Hydraulic fluid is specifically engineered to transmit power within machinery, acting as the lifeblood of systems ranging from construction equipment to aircraft controls. These fluids, whether mineral oil-based, synthetic, or water-glycol blends, must be highly stable to perform under extreme pressure and temperature. The question of whether this fluid is corrosive is complex, depending heavily on the fluid’s base composition and its condition within the system. High-quality fluids are formulated to protect system components, but contamination or degradation can quickly alter their chemical nature.
Corrosivity vs. Chemical Aggressiveness
Corrosivity is defined as a fluid’s ability to chemically degrade metals through an electrochemical reaction, often associated with a high or low pH level. Modern hydraulic fluids are engineered to be non-corrosive to the system’s metals under normal operating conditions. They contain rust and oxidation inhibitors that form a protective film on metal surfaces, and standard industry tests ensure new fluid will not chemically attack common metals such as steel or copper.
The true danger often comes from chemical aggressiveness, a broader term encompassing degradation not solely dependent on pH. High operating temperatures accelerate the fluid’s oxidation, leading to the formation of organic acids and gums that are chemically aggressive to components. This process breaks down the fluid’s protective additives, allowing rust and verdigris to form on steel and copper parts.
The most common cause of a fluid becoming corrosive is water contamination, which enters the system through seals or condensation. Water reacts with certain additives, reducing their stability and creating an electrolyte that initiates electrochemical corrosion on metal surfaces. This reaction forms acidic by-products that weaken the oil’s oxidation resistance, leading to degradation of internal parts like pump housings and cylinder walls.
Material Compatibility and Degradation
A hydraulic fluid’s chemical aggressiveness is most evident in its interaction with non-metal components, leading to material degradation. The primary damage to seals and hoses, typically made of elastomers, is a physical change caused by solvent action, not corrosion. This action can manifest as the material softening and swelling, or conversely, hardening and cracking, depending on the specific elastomer and fluid type.
Nitrile rubber (NBR) is compatible with petroleum-based hydraulic oils but is not recommended for use with phosphate ester fluids, which cause significant degradation. Conversely, Ethylenepropylene rubber (EPDM) is highly recommended for phosphate ester fluids but is incompatible with petroleum oils. This necessity for precise material matching highlights the fluid’s chemical aggressiveness toward incompatible components.
Certain metal alloys also experience degradation when an incompatible fluid is used or when additives break down. Components containing yellow metals, such as brass or bronze, are sensitive to corrosive attack when the fluid deteriorates. This is often exacerbated by the breakdown of zinc-based anti-wear additives in the presence of water and heat.
Safety, Exposure, and Handling
From a personal safety standpoint, hydraulic fluid is not a classic corrosive agent to human tissue, but it is a severe irritant. Direct skin contact can cause irritation, rashes, or dryness, while prolonged exposure leads to dermatological issues. Inhaling the vapors or mist from heated hydraulic fluids, especially those with synthetic additives, can cause respiratory irritation, headaches, and dizziness.
The most immediate and severe danger is a high-pressure injection injury, which occurs when fluid penetrates the skin through a pinhole leak in a pressurized line. Even a small amount of injected fluid can cause severe internal tissue damage, sometimes leading to the loss of a limb, requiring immediate medical attention. Basic personal protective equipment (PPE) is mandatory when handling these fluids. Workers should wear chemical-resistant gloves, such as nitrile, and safety goggles or a face shield to prevent splashes.
In the event of a spill, hydraulic fluid creates a significant slip hazard and requires prompt cleanup due to its environmental impact. Used hydraulic fluid must be handled according to local environmental regulations, as improper disposal contaminates soil and water sources. General safety practice involves minimizing contact, ensuring good personal hygiene, and washing hands thoroughly after handling.