EXPERIMENTAL EVALUATION OF FRACTURE CHARACTERISTICS OF NUCLEAR WELD USING COMPACT TENSION SPECIMEN

Abstract

Fatigue pre-cracking and J-resistance were experimentally evaluated by using compact.tension specimen in nuclear weld. Welds between different ferritic steels, such as SA 508, SA 516 etc. and austenitic stainless steels, such as AISI type 304, 316 etc. are used widely in steam generators of nuclear power plants. Austenitic stainless steel tubes are used in the high temperature sections, such as final stage of superheater and reheater. The other parts where temperatures are lower, ferritic steels are used, which is more economical. A german steel and austenitic stainless steel (NISI 304) were joined by gas tungsten are 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. The unloading compliance technique was used to measure fracture characteristics during fracture test of compact tension 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 the german steel base metal compared to austenitic stainless steel (AISI 304) base metal and austenitic stainless steel (AISI 308) weld metal. Mechanical and metallographic properties of the specimens were obtained by means of microhardness testing, tensile testing, charpy impact testing and scanning electron microscopy (SEM). Scanning electron microscope was used to observe the fracture surfaces of fatigue pre-cracking, fracture surface and charpy impact test specimens. iii