The effect of the weld thermal cycle on the microstructure and corrosion resistance of alloys 690, 600 and 800

The heat exchanger tubing materials used in the steam generators of water reactor design nuclear power plant have been a major area of concern. Tube failures have occurred due to a range of corrosion mechanisms (IGA, SCC etc). Continued development of materials with microstructures and compositions designed to withstand the environments met in water reactor operation has increased the reliability of the components. During steam generator fabrication, the tubes are welded into position, the methods and materials used giving rise to changes from the optimized microstructures and compositions. This paper reports on the programme of work currently being undertaken, primarily to investigate the effect of this weld thermal cycle on the microstructure and corrosion resistance of alloy 690 tubing welding to alloy 82 clad ferritic tubesheet-alloys 600 and 800 are also being studied for comparative purposes