Memory effect and recoverability of passive film degradation of Alloy 800 in simulated crevice chemistry

• “Memory” effect was evaluated via comparing the pitting incubation time.
• Alloy 800 tubing material had some limited memory effect on passivity degradation.
• Damages of passive film were accumulative if the recovery time was short enough.
• A threshold time of chemical excursions was observed for the recoverability.

The degradation process of Alloy 800 under simulated steam generator (SG) secondary-side crevice-chemistry conditions containing chloride and thiosulphate was investigated. The SG chemical excursions were simulated by applying a series of square wave potential, followed by various periods of recovery. The results indicated that the damage to the passive film on Alloy 800 tubing material, caused by the excursions, was cumulative if the recovery time was no more than 900 s. The damage to the passive film of Alloy 800 was recoverable if the chemical excursions were shorter than a threshold value even after initiation of pitting/localized corrosion.