The Swedish Radiation Safety Authority (SSM) and the Swedish nuclear power plant owners have financed Inspecta Technology in Sweden to analyze stainless steel pipe welds to obtain good estimations of weld residual stress (WRS) distributions. Detailed knowledge of the residual stress field in different types of welds is important since they can have substantial influence on degradation mechanisms such as stress corrosion cracking and fatigue. Residual stresses also have to be considered when assessing safety margins for failure by fracture.
The primary objective has been to update the recommended weld residual stresses for stainless steel pipe butt-welds, based on new knowledge on heat source modelling, material properties for high temperatures and material constitutive modeling.
Recommended through-thickness weld residual stress distributions have been developed. Detailed numerical welding simulations have been performed by using 2-dimensinal finite element technique for a set of cases covering most stainless steel pipe welds in Swedish nuclear power plants, together with sensitivity studies with respect to material modelling, pipe geometry and heat input. Best-estimate typical data have been used for influencing parameters with the aim to establish realistic through-thickness stress distributions to be applied in structural integrity assessments, especially for stress corrosion crack growth. Recommended residual stresses are presented along paths in the center line of the weld and in the heat affected zones. The recommended stress profiles are given as polynomials for each analyzed weld case. For intermediate geometries it is recommended to apply linear interpolation. Compared to earlier recommendations the axial residual stress profiles generally show a stronger trend for sinus type distributions.