An Analysis of Crack Resistance of a Main Pipeline Taking into Account Residual Welding Stresses

This paper describes methods and software tools for evaluating crack resistance of a main pipeline in the zone of butt-welded joints when the pipeline is in operation. The author’s finite-element software developed in Fortran Visual environment is used to calculate residual welding stresses. The calculations are based on the principles of nonlinear nonstationary heat transfer, modelling of phase and structural transformations, and thermo-elasto-plasticity. Boundary conditions of the third kind are used to describe the heat transfer. The transformation of austenite into ferrite and bainite under non-isothermal conditions is predicted using the theory of isokinetic reactions. Residual stresses are modelled by solving the thermo-elasto-plasticity problem for a material with unsteady structure. It is shown that longitudinal semi-elliptic edge cracks located on the internal surface of the pipe near the weld are the most dangerous from the point of view of brittle strength. Irvine force criterion of fracture forms the basis of crack resistance calculations. The maximum stress intensity factor at the crack front in the pipeline is calculated using ANSYS finite-element software. The results of the crack resistance analysis are presented as dependencies of the critical depth of the crack on the ratio of the half the length to the depth.

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