Monitoring of the linear section strength reliability is carried out continuously throughout the entire life cycle of the main gas pipelines. One of the main indicators allowing to assess the current reliability of the inspected section is the probability of its trouble-free operation. Significant influence on the value of this indicator is exerted by the excessive internal pressure and temperature drop in the inspected section. These parameters are related to basic and included in all the probabilistic models, on which the methods of calculating reliability indicators are based. The random nature of the significant parameters is the reason that the probabilistic regularities of excessive internal pressure and temperature drop are subject to changes of technical, physical and natural nature over time. Hence, the monitoring results will also change and reflect for each section of the linear part that level of reliability, which corresponds to the period of collection and processing of the relevant input data.

For ensuring safe operation of the main gas pipelines, based on the monitoring results it is important to establish differences in values of safety reliability indicators within the limits of the same sections in different time periods.  The current values of these indicators are taken as a criterion to clarify, and in some cases, change the strategy of operation, maintenance or repair of the linear part of the gas pipeline, adopted on the basis of previous values. At the same time, there are risks of making wrong technical decisions on further operation based on the results of actual assessment of the reliability of the inspected sections. The reason for such risks is the probability of situation occurrence when the reliability of the inspected section determined based on the current values of the significant parameters is higher than for the previous historical periods, despite the increase in the gas pipeline service life.

The article presents the monitoring results testifying significant differences in the reliability indicators of gas pipeline sections, which are obtained based on the individual regularities of the distribution of significant parameters identified for the inspected areas in different periods of time during the operation phase.