FRACTURE TOUGHNESS OF WELD JOINT OF LARGE STRUCTURAL STEEL PIPE

Abstract

In this work studied were carried out on carbon steel pipes of material SA333 gr.6. Pipe were welded using GTAW & SMAW processes. Specimens were prepared for J-intergra testing, notch tensile testing, Charpy impact energy testing. Specimens were prepared from both base and weld metal. For metallographic studies one specimen from each weld was prepared. All the test were carried out at room temperature. Inclusion content grain size measurement and micro structural, studied were carried out metallographic specimens. Fracture toughness tests revealed J initiation value of weld was less than base metal. Notch tensile test also showed less notch strength ratio of weld metal than base metal. Charpy impact energy results showed higher impact energy for base metal than weld metal. Ramber Osgood equation coefficients were calculated. Value of n increased in weld and value of a .decreased. These, all the tests revealed the fracture toughness of weld - to the lower than base metal. These results were further interpreted by microstructural studies. Bainitic transformation in weld metal zone along with high inclusion content, coarser grain size and presence of weld defects caused relatively lower fracture toughness. An attempt was also made for safety assessment of nuclear pressure vessels using deformation plasticity based failure assessment curves. It showed high resistance of this material to tearing instability even in the presence of deep