Assessment of the s trength reliability of main pipelines sections is based on the integration into the calculation models of reliability indicators of probability patterns for the e xternal load acting on the examined section of the main pipelines linear part, and the s trength characteristics of the pipe m aterial used at the construction stage of this section. The experience accumulated to date in calculating reliability indicators allows us to conclude that these patterns are actually individual and specific for any part of the main pipeline linear part. Moreover, even within the same section, individual probabilistic patterns for the parameters of the e xternal load and ultimate stresses are changed during the lif e of the main pipeline.
The paper assesses the impact of changes in the statistical characteristics of the distribution of the yield strength of pipe steels on the s trength reliability of sections of main pipelines.
Materials and methods
Reliability Theory, Mathematical Statistics, Probability Theory
An analysis of the results allows us to conclude that changes in the patterns of distribution of the yield strength of 14KhGS pipe steel that occur after long-term operation of the main oil pipelines, in the first case, by five times, and in the second, by an order (~ 10 times) increase the probability of failure Q within examined areas. Therefore, such changes must be classified as degrading for the strength characteristics of 14KhGS pipe steel and this fact should be taken into account when solving the problems of assessing the strength reliability of sections of main oil pipelines, at the stage of construction or repair of which similar pipe products were used.
Changing the statistical characteristics of the distribution of the yield strength of pipe steel 14KhGS after long-term operation of the pipeline has a significant impact on the strength reliability of linear sections.
2. Deterministic methods do not allow to take into account, when assessing the strength of linear sections, degradation changes in the patterns of yield strength distribution of 14KhGS steel that occur as the pipeline service life increase.
3. The results obtained by assessing the impact of the duration of the operation of the pipeline on the reliability of linear sections indicate the need to study the probabilistic laws of strength characteristics for other grades of pipe steels.