Effect of seawater intrusion in water-glycol hydraulic fluid on the electrochemical corrosion behavior of carbon steel and stainless steel

Water-glycol hydraulic fluid (HFC) has been applied in deep-sea hydraulic systems owing to its flame retardant and environmental performance. However, the corrosion characteristics of metals in HFC have not been widely investigated. The electrochemical corrosion behavior of 45# steel and 17-4PH stainless steel in HFC containing four concentrations of seawater (0 %, 3 %, 11 %, 19 %) were evaluated by potentiodynamic polarizations (-800 mV similar to 1,500 mV vs. Hg/HgO), electrochemical impedance spectroscopy (EIS), potentiostatic polarizations (0.5 VHg/HgO) and immersion test (240 h). The research results indicate that a corrosion-resistant carbon film is formed on the surface of 17-4PH stainless steel and 45# steel in HFC. The infrared spectroscopy results suggest that the formation of the carbon film is due to the adsorption of the benzene ring of tolyltriazole (TTA) in HFC by the metal C. 45# steel exhibited stronger corrosion resistance than 17-4PH stainless steel due to the formation of a denser carbon film through high carbon content adsorption. The infiltration of seawater into HFC enhanced its corrosiveness by enhancing its conductivity and Cl- pitting on the C film. This research is significant as it sheds light on the corrosion behavior of metals in HFC, a crucial aspect in the design and maintenance of deep-sea hydraulic systems.