13.1 Traditional Types of Oil
Traditionally, oils are generally classified as Refined and Synthetic.
Paraffinic and Naphthenic oils are refined from crude oil, while Synthetic oils are manufactured, or processed, from crude oil. Long-chain molecules and ring structures are associated with paraffinic and naphthenic oils, respectively. These terms refer to the arrangement of hydrogen and carbon atoms that make up the molecular structure of the oils. Discussion of the chemical structure of oils is beyond the scope of this manual.
The distinguishing characteristics between these 3 types of Non-Renewable oils are noted below:
(1) Paraffinic Oils
Paraffinic oils are distinguished by a molecular structure composed of long chains of hydrocarbons, i.e., the hydrogen and carbon atoms are linked in a long linear series similar to a chain. Paraffinic oils contain 'Paraffin Wax' and are the most widely used Base Stock for lubricating oils.
In comparison with naphthenic oils, paraffinic oils have:
- Excellent Oxidation Stability (higher resistance to Oxidation)
- Higher Pour Point
- Higher Viscosity Index
- Low Volatility and, consequently, high Flash Points
- Low Specific Gravities
(2) Naphthenic Oils
In contrast to paraffinic oils, naphthenic oils are distinguished by a molecular structure composed of 'rings' of hydrocarbons, i.e., the hydrogen and carbon atoms are linked in a circular pattern. These oils do not contain wax and behave differently than paraffinic oils.
Naphthenic oils have:
- Good Stability
- Lower Pour Point due to Absence of Wax
- Lower Viscosity Indexes
- Higher Volatility and, consequently, low Flash Points
- Higher Specific Gravities
Naphthenic oils are generally reserved for applications with narrow temperature ranges and where a low Pour Point is required.
(3) Synthetic Oils
Synthetic lubricants are produced from chemical synthesis rather than from the refinement of existing petroleum or vegetable oils. These oils are generally superior to petroleum (mineral) lubricants in most circumstances.
Synthetic oils perform better than mineral oils in the following respects:
- Better Oxidation Stability or Resistance
- Better Viscosity Index
- Much lower Pour Point, As low as -46 °C (-50 °F)
- Lower Coefficient of Friction
The advantages offered by synthetic oils are most notable at either very low or very high temperatures. Good Oxidation Stability and a lower coefficient of friction permits operation at higher temperatures. The better Viscosity Index and lower pour points permit operation at lower temperatures.
The major disadvantage to synthetic oils is the initial cost, which is approximately three times higher than mineral-based oils. However, the initial premium is usually recovered over the life of the product, which is about three times longer than conventional lubricants. The higher cost makes it inadvisable to use synthetics in oil systems experiencing leakage.
Note: Synthetic oils are not necessarily interchangeable. It is important to note that synthetic oils are as different from each other as they are from mineral oils. Their performance and applicability to any specific situation depends on the Quality of the synthetic base oil and additive package.
Synthetic Lubricant Categories
Several major categories of synthetic lubricants are available including:
(1) Synthesized Hydrocarbons
Polyalphaolefins and dialkylated benzenes are the most common types. These lubricants provide performance characteristics closest to mineral oils and are compatible with them.
Applications include engine and turbine oils, hydraulic fluids, gear and bearing oils, and compressor oils.
(2) Organic Esters
Diabasic acid and polyol esters are the most common types. The properties of these oils are easily enhanced through additives. Applications include crankcase oils and compressor lubricants.
(3) Phosphate Esters
These oils are suited for fire-resistance applications.
Applications include gears, bearings, and compressors for hydrocarbon gases.
These oils are chemically inert, nontoxic, fire-resistant, and water repellant. They also have low pour points and volatility, good low-temperature fluidity, and good oxidation and thermal stability at high temperatures.
13.2 Nonfluid, Solid Lubrication
Definition of Solid Lubricant
A solid lubricant is a material used as powder or thin film to provide protection from damage during relative movement and to reduce friction and wear. Other terms commonly used for solid lubrication include dry lubrication, dry-film lubrication, and solid-film lubrication.
