MICROSTRUCTURAL CHARACTERIZATION OF PRIMARY WATER STRESS-CORROSION CRACKS IN ALLOY 182 WELDS FROM PWR COMPONENTS AND LABORATORY TESTS

摘要

Intergranular stress-corrosion cracking of Alloy 182 welds in PWR primary water service was investigated by analytical electron microscopy of cracks and their leading grain boundaries. Samples from crack-growth tests with simulated PWR and BWR water were also examined for comparison with service samples from several different PWRs. Observations of the crack-tip microstructures indicated that the cracking followed narrow (nm-scale) attack along carbide particle-decorated grain boundaries and carbide particle/matrix interfaces in the weld metal. Characteristic corrosion microstructures observed in the service samples included oxidized and partially dissolved carbide particles near the crack tips, and 5- to 8-nm-wide oxide-filled corrosion 'tunnels' along dislocations that had been intersected by cracks. Similar microstructures were found in the laboratory sample tested with simulated PWR primary water.