The effect of sulfur and lead on the corrosion of steam generator tubes made of alloy 690 thermally treated exposed to a wet steam environment at 320 °C

The corrosion behavior of thermally treated (TT) alloy 690 steam generator (SG) tubes was studied in a wet steam environment at 320 °C with the addition of S and Pb. These pollutants are known to accumulate in heat transfer crevices in SGs and can contribute to stress corrosion cracking (SCC). Oxide penetrations were observed at the oxide-metal interface in both S-only and Pb/S-polluted environments. Characterization by transmission electron microscopy (TEM) revealed a growth of the oxide penetrations along {111} slip planes of the alloy and traces of S and Pb at the oxide-metal interface. Characterization results have enabled us to propose a model to explain the formation of these oxide penetrations and the potential role of Pb and S on them.