Friction and corrosion properties of water–glycol fire-retardant hydraulic fluids (HFCs) and their modifications

The energy crisis and environmental pollution are worsening. Therefore, water-based hydraulic fluids, i.e., aqueous ethylene-glycol-based, fire-retardant hydraulic fluid concentrates (HFCs), are becoming increasingly used. However, seawater intrusion inevitably occurs under marine conditions, generating hazards, such as corrosion and friction, within the hydraulic system components, pipelines, and materials. Moreover, HFCs have several drawbacks, including low viscosity, inadequate lubrication, and high corrosivity. Therefore, the tribological characteristics and corrosivity of HFCs must be improved and reduced, respectively. This can be achieved using additives. Herein, we summarize the fundamental characteristics of HFCs and their modifications for use in the marine environment, focusing on the optimal water–ethylene glycol proportion and its influence on the physicochemical, lubricating, and tribological properties of this HFC under varying conditions. We discuss the latest progress on the effect of seawater on the tribological corrosion of HFCs and the reduction of corrosivity in the presence of different additives. Finally, we highlight challenges and propose future research to improve performance in the marine environment.