The influences of NO3- concentration and AC density on corrosion resistance of FeCoNi high entropy alloy in simulated saline-alkali soil solution were studied via a series of measurements. Related results imply that the anticorrosion property of the HEA is significantly improved with the increase in NO3- concentration, particularly at high concentration of 0.1 mol/L, and the passive film covering the HEA becomes dense, intact and uniform. NO3- as a protective barrier is absorbed on the film surface, significantly inhibiting the pitting corrosion of the HEA. As AC density rises, the HEA surface status evolves from passivation to activated state, presenting a serious overall corrosion feature. The AC application facilitates the damage of passivation film grown on the HEA, resulting in a rapid increase in the number of flaws, which remarkedly decreases its resistance capacity against corrosion. Furthermore, under the combined influence of the two factors, the adverse effect of AC interference is obviously larger than the positive impact of NO3- on the corrosion resistance of the HEA at i(AC) of 50 A/m(2), causing plentiful defects within the passive film and severe corrosion of FeCoNi HEA.

Carbon steel structures employed to convey hydrocarbons and other dangerous fluids, such as oil or flammable liquids, are equipped with degradation prevention systems, which typically consist of a cathodic protection (CP) system combined with an external insulating coating, both designed to reduce the corrosion rate below 10 mu m/year. The presence of electrical interference, both AC and DC, can cause significant corrosion damage to metallic structures, even when CP is applied. DC interference is determined by the presence of a third-party CP system or public transportation system. AC interference may occur through conduction or induction mechanisms, caused by high-voltage powerlines or high-speed trains, powered by AC. Both interferences may lead to localized corrosion at coating defects, despite compliance with the -0.850 V saturated Cu/CuSO4 reference electrode (CSE) protection criterion. Considering AC-induced corrosion, both field failures and laboratory investigations have demonstrated that corrosion can occur at industrial frequencies, and when CP is applied following the standards. Even though AC-induced degradation is generally not as severe as DC interference, uncertainties remain regarding the protection potential range necessary to achieve acceptable corrosion prevention under AC interference. To formulate a CP criterion under AC interference, weight loss measurements were conducted on carbon steel samples under cathodic protection in solutions that simulate real soil conditions. Carbon steel coupons protected by CP were interfered with AC densities ranging from 1 A/m(2) to 800 A/m(2) for four months. During this time interval, polarization potential, protection current density and AC density were monitored. Based on the experimental data gathered during this study, a proposal for a risk map is also suggested. The results indicate that overprotection (potentials < -1.2 V CSE) represents the most dangerous scenario when AC interference is involved.