Abstract

Prediction of residual stresses in welds is essential in order to evaluate the integrity of a component subject to degradation mechanisms such as Stress Corrosion Cracking. During welding operations, complex thermo-mechanical and metallurgical processes take place and lead to microstructural changes such as dynamic recovery and dynamic recrystallization. These microstructural changes induce a modification of hardening behavior that should be taken into account to accurately evaluate residual stresses through numerical simulations. In the as-welded conditions, multi-pass pipe circumferential butt welds made of austenitic stainless steel show a typical residual stress profile through the wall of the welded joint. Such a shell bending profile places the inner half of the weld joint wall and its vicinity in compression in the axial direction. However, tensile zones can appear in the inner wall near the axis of the weld.

A large simulation campaign was carried out in order to cover different welding configurations and confirm these trends. This digital chart is built on the basis of a design of experiments of 100 Numerical Simulations of Welding per diameter and schedule. The parameters are:

- Diameter, thickness,

- Welding processes (GTAW, SMAW...),

- Groove shape.

This set of simulations show the systematic presence of a compression zone on the inner side, with some variability depending on the welding conditions and geometry. The classification of SCC risk is then defined by a set of two indicators that can be related to crack initiation (stress, strain hardening near the surface) and propagation (stress, strain hardening in the bulk). Considering in service loads in addition to realistic Weld Residual Stresses (WRS) makes Stress Intensity Factor (SIF) analysis feasible considering idealized crack position and orientation.

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