Temperbead Welding Repair of Nuclear Components

As part of a research project, AREVA NP assessed a Temperbead welding process as a mean to repair nuclear components such as pressurizers of PWR (Pressurized Water Reactors). This technique allows to perform repairs without the need of PWHT (post weld heat treatments) without compromising the microstructure and mechanical properties of the repair and the heat affected zone (HAZ) of the low alloy steel component.

The studied "Temperbead" process aims at repairing a potential non acceptable indication within the stainless steel weld metal of a dissimilar metal weld between the safe-end nozzle and the pressurizer low alloy steel nozzle on the outer diameter of the nozzle due to corrosion. The repair process uses an alloy 82 filler metal and the Gas Tungsten Arc Welding (GTAW) automatic welding process, preheat and post heat treatments were implemented during the repairing process. A representative mock-up of the repair was fabricated in order to verify the effectiveness of the repair technique, and a full characterization of mechanical properties, microstructure and residual stresses was carried out. The paper focuses on the mechanical and metallurgical properties of the repair and gives some results of residual stress measurements using the incremental deep hole drilling technique. 

Results show that the Vickers hardness and the microstructure of the HAZ under the Temperbead repair are equivalent to those of conventional repairs. In addition, Charpy impact toughness, and tearing resistance testing at 300°C in the HAZ under the Temperbead repair and in the HAZ near the original stainless steel weld metal show excellent values. This means that repairs of nuclear components are viable using the Temperbead repair technique without compromising the integrity of such components. The repair methodology can be extended to other components of the nuclear island.