Ivanchuk O. Diagnostics of stressed state and estimation of safety margin of circumferential welded joints of different thickness pipes of main oil/gas pipelines.

The dissertation is devoted to the development of design-experimental method for determining of residual stresses in zones of circumferential welded joints of different thickness pipes and for estimation of their influence on static strength of segments of pipeline with such joints, sharp-ended defects like cracks being present in them. Within the shell theory, a mathematical model is developed which describes the axis-symmetrical stressed state of welded pipes of different thickness under the influence of localized near a joint residual non-compartible deformations. The determination of residual stresses is based on solutions of inverse problems of the theory of shells with inner stresses, information from experiments based on non-destructive methods being used. Using the diagram of fracture estimation which is based on fracture mechanics, the effect of residual stresses on safety factors of pipeline segment with a welded joint and with an internal semi-elliptical surface crack in the wall of the thiner pipe under internal pressure is estimated.