Corrosion and Galvanic Behavior of Copper and Copper-Brazed Joints in Heavy Brine Lithium Bromide Solutions

The objective of the present work was to study systematically the corrosion resistance of copper-brazed joints in 400, 700, and 850 g/L, and commercial lithium bromide (LiBr) heavy brine solutions at 25°C, using electrochemical measurements. The filler metal tested was Cu-P (92.8% Cu, 7.2% P). The influence of the welding process on the corrosion resistance was studied on three different geometrical types of electrodes. Corrosion resistance was estimated from the polarization curves, comparing values of open-circuit potential (E_OCP) and calculating corrosion potentials and current rates using the Tafel slopes method. Critical potentials were calculated at 100 mA/cm². Inhibitor effects were analyzed in the commercial solution and the galvanic effect of the coupled base material and brazed joint was studied using the mixed potential theory. Phosphorus addition to the filler metal reduces the corrosion rate of this alloy and the corrosion rate of the simulated brazed joint. Chromate (Li₂CrO₄) and lithium hydroxide (LiOH) in commercial LiBr solution produce complete corrosion inhibition on simulated brazed joints. Copper may be the anodic or cathodic element when coupled to Cu-P filler metal depending on the LiBr solution. Oxides formed on the joints during the brazing process contribute to the corrosion acceleration of the brazes when they are galvanically coupled to copper. By contrast, when those oxides are removed from the surface, the brazed joint behaves as the cathode of the pair.