Identification of corrosion modes in steam pipes from the secondary system at Indian Point 2

Failure analysis of specimens removed from secondary side piping at Indian Point 2 was performed. The study included visual examination, wall thickness measurements, metallographic (optical and SEM) studies, and measurements of mechanical properties. Chemical analysis was carried out on the bulk metal, the surface region, and the overlying deposits. Oxide speciation was performed using XRD and Moessbauer spectroscopy. The results of the evaluation showed that erosion-corrosion was the principal pipe degradation mechanism. The factors contributing to significant erosion-corrosion were found to include a lower Cr content of the steel than needed to suppress erosion-corrosion, relatively low pH (8.8--9.2 during most of the period of plant operation), and high flow rates. The combination of these factors also gave rise to relatively high transport of iron oxides (predominantly magnetite) in the secondary system, which further increased the extent of erosion-corrosion. One important finding was the observation that magnetite particles in the wet steam were apparently responsible for the significant extent of erosion-corrosion of the pipes.