While biodegradable hydraulic fluids are safer for the environment and an excellent design choice, they do require specific design considerations due to their reaction with equipment components, seals and other materials.
Synthetics and vegetable oils have both been well documented in comparison to traditional mineral-oil-based lubricants. Suppliers have undertaken additional methods to ensure fluid compatibility since little information may be available. Industrial users of these products and their material suppliers know they have to treat biodegradable lubricants differently than standard mineral-based oils. In order to gain a better understanding of material and application compatibility, a good starting point begins with the review of the various lubricant considerations.
Biodegradable Lubricants: Compatibility, Conversion, Complications
Biodegradable lubricants are appropriate for use with equipment in many industries — essentially anywhere the lubricants may come into contact with the environment. Some examples are mining, oil & gas exploration and production, forestry, and maritime.
There are practical considerations related to making adjustments from mineral-based lubricants to biodegradable fluids that are often overlooked. These biodegradable lubricants often differ in their characteristics. The conversion necessary for their effective use is not quite as simple as draining the used mineral oil and pouring in the new biodegradable lubricant. Before converting to a biodegradable lubricant, it is imperative to consider the lubricating system’s operating and design characteristics. These factors include:
- The type of sealing or hose materials used;
- The potential for contamination, such as water, dust or dirt;
- Operating temperature, pressures and flow rates; and
- Whether or not the quality of the existing filtration system is sufficient for the new fluid.
One of the critical areas for consideration frequently overlooked is whether or not the new biodegradable fluid is compatible with mineral oil. If it is not, complications may occur if all of the old mineral oil is not thoroughly flushed from the system before the new fluid is installed.
There are many indicators of an inadequate or incomplete conversion to biodegradable fluids. This could encompass leaking seals, severe foaming, increased operating temperatures, plugged filters, and/or higher-than-normal wear on some components (such as the hydraulic pump).
Eco-friendly Vegetable Oils & The Supplier’s Impact
Soybean, corn, sunflower, rapeseed (canola), peanut, and olive oil are typical vegetable oils that translate to eco-friendly lubricants. In their natural form, these oils are comprised primarily of triglyceride molecular structures and therefore performance limitations such as poor thermal, hydrolytic and oxidative stability can pose problems. For instance, many natural vegetable oils cannot tolerate reservoir temperatures greater than 176 F (80 C).
It is often the case that the end-user specifies a biodegradable fluid for an application, leading component suppliers and their customers to produce an effective, compliant solution. In this scenario, suppliers need to collaborate with their customers to determine the best seal material for the fluid type specified. In addition to working with the customer, suppliers should also be working with fluid manufacturers to develop a mutual understanding of how seals behave in their fluids and vice versa. This proactive approach solves challenges on both ends of the supply chain. We find that fluid manufacturers want to understand how their fluid additives affect seals, and the topic of chemical compatibility often comes up. For some of these fluids, it is important to define the application, or failure could become a possibility should the customer or fluid manufacturer try to use the environmentally friendly hydraulic fluid the same way that they would use a mineral-based fluid.
It is very important that hydraulic fluids transfer power efficiently and economically. Fluids with poor lubricity characteristics can lead to such things as pump wear and eventually equipment failure. Excessive heat build-up due to poor lubrication will result in seal wear and could lead to a defective surface finish.
|A typical hydraulic cylinder (photo courtesy of Trelleborg Sealing Solutions)|
There are some key properties to review when evaluating environmentally friendly hydraulic fluids:
Viscosity: The viscosity index is a measure of the degree of change in the viscosity of a fluid as changes in temperature occur. The higher the viscosity index, the less the fluid thins when its temperature increases, and the less the fluid thickens when its temperature decreases. Suppliers need to evaluate the viscosity index as it factors in a hydraulic fluid’s performance, especially when there are wide fluctuations in the fluid’s temperature.
Compatibility: In system component compatibility along with the hydraulic fluid, the fluid needs to be relatively inert in its reaction to the materials of construction and must be compatible with the system’s seals and finishes. The fluid must be thermal and shear stable to resist breakdown from oxidation and bacteria while also being non-reactive with all system components.
Low/High Pressure: Low vapor pressure is important to prevent cavitation and high wear rates of the hydraulic pumps. High vapor pressures of some water-based hydraulic fluids result in significant cavitation problems.
Compressibility: Typically, the compressibility of fluids used for hydraulic purposes is insignificant at pressures up to 3,000 PSI. High compressibility results in lower efficiency and higher apparent viscosity characteristics. Low foaming properties are essential to efficient operation. Serious foaming problems can result in cavitation of the pumps and excessive wear.
Lubricity: Good lubricity increases in importance as the operating system pressure increases. Those systems that operate at pressures greater than a few hundred PSI (pounds per square inch) usually require incorporating anti-wear agents to reduce friction and wear.
Low Specific Gravity: The higher the specific gravity of the fluid, the lower the overall operating efficiency.
Non-Flammability (High Flash Point): With hydraulics, non-flammability is often an essential property of the fluid. Some applications require a specially designed fire-resistant fluid. Flammability is usually measured by flash and fire points.
High heat transfer capabilities: This is important to aid in removal of the heat generated in normal pumping and use of the hydraulic fluid.
Demulsibility: As a measure of oil’s ability to resist emulsification with water, for most systems, it is desirable that the hydraulic fluid resists emulsification and allows for the separation and removal of water.
Low Pour Point: A low pour point is vital for fluids used outdoors in cold climates. Pour point is a measure of the lowest temperature at which a fluid can be poured. Recommendations for pour points should be at least 10-20 F below the lowest actual operating temperature.
Oil & Gas Applications and Stress
One of the greatest applications for biodegradable fluids is in oil and gas exploration and production. Fluid suppliers have responded by introducing new, eco-friendly biodegradable and non-toxic fluids based on a variety of different chemistries. What is needed is not only a sealing solution that can handle the fluid, but also handle all the other demanding parts of that application, such as saltwater, storms, various tidal and freezing conditions. In critical operations, the hydraulics often have to operate 24 hours continuously. Any downtime is very costly. Seal manufacturers have responded to this trend by ensuring their seals are able to interact appropriately with these new greener fluids. Oil and gas exploration applications continue to be complicated due to economic pressures that are moving the industry toward higher operating pressures, temperatures, and working cycles, all of which are more efficient but also increase the stress on components such as seals and lubricants.
In addition, government regulations aimed at protecting the environment must be considered for those who design, build, or use hydraulic systems. With this in mind, it is important to understand the entire sealing system, use application engineers to gather customer requirements and evaluate the application. Specifically, a shoulder-to-shoulder design engineering approach where collaboration between the seal supplier and the customer’s application engineers makes a difference in delivering substantial added-value and a total value of ownership advantage.
There are a number of advantages to using biodegradable hydraulic fluid, but the most important factor is that it will prevent pollutants from contaminating the soil and ground water.
Seal suppliers to hydraulic equipment manufacturers must be knowledgeable with regard to chemical compatibility requirements. Working with material suppliers that understand these challenges and that are able to perform the proper testing to ensure compatibility is imperative for a smooth transition. In addition to compatibility, suppliers should also know how to extend advantages received with standard hydrocarbon-based fluids such as a longer operating life of the seal, lower friction and reduced energy consumption, enhanced sealing techniques, and the delivery of a total value of ownership.
Joe Savina is Fluid Power Application Engineer for Trelleborg Sealing Solutions. He specializes in seal design, mechanical engineering, and manufacturing for fluid power applications. He has worked for Trelleborg in various engineering positions for more than 17 years. Mr. Savina has degrees in Industrial Maintenance and Physics.