Although these terms imply that solid lubrication takes place under dry conditions, fluids are frequently used as a medium or as a lubricant with solid additives. Perhaps the most commonly used solid lubricants are the inorganic compounds Graphite and Molybdenum Disulfide (MoS).
Characteristics of Solid Lubrication
The properties important in determining the suitability of a material for use as a solid lubricant are discussed below.
a. Crystal Structure
Solid lubricants such as graphite and MoS possess a lamellar crystal structure with an inherently low shear strength. Although the lamellar structure is very favorable for materials such as lubricants, nonlamellar materials also provide satisfactory lubrication.
b. Thermal Stability
Thermal stability is very important since one of the most significant uses for solid lubricants is in high temperature applications not tolerated by other lubricants. Good thermal stability ensures that the solid lubricant will not undergo undesirable phase or structural changes at high or low temperature extremes.
c. Oxidation Stability
The lubricant should not undergo undesirable Oxidation changes when used within the applicable temperature range.
The lubricant should have a low vapor pressure for the expected application at extreme temperatures and in low-pressure conditions.
e. Chemical Reactivity
The lubricant should form a strong, adherent film on the base material.
The life of solid films can only be maintained if the film remains intact. Mobility of adsorbates on the surfaces promotes self-healing and prolongs the endurance of films.
g. Melting point
If the melting point is exceeded, the atomic bonds that maintain the molecular structure are destroyed, rendering the lubricant ineffective.
Some materials with suitable characteristics, such as those already noted, have failed as solid lubricants because of excessive hardness. A maximum hardness of 5 on the Mohs' scale appears to be the practical limit for solid lubricants.
i. Electrical Conductivity
Certain applications, such as sliding electric contacts, require high electrical conductivity while other applications, such as insulators making rubbing contact, require low conductivity.
Solid Lubricant Applications
Generally, solid lubricants are used in applications not tolerated by more conventional lubricants. The most common conditions requiring use of solid lubricants are discussed below.
(1) Extreme Temperature And Pressure Conditions
These are defined as high-temperature applications up to 1926 °C ( 3500 °F), where other lubricants are prone to degradation or decomposition; extremely low temperatures, down to -212 °C (-350 °F), where lubricants may solidify or congeal; and high-to-full- vacuum applications, such as space, where lubricants may volatilize.
(2) As Additives
Graphite, MoS, and zinc oxide are frequently added to fluids and greases. Surface conversion coatings are often used to supplement other lubricants.
(3) Intermittent Loading Conditions
When equipment is stored or is idle for prolonged periods, solids provide permanent, noncorrosive lubrication.
(4) Inaccessible Locations
Where access for servicing is especially difficult, solid lubricants offer a distinct advantage, provided the lubricant is satisfactory for the intended loads and speeds.
(5) High Dust And Lint Areas
Solids are also useful in areas where fluids may tend to pick up dust and lint with liquid lubricants; these contaminants more readily form a grinding paste, causing damage to equipment.
Because of their solid consistency, solids may be used in applications where the lubricant must not migrate to other locations and cause contamination of other equipment, parts, or products.
Solid lubricants are effective in applications where the lubricated equipment is immersed in water that may be polluted by other lubricants, such as oils and greases.
Advantages of Solid Lubricants
- More effective than fluid lubricants at high loads and speeds.
- High resistance to deterioration in storage.
- Highly stable in extreme temperature, pressure, radiation, and reactive environments.
- Permit equipment to be lighter and simpler because lubrication distribution systems and seals are not required.
Disadvantages of Solid Lubricants
- Poor self-healing properties. A broken solid film tends to shorten the useful life of the lubricant.
- Poor heat dissipation. This condition is especially true with polymers due to their low thermal conductivities.
- Higher coefficient of friction and wear than hydrodynamically lubricated bearings.
- Color associated with solids may be undesirable.
Types of Solid Lubricants
The most common materials are Graphite and Molybdenum Disulfide.
