Development of Modified Alloy 52 Filler Metal for Nuclear Class 1 Components

Abstract Nickel-based 52 filler metals are used for welding of dissimilar metal joints in nuclear power plant components, such as a safe end weld of a reactor vessel nozzle, because of their high resistance to Primary Water Stress Corrosion Cracking (PWSCC). On the other hand, it is generally regarded that 52 filler metals tend to be inferior to conventional 82 filler metals in weldability. The typical concerns of 52 filler metals for weldability are susceptibility to hot cracking and the amount of oxide film on the weld bead surface. To improve the weldability, a modified 52 filler metal has been developed. The improved 52 filler metal, which reduces S, Zr, Al, Ti and Nb and adds Ta, satisfies AWS 5.14 ERNiCrFe-7A. Trans-varestraint, cladding, Gleeble, U-groove weld and dissimilar joint weld tests were performed, and the weldability of the improved 52 filler metal was confirmed. Ultrasonic tests were performed to the weld joints using the improved 52 filler metal and the conventional 52 filler metal, and the test results demonstrated that there was no significant difference between the two filler metals. PWSCC constant load tests and crack growth tests were performed to compare the PWSCC resistance, and the test results also demonstrated that there was no significant difference between the two filler metals. Welding procedure qualification tests were conducted for the modified 52 filler metal, and the test results satisfies the criteria.