| Abstrakt: |
In the work on the examples of failure of four pipelines, the authors considered and analyzed the causes of failure of circumferential welded butt joints of main gas pipelines with a long-term service life with a diameter of 530...1420 mm from low-alloy ferritic-perlitic steels of grades 17G1S, 17GS and 15GSTYu, constructed back at the end of the twentieth century. Technical experts assume that, as a rule, accidents are associated with the failure of circumferential butt welded joints produced during assembly. Literature sources give quite limited reliable information about the causes of defects formation that lead to the failure of site welded joints. The authors show that even having provided satisfactory mechanical properties of steels and at the absence of deviations in the chemical composition of welded joints, depressurization of pipelines occurred due to weakening of the weld as a result of defects formation during operation or during construction and assembly works. The defects include pores, lacks of fusion, lacks of penetration, displacement of edges, use of backup elements, etc. that have not been detected by non-destructive testing methods. The obtained results made it possible to adjust a set of technological recommendations on the requirements and rules for performing assembly and welding works during the construction and repair of main pipelines in Ukraine over the last 20 years. 10 Ref., 2 Tabl., 7 Fig. [ABSTRACT FROM AUTHOR] |
