Corrosion studies of 90Cu-10Ni alloy tubes in simulated sulfide-polluted seawater under dynamic flow conditions

A comprehensive corrosion study of two commercial 90Cu-10Ni alloy tubes, named Tube A and Tube B, in simulated sulfide-polluted seawater under dynamic flow conditions has been conducted to understand their service lives. Electrochemical techniques involving a rotating cylinder electrode were used to evaluate the effect of sulfide concentration on the corrosion behaviors of both tubes, while combined surface analytical techniques (SEM/EDS, XRD, and) were useful for the characterization of the corrosion product films on both tubes. Sulfide exhibited good corrosion inhibition abilities on both tubes under static flow condition (0 rpm). This is attributed to the spontaneous formation of protective film layers and the enrichment of the corrosion product films by the alloying elements. However, the inhibitive property gradually depleted with increasing flow speed due to the effect of hydrodynamic forces. Comparatively, due to the nature of the corrosion product films formed on the exposed surfaces of both tubes, Tube A demonstrated lower corrosion rates under static flow while Tube B exhibited lower corrosion rates at higher flow speeds. After 15 days exposure to the test system, the corrosion product films on both tubes were characterized to consist mainly of copper (I) sulfide (Cu 2 S), copper (II) sulfide (CuS), copper (I) oxide (Cu 2 O), nickel (II) hydroxide (Ni(OH) 2 ), nickel (II) oxide (NiO), nickel (III) oxide (Ni 2 O 3 ), and copper (ii) oxide (CuO). Furthermore, traces of copper (II) chloride (CuCl 2 ), copper (II) hydroxide (Cu(OH) 2 ), nickel (II) sulfide (NiS), iron (II) sulfide (FeS), and iron (I) sulfide (FeS 2 ) were also characterized. The mechanism of their formation and effects on the corrosion processes were also discussed.