Graphite has a low friction coefficient and very high thermal stability (2000 EC [3632 EF] and above). However, practical application is limited to a range of 500 to 600 °C (932 to 1112 °F) due to oxidation. Furthermore, because graphite relies on adsorbed moisture or vapors to achieve low friction, use may be further limited. At temperatures as low as 100 °C (212 °F), the amount of water vapor adsorbed may be significantly reduced to the point that low friction cannot be maintained. In some instances sufficient vapors may be extracted from contaminants in the surrounding environment or may be deliberately introduced to maintain low friction.
When necessary, additives composed of inorganic compounds may be added to enable use at temperatures to 550 °C ( 1022 °F). Another concern is that graphite promotes electrolysis. Graphite has a very noble potential of + 0.25V, which can lead to severe galvanic corrosion of copper alloys and stainless steels in saline waters.
(2) Molybdenum Disulfide (MoS)
Like graphite, MoS has a low friction coefficient, but, unlike graphite, it does not rely on adsorbed vapors or moisture. In fact, adsorbed vapors may actually result in a slight, but insignificant, increase in friction.
MoS also has greater load-carrying capacity and its manufacturing quality is better controlled. Thermal stability in non-oxidizing environments is acceptable to 1100 °C (2012 °F), but in air it may be reduced to a range of 350 to 400 °C (662 to 752 °F).
Dispersions of Powdered Solids
Dispersions are mixtures of solid lubricant in grease or fluid lubricants. The most common solids used are Graphite and Molybdenum Disulfide (MoS). The grease or fluid provides normal lubrication while the solid lubricant increases lubricity and provides extreme pressure protection.
Addition of MoS to lubricating oils can increase load-carrying capacity, reduce wear, and increase life in roller bearings, and has also been found to reduce wear and friction in automotive applications.
Note: Caution must be exercised when using these solids with greases and lubricating fluids:
- Grease and oil may prevent good adhesion of the solid to the protected surface.
- Detergent additives in some oils can also inhibit the wear-reducing ability of MoS and graphite, and some antiwear additives may actually increase wear.
- Solid lubricants can also affect the Oxidation Stability of oils and greases. Consequently, the concentration of Oxidation Inhibitors required must be carefully examined and controlled.
13.3 Environmentally Acceptable (EA) Lubricants
Mineral Oil based lubricating oils, greases, and hydraulic fluids are found in widespread use throughout industry. However, these products are usually toxic and not readily biodegradable.
Because of these hazardous characteristics, if these materials escape to the environment, the impacts tend to be cumulative and consequently harmful to plant, fish, and wildlife. Due to these potential hazards, the Environmental Protection Agency (EPA) and other government regulators have imposed increasingly stringent regulations on the use, containment, and disposal of these materials. For instance, the EPA requires that no visible oil sheen be evident downstream from facilities located in or close to waterways. Another regulation requires that point discharges into waterways should not exceed 10 parts per million (ppm) of mineral-based oils.
Facilities such as Hydropower Plants, Flood-Control Pumping Plants, and Lock-And-Dam Sites either are or have the potential to become polluters due to the use of mineral-oil-based materials in these facilities. Grease, Hydraulic Fluids, and Oil leaking from equipment may be carried into the waterway.
Because of the difficulty in completely eliminating spills and discharges of these mineral-oil- based materials, and to alleviate concerns about their impact on the environment, a new class of Environmentally Acceptable (EA) lubricants was created intended for use in sensitive locations.
EA lubricants, as contrasted to Mineral Oil and Synthetic based equivalents, are nontoxic and decompose into water and carbon dioxide (CO).
Since the creation the EA catagory, a new category has emerged showing all the promises of being Renewable, Sustainable, Recyclable, and Biodegradable along with very High Quality Performance features, namely Stabilized High Oleic Base Stocks.
