Effect of heat input on the microstructure and toughness of welded API pipelines

Abstract

We seek to explain the weld toe-crack failure in terms of crack nucleation and propagation based on the observed phases and their size. Three welded joins were studied, varying the heat inputs in order to modify the weld microstructure. We work with an API X70 PSL2 pipeline steel, varying the ferritic size phases. We performed Charpy impact and Vickers hardness tests; we also determined the chemical composition (especially the oxygen percentage). Based on the relationship between the test results and the microstructure, we achieve a modification of the welded join microstructure and toughness, observing the heat-input effect in the weld oxygen diffusion as well as its effect in the type and size of the phase observed.