Computational Method for Assessing the Crack Resistance of Elements of Gas Transmission System Structure

The kinetics of the occurrence and development of structural elements corrosion fatigue damages of Gas transmission system (GTS), operating under the complex influence of external factors with their various numbers and combinations, is considered. Taking into account the location of the GTS in an open area and the cyclical nature of the action of external factors, the dominant type of total loading of pipelines is one-sided variable bending, which causes corrosion and fatigue damage along the perimeter of the transverse annular section of pipes. At the same time, a significant service life and round the clock operation of pipelines, in addition to ensuring their fatigue strength, also requires calculations of the crack resistance of pipes. The calculated schemes of crack resistance are studied and the equation of the stress intensity coefficient \(K_{fc}\) is chosen. It is shown that this function gives reliable results with static and low-cycle loading of pipelines, but during multi-cycle loading, taking into account the kinetics of fatigue crack development, which leads to a change in the parameters, as well shapes and location of the break area, the application of this equation becomes conditional, requiring its correction taking into account variations in maximum stresses \(\sigma_{{p{\kern 1pt} \max }}\) , the depth of crack propagation \(a_{fc}\) , as well as geometric parameters, forms and location of fatigue break area. A new function has been obtained that makes it possible to clarify the \(K_{fc}\) values and determine the equivalent durability \(N_{e}\) of the structure, taking into account the presence of a fatigue crack \(a_{fc}\) and give quantitative assessment of the process of fatigue failure of the elements of the GTS structure.