Rust and Corrosion Prevention Hydraulic Fluid

Rust and Corrosion Prevention Hydraulic Fluid

Rust and corrosion prevention. Rust is a chemical reaction between water and ferrous metals. Corrosion is a chemical reaction between chemicals (usually acids) and metals. Water condensed from entrained air in a hydraulic system causes rust if the metal surfaces are not properly protected. In some cases water reacts with chemicals in a hydraulic fluid to produce acids that cause corrosion. The acids attack and remove particles from metal surfaces allowing the affected surfaces to leak, and in some cases to seize. To prevent rust, hydraulic fluids use rust inhibitors that deposit a protective film on metal surfaces. The film is virtually impervious to water and completely prevents rust once the film is established throughout the hydraulic system. Rust inhibitors are tested according to the ASTM D 665 Rusting Test.

This test subjects a steel rod to a mixture of oil and salt water that has been heated to 60C (140F). If the rod shows no sign of rust after 24 hours the fluid is considered satisfactory with respect to rust-inhibiting properties. In addition to rust inhibitors, additives must be used to prevent corrosion. These additives must exhibit excellent hydrolytic stability in the presence of water to prevent fluid breakdown and the acid formation that causes corrosion.