Factors affecting pit progression in Inconel Alloy 600 steam generator tubes

Pit growth in commercial Inconel Alloy 600 steam generator tubes is studied as a function of secondary water contaminant concentrations and combinations at typical operating temperatures. The contaminants that have been chosen in this study are the cupric, chloride and sulfate ions. The main objective is to determine the aggressive ion species or combination which affect the pit propagation process in commercial mill-annealed alloy 600 steam generator tubing in the range of simulated concentrations (concentration factor: 10;The pitting corrosion experiments performed consist of three main parts: (1) an isothermal capsule test, (2) a static autoclave test and (3) a cyclic potentiodynamic measurement.;The test results show a dependence of pit depth on the Cl;Pit aspect ratio (depth/width) and the amount of pit corrosion product depend primarily Cl;In most cases, the saturation of pit growth is observed indicating repassivation of growing pits. However, the reactivation process of a passivated pit seems to be associated with the development of secondary micropits.;It is postulated that the pit growth resistance (or pit growth sensitivity) consists of the pit growth rate and the degree of difficulty in arresting a growing pit. In this sense, a cyclic potentiodynamic measurement can determine the pit growth resistance of a material based on the pit growth sensitivity (PGS) established in this study.;Alloy 690 tubing shows poorer pitting resistance than alloy 600 tubing in terms of pit depth observed.