Part 2: Performance Aspects of U.S. EPA-Approved EALs
By James Burton
Vegetable Oils - Natural Triglycerides (HETG)
These products are usually made from either canola or soybean oils, and are readily biodegradable and very low in toxicity. Vegetable oils (along with animal fats) are the oldest and the original types of lubricants used by man and throughout history. They were used to lubricate chariot and carriage wheels, as well as a variety of other moving parts before crude oil was discovered. Vegetable-based oils are often given preference over other types of EALs by environmentalists and other supporters of the “green movement” for being considered as renewable resources since they are derived from harvested crops and not potentially exhaustible or limited sources, such as crude oil.
One of the considerations for promoting vegetable oil products to be used as EALs is that they are considered a “sustainable resource,” as are bio-based synthetic esters. However, bio-based synthetic esters require far more base material to manufacture the end product. The question becomes, then: Does this become an efficient use of sustainable crops? Recently, the idea of raising crops to produce base products in order to manufacture fuel and lubricants have come under fire from the same factions that initially promoted the use on “renewable resources and sustainability.” Some people are now stating that all available farmland should be used to feed the world’s growing population and not be used to manufacture fuel and lubricants for machinery. The subject of sustainability seems to also have its share of controversial issues with obviously opposing views on the allocation of crops and farmland for industrial use.
From a practical standpoint, vegetable oils can appear to have very good lubricity, but when temperature is increased, this is where they fall short on performance. Vegetable oils have poor thermal and oxidative stability. They can oxidize very rapidly at higher temperatures normally tolerated by mineral or synthetic oils, leading to varnish and solid deposits, thus offering a very short fluid life span, which is often considered unacceptable. The ASTM standard for oxidative stability (“TOST”) is often as low as 500 hours, compared to mineral oil with a rating of between 1,500 and 5,000 hours. When it comes to cold weather performance, most vegetable oils do not perform well, as they cannot operate in low temperatures such as in areas of the U.S. Midwest, Alaska, and much of Canada. While some products show excellent viscosity indexes, pour points are not conducive to these types of climates.
Another problem associated with vegetable oils is what is referred to as “hydrolytic stability,” which is the reactive nature of the product when it comes in contact with water. Vegetable oils react quite readily in the presence of moisture and water, leading to the formation of excessive acids and sludge. These acids can be very corrosive on components and seals, and can soften hydraulic hoses, leading to premature blowouts. The other issue with vegetable oils is that they can turn rancid and cause terrible odors in the process. This became evident in 2006 when vegetable oil-based hydraulic oil was installed in many elevators located in some of New York City’s subway stations. It very literally caused quite a stink with NYC’s transit users.
Converting a system to vegetable oil usually consists of draining and purging the system of the old fluid and filling it with the vegetable oil to be used. The system is then cycled for several hours to remove any traces of mineral or deleterious oil left in the system, drained, and finally refilled with the new vegetable oil. This is a necessary process, as any old fluid left in the system will compromise the integrity and biodegradability of the new oil. All flush oil must be disposed of, which can lead to some costly equipment conversion procedures, since it basically doubles the cost for the initial fill.
Likely the primary reason why these products are used to the extent that they are is partly due to apparent reasonable costs and the fact that these are the only type of biodegradable oils that most people are familiar with. Most people are not aware that there are other types of biodegradable oils and lubricants available in the lubricants marketplace.
From a marine compliance standpoint, vegetable oils may be U.S. EPA-approved EALs, but nevertheless they are still oil, and spills to water will fetch a fine for violating the Clean Water Act of 1990 and 40 CFR 435.
Synthetic Esters (HEES)
Synthetic esters are man-made lubricants developed from bio-based, plant esters and offer a significant improvement in overall performance over vegetable oils. These performance improvements include improved oxidation and thermal stability, viscosity index, and better lubricity at elevated temperatures. Synthetic esters often provide an oxidation stability life to over 10,000 hours, but most are closer to that of conventional mineral oil. Some synthetic esters are also rated as “fire resistant” by Factory Mutual and are frequently used in the steel and smelting industry. Because of the cost to produce synthetic ester-based lubricants, these products can be the most expensive EALs on the market, with some European-manufactured products costing over $60 per U.S. gallon. Many of the biodegradable oils or EALs offered in the marketplace are actually a blend of vegetable oils and synthetic esters, offering some of the performance advantages of the synthetic esters and the lower cost of the vegetable oil.
