Load-carrying capacity of straight-seam large diameter pipes with defects at the fusion boundary of the welded joint

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Load-carrying capacity of straight-seam large diameter pipes with defects at the fusion boundary of the welded joint

Dilman, V.L. / Ostsemin, A.A. / Voronin, A.A.

Investigations are carried out into the effect of non-continuous (surface and internal) crack-like defects situated at the fusion boundary between the parent metal and the weld metal on the strength of welded joints in large-diameter pipes. The theoretical analysis is based on the method of slip lines under static tensile loading in the plane strain conditions. The calculation equations are derived for evaluating the stress state and strength of the welded joints. It is assumed that the net section of the welded joint is in the general yielding condition, whereas the parent metal of the pipe operates by the elastic mechanism. Consequently, axial deformation of the welded joint is low in comparison with circumferential deformation and, consequently, the effect of residual welding stresses may be ignored. Attention is given to the moment of the loss of general plastic stability of the hard part of the joint in the net section (i.e. the start of uniform unstable deformation) where the level of deformation increases with constant external loading. The effect of the volume stress state is taken into account by the stiffness parameter. For examining the stress-strain state of the heterogeneous joint in the net section in the vicinity of the fusion line, attention is given to a specimen consisting of two homogeneous and isotropic sections with different plasticity parameters. The specimen is subjected to the effect of a tensile stress in the direction normal to the contact surface. In the case of thick hard interlayers, the relative maximum size of the defect at which the strength of the joint does not decrease in comparison with the defect-free joint is independent of the position of the defect at the fusion boundary.