13.3.1 Definition of EA Lubricants
The lubrication industry uses a variety of terms to address 'Environmental' lubricants. A few of these terms, all preceded by the term Environmentally, are: acceptable, aware, benign, friendly, harmless, safe, sensitive, and suitable. Two other commonly used terms are Green Fluids and Food Grade lubricants. The term green fluid is mostly used for lubricants manufactured from vegetable oil. Food grade lubricants are rated by the U.S. Department of Agriculture (USDA) and generally are used in the food industry where incidental food contact may occur. Food grade lubricants may or may not qualify as EA lubricants. Indeed, most food grade lubricants are made of U.S.P. White Mineral Oil which is not toxic but does not meet the biodegradability criteria commonly required of EA lubricants.
Environmentally Acceptable, or "EA", is a commonly used term and is used by some ASTM committees to address environmental lubricants.
Note: This manual does not use the term Environmentally Acceptable, or EA. It is discussed for purpose of reference. In this manual, EA applies to petroluem-based oils, fluids, and greases. EA lubricants may be rated Readily biodegradeable, however, they are made from Non-Renewable crude oils.
The EA category is useful in distinquishing High Oleic Base Stocks, (HOBS), which are rated Ultimate Biodegradation by the U.S.D.A., from petroleum based offerings advertising "Bio" in their labels, meaning Biodegradability - not Biobased.
Note: This manual refers to the terms Renewable, Biobased, or Bio when discussing Oils, Greases, and Fluids made from High Oleic Base Stocks, (HOBS).
At the present time there are no standards for EA lubricants or hydraulic fluids. Manufacturers and end users agree that for a lubricant to be classified as an EA type it should be biodegradable and nontoxic. This means that if a small quantity of EA fluid is inadvertently spilled into the environment, such as a waterway, it should readily break down and not cause harm to fish, plants, or wildlife.
U.S. standards-writing organizations are currently working to develop nationally recognized tests and procedures for demonstrating compliance with various environmental criteria such as biodegradability and toxicity. The ASTM Committee on Petroleum Products and Lubricants has formed a subcommittee, referred to as the Subcommittee on Environmental Standards for Lubricants, which is tasked with developing test methods for determining aerobic aquatic biodegradation and aquatic toxicity of lubricants.
The methodology developed by this subcommittee, ASTM D 5864, for determining the aerobic aquatic biodegradation of the lubricants, was accepted for standard use by the ASTM in December 1995. The subcommittee is also developing a test method for determining the aquatic toxicity of lubricants. With approval of these standards, it is expected that these methods will be used by industry for evaluating and specifying EA fluids.
Note: Lacking formally approved U.S. test procedures, suppliers of EA lubricants frequently use established European standards to demonstrate their products' compliance with U.S. criteria. In this manual, references are made to these European standards.
The Base Fluids discussed herein may be used for preparation of Hydraulic Fluids, Lubrication Oils, or Greases.
Biodegradation is defined as the chemical breakdown or transformation of a substance caused by organisms or their enzymes.
(2) Primary Biodegradation
Primary Biodegradation is defined as a modification of a substance by microorganisms that causes a change in some measurable property of the substance.
(3) Readily Biodegradable
Readily Biodegradable. 60 percent or more of the test material carbon must be converted to CO in 28 days.
(4) Ultimate Biodegradation
Ultimate Biodegradation is the degradation achieved when a substance is totally utilized by microorganisms resulting in the production of carbon dioxide, methane, water, mineral salts, and new microbial cellular constituents.
Each of United Bio Lube's 160 Biobased Lubricants in 30 categories are rated Biobased and Ultimate Biodegradation by the U.S. Department of Agriculture (USDA) and Worker Friendly by the Occupational Safety & Health Administration (OSHA).
For a complete discussion of Biobased and Biodegradation, see 'Chapter 6 - Understanding Biobased and Biodegradable'.
Test method ASTM D 5864 determines lubricant biodegradation. This test determines the rate and extent of Aerobic Aquatic Biodegradation of lubricants when exposed to an Inoculum under laboratory conditions. The inoculum may be the activated sewage-sludge from a domestic sewage-treatment plant, or it may be derived from soil or natural surface waters, or any combination of the three sources.
