Effect of Aging on the Fatigue Crack Growth Behaviour of SS 316(N) Welds at Ambient Conditions

Abstract

Fabrication of reactor components using SS316LN involve welding as one of the major manufacturing processes. These welds are potential sources of defects, growth of which often becomes the life-limiting factor for the components during prolonged service exposures. Many of these components are subjected to flow-induced vibrations, leading to fatigue crack initiation and growth during the operation. It calls for the evaluation of fatigue crack growth (FCG) behavior of these welds as part of ensuring the structural integrity. The FCG resistance also degrades due to aging-induced microstructural changes. The effect of aging in the temperature range 643–823 K and after 20,000 h durations on FCG properties has been evaluated at ambient temperature (298 K). The variation in the ΔK threshold with ageing has been discussed in the light of microstructural observations. The maximum benefit of ageing on FCG properties was observed at 643 K due to the crack tip branching during crack growth. Finally, the FCG data of these welds were compared with the (Design and construction rules for mechanical components for mechanical components nuclear installations (2007) RCC-MR, Section I–subsection Z: Appendix A16, (Datasheet for Austenitic Stainless Steels) pp 219. https://www.afcen.com/en/rcc-mrx/98-rcc-mr-2007.html) codified data and have been found to be better than that of values specified in the codes.