Mechanical properties of high ductility stainless steel for HVAC refrigerant piping

Abstract

This study investigates the mechanical and fatigue properties of PossFD, a stainless steel developed for high ductility as an alternative to copper pipes in HVAC refrigerant piping systems. Tensile and fatigue tests were conducted on both the base material and cross-weld specimens to account for property changes during pipe manufacturing. Cross-weld specimens, which include the base, weld and heat-affected zone, were used to evaluate the mechanical behavior of the welded sections. The base material of PossFD exhibited reduced tensile and yield strength compared to STS304, confirming its enhanced ductility. For the cross-weld specimens, tensile strength decreased while yield strength increased due to plastic hardening and thermal softening effects during fabrication. Bending load tests revealed that PossFD pipes require approximately 83 % of the load needed for copper pipes, despite their reduced thickness, demonstrating their suitability for pipe bending applications without compromising load capacity. Fatigue tests generated S-N curves for both the base material and cross-weld sections, with the welded specimens showing a lower endurance limit consistent with typical steel fatigue behavior. Finite element analysis and theoretical calculations were performed to evaluate the fatigue life of PossFD tubes under operating conditions involving internal pressure and thermal gradients. The results indicated that PossFD tubes operate within the infinite life range, suggesting their feasibility as a reliable alternative to copper pipes in HVAC refrigerant piping systems.