EXPERIMENTAL DETERMINATION OF FRACTURE CHARACTERISTICS OF WELDS FOR PRESSURE VESSEL MATERIAL

Abstract

Welds between different ferritic steels, such as SA508, SA516 etc and austenitic stainless steel, such as AISI type 304, 316 etc. are used widely in steam generation of nuclear power plants. Austenitic stainless steel tubes are used in the high temperature sections, such as final stage superheater and reheater. The other parts where temperature are lower, ferritic steels are used, which is more economical. 20MnMoNi55 grade German steel and austenitic steel (AISI 304) were joined by gas tungsten arc welding (GTAW) process using an austenitic stainless steel (AISI 308) filler metal. After welding, ultrasonic non-destructive testing was done in all the weld samples which ensured the defect free weld samples joints. Fatigue pre-cracking and J-resistance were experimentally evaluated by using compact tension and single edge bend (three point bend) specimens in nuclear welds. The unloading compliance technique was used to measure fracture characteristics during fracture test of compact tension specimen and single edge bend (three point bend) specimen. On the basis of result, the crack growth is more in the German steel base metal compared to austenitic stainless steel (AISI 304) base metal and austenitic stainless steel (AISI 308) weld metal. The JI value is higher in 20MnMoNi55 grade German steel base metal compared to austenitic stainless steel (AISI 304) base metal and austenitic stainless steel (AISI 308) weld metal. Similar JI value is also determined for (AISI 309L) buttering metal. Mechanical and metallographic properties of the specimens were obtained by. means of tensile testing micro hardness testing and scanning electron microscopy (SEM). Scanning electron microscope was used to observe the failure surfaces of fatigue pre-cracked and fractured surface.