ИССЛЕДОВАНИЕ РАБОТОСПОСОБНОСТИ ПРОДОЛЬНЫХ СВАРНЫХ ШВОВ ТРУБ С ТРЕЩИНАМИ

The efficiency of pipeline system maintenance is largely determined by the reliability of the assessment of the operability of pipes with defects. Operating organizations usually use unified calculation schemes to determine the strength, durability, stability, etc. of pipelines with defects, which are divided by type of defect, but do not take into account the nature of the defect's origin, which can have a decisive impact on its current danger and further development. In particular, due to the detection of a large number of hot cracks in the longitudinal welds of pipes, the question arises about the expediency of using computational schemes for this type of defect, developed and tested for classical fatigue or deformation cracks of the base metal. This article presents the results of studies conducted to study the fracture resistance of welded joints with hot cracks of factory origin in the center of the weld. The object of the study was 4 templets containing defects of the specified type. Special model tests were carried out, which made it possible to reproduce a biaxial stress-strain state in the working area, similar to that which occurs in the pipeline when it is loaded with internal pressure. As a result of the tests, the development of real cracks up to 3 mm deep under cyclic loads significantly exceeding operational ones was not recorded. Taking into account the test base of 3·104 cycles, which corresponds to about 90 years of pipeline operation, the result obtained indicates a high resistance of the seam metal to the development of hot cracks. Four-point bending tests were also performed to destroy full-thickness samples with a crack-like stress concentrator in the center of the longitudinal weld. In all cases, the samples were destroyed along the weld fusion line, and no cracks were detected from the stress concentrators. The obtained result suggests the possibility of using special, less conservative standards of maintainability of welded joints with hot cracks of factory origin in the center of the longitudinal seam.