The degree of biodegradability is measured by calculating the rate of conversion of the lubricant to CO. A lubricant, hydraulic fluid, or grease is classified as Readily Biodegradable when 60 percent or more of the test material carbon is converted to CO in 28 days, as determined using this test method.
The most established test methods used by the lubricant industry for evaluating the biodegradability of their products are Method CEC-L-33-A-94 developed by the Coordinating European Council (CEC); Method OECD 301B, Modified Sturm Test, developed by the Organization for Economic Cooperation and Development (OECD); and Method EPA 560/6-82-003, No. CG-2000, Shake Flask Test, adapted by the U.S. Environmental Protection Agency (EPA).
These tests also determine the rate and extent of Aerobic Aquatic Biodegradation under laboratory conditions. The Modified Sturm Test and Shake Flask Test also calculate the rate of conversion of the lubricant to CO . The CEC2 test measures the disappearance of the lubricant by analyzing test material at various incubation times through infrared spectroscopy. Laboratory tests have shown that the degradation rates may vary widely among the various test methods indicated above.
Toxicity of a substance is generally evaluated by conducting an acute toxicity test. While awaiting acceptance of the ASTM test method for determining the aquatic toxicity of lubricants, the most common test methods used by the lubricant industry for evaluating the acute toxicity of their products are EPA 560/6-82-002, Sections EG-9 and ES-6, and OECD 203. These tests determine the concentration of a substance that produces a toxic effect on a specified percentage of test organisms in 96 hours. The acute toxicity test is normally conducted using rainbow trout.
Toxicity is expressed as concentration in parts per million (ppm) of the test material that results in a 50 percent mortality rate after 96 hours (LC50). A substance is generally considered acceptable if aquatic toxicity (LC50) exceeds 1000 ppm. That is, a lubricant or a hydraulic fluid is generally considered acceptable if a concentration of greater than 1000 ppm of the material in an aqueous solution is needed to achieve a 50 percent mortality rate in the test organism.
13.3.4 EA Base Fluids and Additives
Base Fluids are mixed with additives to form the final products. These additives are necessary because they provide the resulting end product with physical and chemical characteristics such as Oxidation Stability, foaming, etc., required for successful application.
Note: Most additives currently used for mineral based oil are toxic and non-biodegradable. Therefore, they cannot be used with EA fluids. Furthermore, since the physical and chemical properties of EA fluids are quite different than those of mineral oil, EA fluids will require entirely different additives.
Additives that are more than 80 percent biodegradable (CEC-L33-T82) are available. Several additive manufacturers are working with the lubricant industry to produce environmentally suitable additives for improving the properties of EA base fluids.
Sulfurized fatty materials (animal fat or vegetable oils) are used to formulate Extreme Pressure/Anti-Wear additives, and Succinic Acid Derivatives are used to produce Ashless (no metal) additives for corrosion protection.
Suppliers are using a variety of base fluids to formulate EA hydraulic fluids, lubricating oils, and greases. The base fluid may be the same for all three products.
For example a biodegradable and nontoxic ester may be used as the base fluid for production of hydraulic fluid, lubricating oil, and grease.
The most popular Base Fluids are Non-Stabilized Vegetable Oils, Synthetic Esters, and Polyglycols:
Non-Stabilized Vegetable Oils
Vegetable oil production reaches the billions of gallons in the United States. However, due to technical complexity and economic reasons, few are usable for formulating EA fluids. The usable Non-Stabilized Vegetable Oils offer excellent lubricating properties, and they are nontoxic and highly biodegradable, relatively inexpensive compared to synthetic fluids, and are made from natural renewable resources.
Conversion to vegetable-oil-based fluids should present few problems, as all are mixable with mineral oil. However, contamination with mineral oil should be kept to a minimum so that biodegradability will not be affected.
Special filter elements are not required. Filters should be checked after 50 hours of operation, as vegetable oils tend to remove mineral-oil deposits from the system and carry these to the filters. Filter-clogging indicators should be carefully monitored, as filter-element service life may be reduced in comparison to mineral-oil operation.
