ANALYSIS OF CAUSES OF FAILURE OF FIELD WELDED BUTT JOINTS OF MAIN PIPELINES AFTER LONG-TERM OPERATION.

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 and oil pipelines with a long-term service life of 530-1420 mm diameter 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 in field conditions. Literature sources give quite limited reliable information about the causes of defect formation that lead to the failure of field 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 defect formation during operation or during construction and assembly works. The defects include pores, lacks of fusion, lacks of penetration, edge displacement, use of embedded elements, etc. That were not 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. [ABSTRACT FROM AUTHOR]