STUDIES ON FATIGUE CRACK GROWTH CHRACTERISTICS OF WELD JOINTS OF LARGE STRUCTURAL STEEL PIPES

Abstract

Welding of large structural steel pipe (material .SA333, Gr.6) of outer diameter 400 mm and wall thickness 32 mm, carried out by standard welding procedures using GTAW and SMAW processes. At various stages of welding NDT was carried out as per ASME specifications. The weld joints were post weld heat treated at 620 ± 10°C inside an electrical muffle furnace. Specimens for metallographic studies FGCR testing and tensile tests were properly macined out and sectioned from both base and weld metal. Test were carried out for knowing tensile data, inclusion content, grain size measurement, microstructural study and fatigue crack growth rate behaviour. All the testing was done as per proper ASME standards. Microstructure study revealed that weld region is composed of mixture of primarily bainite and pearlite. Reheat refined region is primarily composed of bainite and pearlite and HAZ region close to fusion line composed of bainitic transformation. FCGR tests shows that value of m increses while value of c decreases with increasing stress ratio. Life prediction analysis shows that for same AK, number of cycles taken for failure are less at higher stress ratio