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Geothermal brines often contain high amounts of lead and copper ions that can precipitate as native Cu and Pb as consequence of galvanic corrosion when brines react with carbon steel materials. This contribution evaluates which materials could overcome the problem of galvanic corrosion at geothermal environment.
The behavior of these materials in water containing high chloride concentration (> 100 g/L NaCl) as well as various amounts of dissolved bCl2 and/or CuCl2 was characterized by electrochemical and exposure measurements.
Both methods reveal carbon steel suffers corrosion susceptibility, accompanied by Cu◦ and/or Pb◦ precipitation on the surface. Electrochemical measurements on stainless steels result in significant difference in corrosion and repassivation potentials (Ecorr = -189 mV, Erep = 70 mV), indicating a good corrosion resistance.
The passivation behavior of alloy 31 was investigated as a function of passivation potential in a green-death solution at 40 °C. The alloy 31 surface is in a stable passive state during cyclic potentiodynamic polarization. In potentiostatic polarization of alloy 31, passive current density increases with an increase in the passivation potential. Electrochemical impedance spectroscopy (EIS) and Mott–Schottky (M–S) analysis showed that a more defective n-type semiconductive passive film forms as the potential increases. X-ray photoelectron spectroscopy (XPS) revealed that passive film consists of mainly chromium and minor iron and nickel oxides. The increase of the applied potential is considered to be a reason for the change in passive film stability.