Rapeseed Oil (RO)
In the Bio Lubricants Industry, Rapeseed Oil (RO), or Canola Oil, appears to be the 'Base Oil' of choice for the most popular of the Biodegradable Hydraulic Fluids in the market. The first RO-based hydraulic fluids were commercially available in 1985.
Laboratory tests have identified limits to the use of this oil, but extensive practical experience has yielded relatively few problems. The quality of RO has improved over time, and it has become increasingly popular, but it has problems at both high and low temperatures and tends to age rapidly. Its cost, about double that of mineral oil, still makes it more affordable than many alternative EA fluids.
The benefits of RO include its plentiful supply, excellent lubricity, and high Viscosity Index and flash point. RO is highly biodegradable. One popular RO achieves its maximum biodegradation after only 9 days. RO possesses good extreme pressure and antiwear properties, and readily passes the Vickers 35VQ25 vane pump wear tests. It offers good corrosion protection for hydraulic systems and does not attack seal materials, varnish, or paint. Mixing with mineral oil is acceptable and has no influence on oil performance. RO is not water soluble and is lighter than water. Escaped oil can be skimmed off the surface of water. Molecular weight is high, indicating low volatility and low evaporation loss.
Concerns about RO include poor low-temperature fluidity and rapid oxidation at high temperatures. Vegetable oil lubricants, including rapeseed, castor, and sunflower oils, tend to age quickly. At high temperatures, they become dense and change composition; at low temperatures, they thicken and gel. Some RO products are not recommended for use in ambient temperatures above 32 °C (90 °F) or below -6EC (21 °F), but other products gel only after extended periods below -18 °C (0 °F) and will perform well up to 82EC (180 °F).
The major problem with RO is its high content of Linoleic and Linolenic fatty acids. These acids are characterized by two and three double bonds, respectively. A greater number of these bonds in the product results in a material more sensitive to and prone to rapid oxidation.
Traditionally, these problems have been only partially controlled by anti-oxidants. Refining the base oil to reduce these acids results in increased stability. Testing indicates that vegetable oils with Higher Oleic' content have increased Oxidation Stability.
Stabilized High Oleic Base Stocks: Soy, Corn, Canola, and Sunflower Oils
Today, Hybrid Breeding and Genetic Engineering have produced Soy, Corn, Canola, and Sunflower Oils with very high concentrations of Oleic Acid for industrial and military applications requiring better Oxidation Stability, Thermal Stability, and Load Carrying Capacity.
With the advent of Stabilized technology, High Oleic Base Stocks, i.e. Soy, Corn, Canola, and Sunflower Oils, are now functional lubricants at extreme temperatures while meeting, or exceeding, physical performance properties and qualities of mineral oils and synthetic lubricants.
United Bio Lube has over 160 Biobased Lubricants in 30 categories based on Stabilized HOBS technology. No other competitor to date has duplicated the levels of performance of Stabilized HOBS technology. 3rd party testing demostrates HOBS OUTPERFORMS competitive petroleum based products.
Renewable, Sustainable, Recyclable, and Biodegradable, HOBS are setting new performance, safety, and environmental standards across industries.
See Chapter 7 - High Oleic Base Stocks, (HOBS) for a detailed discussion on the properties, testing, and featues of HOBS.
Synthetic Esters (SE)
Synthetic Esters have been in use longer than any other synthetic-based fluid. They were originally used as aircraft jet engine lubricants in the 1950s and still are used as the base fluid for almost all aircraft jet engine lubricants. For EA base lubricants, the most commonly used Synthetic Esters are polyol esters; the most commonly used polyol esters are trimethylolpropane and pentaerithritol.
Synthetic Esters are made from modified animal fat and vegetable oil reacted with alcohol. While there are similarities between RO and SEs, there are important differences. Esters are more thermally stable and have much higher Oxidation stability.
