Galvanic Corrosion between Alloy 690 and Magnetite in Alkaline Aqueous Solutions

Abstract

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.

Micro-Galvanic Corrosion of Steam Generator Materials within Pores of Magnetite Flakes in Alkaline Solutions

“…Therefore, even if trace amount of Cu particles are present in the SG tube deposits, the Cu removal process should be included in the chemical cleaning process. As reported in many previous studies [4][5][6][7][8][9], this work again confirmed that magnetite accelerates the corrosion rate of SG materials by galvanic coupling. In addition, the results in this work had shown that metallic Cu and Pb as well as magnetite increased the corrosion rate of SG materials.…”

“…Recently, many investigations on the galvanic effect by magnetite on the corrosion behavior of secondary coolant system materials such as nickel-based alloys [4][5][6] and carbon steel [7][8][9] have been reported. It is well known that the SG deposits mainly consist of magnetite and are porous in nature [10,11].…”

“…Hence, an electric contact between SG structural materials and magnetite deposits could be occurred. In various secondary environments, it was reported that the corrosion potential of magnetite was higher than those of secondary system materials and the corrosion rate of the SG materials was greatly increased due to the shift in their potentials to the anodic direction [4][5][6][7][8][9]. Through the galvanic effect of magnetite on the SG materials, the mechanism on the galvanic corrosion of the secondary system materials coupled to magnetite is well established.…”

Corrosion Behavior of SA508 Coupled with and without Magnetite in EDTA-Based Solutions

“…Various methods for the manufacture of magnetite electrodes have been reported in the literature: casting molten magnetite [15,16], sintering magnetite powder [17,18], sputtering deposition [19], etc. However, a simpler method was recently developed to electrodeposit a magnetite layer onto carbon steel and Ni-based alloy substrates [20][21][22][23], and was verified to be useful for making electrochemical electrodes [4][5][6][7][8][9].…”

“…It has been reported that a galvanic coupling with magnetite accelerates the corrosion of secondary system materials: carbon steel [4][5][6], alloy 600 [7] and alloy 690 [8,9] in various environments simulating the secondary conditions of SGs. Most of the tubes and heated crevices in operating SGs are covered with deposits or sludge.…”