Fatigue Behavior of Small Bore Piping Welded Joints under Vibration: Metallurgical and Nondestructive Evaluation

Abstract The integrity of small-bore piping welds, typically up to 50 mm in diameter, is crucial for reliable operation in industrial settings, particularly under vibration-induced stresses that can lead to fatigue failures. This study provided an in-depth analysis of the fatigue behavior of V-groove butt weld joints in small-bore steel piping systems under vibration conditions, focusing on the influence of various weld filler metals and base materials. An advanced experimental setup simulated dynamic vibrations to examine the effects of different welding wire compositions on fatigue strength, damage susceptibility, and fracture tendencies. Finite Element Analysis (FEA) was employed to investigate stress distributions, revealing significant stress concentrations and deviations from the acceptable fatigue limits defined by industry standards. The study utilized nondestructive testing methods, including magnetic particle inspection (MPI) and radiographic testing (RT) were used to identify and monitor weld discontinuities, emphasizing the importance of continuous inspection with these methods to ensure weld integrity under dynamic loading conditions. Microstructural analysis revealed that manganese-enriched welds promote acicular ferrite formation, enhancing hardness, while high nickel content increases discontinuities and lowers toughness. Optimal manganese levels (0.6–1.4 wt %) improve mechanical properties, but excessive manganese combined with nickel adversely affects fatigue performance. The study emphasized the need for optimized alloy composition and design to enhance fatigue resistance in small-bore pipe welds, offering insights for improving long-term reliability. This research deepened the understanding of vibration-induced fatigue and informed better design and maintenance protocols for steel piping systems.