SE fluids can be regarded as one of the best Biodegradable hydraulic fluids. Synthetic Esters with suitable additives can also be nontoxic. They perform well as lubricants. They have excellent lubrication properties: high Viscosity Index and low friction characteristics. Their liquidity at low and high temperatures is excellent, as is their aging stability.
Although they mix well with mineral oils, this characteristic negatively influences their biodegradability. SE fluids offer good corrosion protection and lubricity and usually can be used under the same operating conditions as mineral oils. They are applicable for extreme temperature-range operations.
Synthetic Esters do have higher first cost and are incompatible with some paints, finishes, and some seal materials. However, it may be possible to extend Oil change intervals and partially offset the higher cost.
Since SE fluids are miscible with mineral oil, conversion may be accomplished by flushing the system to reduce the residual mineral-oil content to a minimum. Special filter elements are not required.
Filters should be checked after 50 hours of operation, as vegetable oil tends to remove mineral-oil deposits from the system and carry them to the filters.
The use of Polyglycols is declining due to their aquatic toxicity when mixed with lubricating additives and their incompatibility with mineral oils and seal materials.
Polyglycol hydraulic fluids have been available for several decades and are widely used, particularly in the food-processing industry. They also have been used since the mid-1980 in construction machinery (primarily excavators) and a variety of stationary installations. They were the first biodegradable oils on the market.
PG fluids have the greatest stability with a range from -45 to 250 °C (-49 to 482 °F). Polyglycols excel where fire hazard is a concern. Oil change intervals are similar to those for a mineral oil: 2000 hours or once a year.
PG oils are not compatible with mineral oils and may not be compatible with common coatings, linings, seals, and gasket materials. They must be stored in containers free of linings. Some PG oils do not biodegrade well. The rate and degree of biodegradation are controlled by the ratio of propylene to ethylene oxides, with polyethylene glycols being the more biodegradable. The rate and extent of biodegradability diminish with increasing molecular weight.
13.3.5 Properties of Available EA Products
Disposal costs for EA oils may be greater than for mineral oils because recyclers will not accept them. As previously noted, laboratory tests have shown that the degradation rates may vary widely among the various biodegradation test methods.
Both Vegetable Oil and Synthetic Ester based fluids, if formulated properly, are Readily Biodegradable. The toxicity tests show that the base stocks of most EA lubricants are nontoxic. The wide range of toxicity is caused by additives in the formulated products.
The following discussion summarizes important properties of EA fluids.
a. Oxidation Stability
One of the most important properties of lubricating oils and hydraulic fluids is Oxidation Stability. Oils with low values of Oxidation Stability will oxidize rapidly in the presence of water at elevated temperatures. When oil oxidizes it will undergo a complex chemical reaction that will produce acid and sludge. Sludge may settle in critical areas of the equipment and interfere with the lubrication and cooling functions of the fluid. The oxidized oil will also corrode the equipment.
Oxidation Stability is normally measured by test method ASTM D 943. This test, which is commonly known as Turbine Oil Stability Test (TOST), is used to evaluate the Oxidation Stability of oils in the presence of oxygen, water, and iron-copper catalyst at an elevated temperature.
Lubricity is the degree to which an oil or grease lubricates moving parts and minimizes wear. Lubricity is usually measured by Test Method ASTM D 2266, commonly known as the Four-Ball Method. Laboratory tests have shown that EA lubricants normally produce good wear properties.
c. Pour Point
Pour Point defines the temperature at which an oil solidifies. When oil solidifies, its performance is greatly compromised. Pour Point is normally evaluated by test method ASTM D 97. The low-temperature fluidity of Non-Stabilized Vegetable Oil based fluids is poor compared to Stabilized HOBS fluids.
Note: The Pour Point of Non-Stabilized Vegetable Oils based hydraulic fluids and lubricants may be acceptable for many applications.
d. Viscosity Index
Viscosity Index (VI) is a measure of the variation in the kinematic viscosity of oils as the temperature changes. The higher the Viscosity Index, the less the effect of temperature on its kinematic viscosity. VI is measured by test method ASTM D 2270. The VI of most EA fluids meets or exceeds the VI of petroleum based fluids.
