operation of such pipelines may be under the threat of the pipeline coming to the surface and mechanical damage to the insulation and the pipe body. Therefore, to ensure reliable operation of the pipeline, which has got raised sections, it is necessary to lower these sections to the design marks. To do this, it is necessary to develop equipmentand technology for repair work of this type. Therefore, the article considers two options for post-trenchingpipelines: lowering under its own weight without supporting and lowering with the maintenance of the pipeline by a supporting machine. For both methods of plunging, the stress-strain state of the pipeline was simulated during its lowering to the design level on the created mathematical model. An algorithm for calculating the geometric parameters of work performance, determining the stress state and checking the strength of the pipeline has been proposed.

The prevention of natural and man-made emergencies, which can be accompanied by numerous numan and material losses and disruption of living conditions, is one of the important nowadays problems and needs to be studied. The pipeline transport of hydrocarbons constitutes a significant man-made hazard. One way to reduce the risk of emergencies at pipeline facilities is to identify potential sources of danger in a manner of potentially hazardous objects certification. It is also known that any renovation, refurbishment of gas and oil pipeline facilities as well as theirs intended end-use alteration require proper identification and declaration of theirs safety. There has been recently being a very high need in compressor stations switching lines reconstruction that often is accompanied by construction of the appropriate connection branches of the pipeline in order to implement reversed transportation of natural gas and these objects should be consequently identified. Thus, the analysis regarding existing methods of higher danger objects identification for pipeline transport and the total mass evaluation of hazardous substances for such objects is provided. It is established that the existing models do not take into account the gas compressibility factor, the pressure drop in the gas pipeline after section cut-off, the size of the equivalent diameter of leaks and some others. A model is proposed to determine the total mass of gas contained in a section of a pipeline between linear shutdown valves and the mass of gas that can be lost over a time required to detect a leakage and close linear shutdown valves. As a result of proposed model implementation a newly built connection branch between the main line and the inlet of the compressor station, being constructed for reversed gas transportation implementation, was identified as a potentially dangerous object.