Abstract
The galvanic corrosion behavior of Alloy 690 coupled with magnetite has been investigated in an alkaline solution at 30 °C and 60 °C using a potentiodynamic polarization method and a zero resistance ammeter. The positive current values were recorded in the galvanic couple and the corrosion potential of Alloy 690 was relatively lower. These results indicate that Alloy 690 behaves as the anode of the pair. The galvanic coupling between Alloy 690 and magnetite increased the corrosion rate of Alloy 690. The temperature increase led to an increase in the extent of galvanic effect and a decrease in the stability of passive film. Galvanic effect between Alloy 690 and magnetite is proposed as an additional factor accelerating the corrosion rate of Alloy 690 steam generator tubing in secondary water.
Highlights
Nickel-based Alloy 600 has been widely used as a steam generator (SG) heat transfer tubing material in pressurized water reactors (PWRs)
This study demonstrates that the corrosion rate of Alloy 690 increases by a galvanic couple with magnetite
The galvanic corrosion behavior of Alloy 690 coupled with magnetite in alkaline aqueous solutions was predicted by the mixed potential theory and verified by zero resistance ammetry (ZRA) measurements
Summary
Nickel-based Alloy 600 has been widely used as a steam generator (SG) heat transfer tubing material in pressurized water reactors (PWRs). Magnetite particles released from the surface of carbon steel piping are transported into an SG, accumulated on the top of tube sheet and deposited on the outer surface of SG tubes. These corrosion products reduce the efficiency of the SG by deterioration of the heat transfer and accelerate the corrosion of SG tubes [10,11,12]. The magnetite adhering to SG tubes distorts eddy current signals from the tubes during in-service inspection [15]
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