The tendency of oils to foam can be a serious problem in lubricating and hydraulic systems. The lubrication and hydraulic properties of oils are greatly impeded by excessive foaming. Foaming characteristics of oils are usually determined by test method ASTM D 892. Laboratory tests have shown that most formulated EA fluids do not have foaming problems.
f. Paint Compatibility
Some common paints used in fluid systems are incompatible with many EA fluids. When it is anticipated that EA fluids may be used in a fluid system, the use of epoxy resin paints should be used to eliminate potential compatibility problems.
g. Elastomeric Seal Compatibility
Polyurethane seals should not be used with EA fluids. Instead, the use of Viton and Buna N (low to medium nitrile) is recommended. EA fluids are compatible with steel and copper alloys and provide excellent rust protection. The fluid manufacturer must be consulted for specific compatibility data for each material encountered in the application.
Since EA fluids are biodegradable they will break down in the presence of water and bacteria. Moisture traps in breather intakes and other equipment modifications which will keep moisture out of the system should be considered. EA fluids should be periodically monitored to insure that biodegradation is not occurring.
13.3.6 Environmentally Acceptable Guidelines
At present there are no industry or guide specifications for EA fluids and greases.
Until specific standards and specifications are developed, it is recommended that the following guidance be used for qualifying the fluids to be environmentally acceptable:
(1) They must be Non-Toxic
That is, using test method EPA 560/6-82-002, concentrations greater than 1000 ppm of the test material are necessary to kill 50 percent of the test organisms in 96 hours (LC50>1000).
(2) They must be Readily Biodegradable
That is, using the ASTM Test Method D 5864, 60 percent or more of the test material carbon must be converted to CO in 28 days.
13.3.7 Changing from Conventional to EA Lubricants
Original Equipment Manufacturers (OEMs), Plant Operators considering a change to Biodegradable lubricants and hydraulic fluids should, above all, be aware that these products are not identical to conventional mineral oil products. Furthermore, the EA fluids are not necessarily equal to one another. It is important to make a thorough assessment of the requirements of the specific application to determine whether a substitution can be made, and whether any compromises in quality or performance will be compatible with the needs of the user.
Switching to EA - products may require special considerations, measures, or adaptations to the system.
Depending on the application and the product chosen, these could include the following:
- Some commercially available synthetic ester and vegetable-oil-based lubricants meet the requirements of nontoxicity and biodegradability.
Note: The compatibility of these fluids with existing materials encountered in the application, such as paints, filters, and seals, must be considered.
The fluid manufacturer must be consulted for specific compatibility data for each material of construction. The manufacturer of the existing equipment must be consulted, especially when the equipment is still under warranty.
- Extreme care must be taken when selecting an EA oil or grease for an application. Product availability may be impacted due to the dynamic nature of developing standards and environmental requirements. EA lubricating oils should not be used in hydroelectric turbine applications, such as bearing oil, runner hub oil, or governor oil, until extensive tests are performed.
- Accelerated fluid degradation at high temperature, change of performance characteristics at low temperature, and possible new filtration requirements should be investigated carefully. The oxidation rate of vegetable-based EA lubricants increases markedly above 82 °C (179.6 °F), and lengthy exposure at the low temperature can cause some products to gel.
- On a hydraulic power system, when changing over to EA lubricants, the system should be thoroughly drained of the mineral oil and, if possible, flushed. Flushing is mandatory if diesel engine oil was the previous hydraulic fluid. This will avoid compromising the biodegradability and low toxicity of the EA fluids. Disposal of the used fluids should be in accordance with applicable environmental regulations and procedures.
- More frequent filter changes may be necesary.
- Moisture scavengers may be necessary on breather intakes to keep water content in the lubricant low.
- Temperature controls for both upper and lower extremes may need to be added to the system.
- Redesign of hydraulic systems to include larger reservoirs may be necessary to deal with foaming problems.
- The use of stainless steel components to protect against corrosion may be necessary.