Some synthetic esters can offer pour points as low as -50 and viscosity indexes of over 200, and are suitable for cold temperature operations not available from standard vegetable oil. Along with better pour points, synthetic esters offer higher flash points and improved thermal stability over vegetable oils, which give the products a much longer fluid life span, reducing maintenance costs by offering far longer fluid drain intervals and thus offsetting the higher cost of the product. Both vegetable oils and synthetic esters offer excellent lubricity, but the synthetic esters provide superior lubrication at elevated temperatures and provide better overall system protection.
The downside to bio-based synthetic esters is that while they offer better thermal stability than vegetable oils, they are still prone to oxidation and varnish at elevated temperatures. Even synthesized hydrocarbons (inorganic or inorganic-based), such as PAOs, as well as synthetic esters have their upper limits for heat tolerance and will oxidize to form varnish over time. These synthetic oils will resist oxidation and the formation of solid deposits better than conventional mineral and vegetable oil, but with elevated pressures and heat over time, these products will also deteriorate if pushed past their useful capabilities. These products tend to be “non-polar” fluids, but the byproducts of decomposition formed by oxidation become high molecular weight polar molecules, which do not stay in solution and are attracted to the surfaces of the hydraulic system or gearbox. The result is that the oxidation byproducts of the fluid will build up on the inside of the system to create “varnish.”
Another “Achilles Heel” of vegetable oils, synthetic esters, as well as even mineral oils, is the chemical reaction with moisture and water, referred to as “hydrolyzing.” This chemical reaction over time can produce gumming and acids that, in turn, attach and soften seals and hoses, leading to leaks and ruptures, as well as promoting metal component corrosion. These gummy deposits, along with varnish buildup, can clog and render various valves and other components unusable, resulting in extensive overhauls of the system. In order to prevent system issues and failures, these products require fairly constant fluid sampling to be sure they are not pushed past their usable lifespan.
Because of the improved performance over vegetable oils, these products appear to be the ideal EAL as they offer superior lubrication, thermal, and oxidative resistance to conventional vegetable oils. For marine use, however, synthetic esters are in a very moist environment and may not fare well, and they may have a greater tendency to hydrolyze, as water and moisture are impossible to avoid. The maximum amount of water ingression tolerable by most oils (mineral or synthetic) is 200 ppm. Exceeding this will render the products unusable.
The fact that these products are considered “oil soluble” is usually considered an advantage of synthetic esters and bio-based PAOs over products such as water-soluble PAG fluid. Comments are often made in favor of these oil-based products as popular belief has it that conversions to these EALs are simpler, and that conventional oil can be used for top up if necessary. That may sound attractive in theory, but in reality, it is a major disadvantage.
When converting to an EAL, it is imperative that ALL the old oil be removed from the system so as not to jeopardize the integrity and biodegradability of the new fluid. After draining the entire system, it is then charged with new fluid and cycled for several hours, drained again to remove any residual old fluid, and then refilled a second time with new fluid. This process basically doubles the cost of an initial conversion required by these products.
The other issue is that if topping up the fluid with conventional oil either by accident or if the EAL fluid is unavailable, the EAL fluid will lose its environmentally friendly properties and subsequent compliant nature, making it necessary to replace the fluid in the entire system.
Another major disadvantage of these fluids is the tendency for these products to hydrolyze and create gum and corrosive acids as described in previous paragraphs, as well as the issue of environmental compliance and the Clean Water Act of 1990 and 40 CFR 435—the “no-sheen” rule.
Synthetic esters and bio-based PAO fluids may still be U.S. EPA-approved EALs, but nevertheless they are still oil. Oil and water do not mix, especially in a marine environment. Spills of any oil to water anywhere in the USA, regardless of the fact that it may or may not be an EPA-approved EAL, will still fetch a fine for violating the Clean Water Act of 1990 and 40 CFR 435. In Canada, Transport Canada views any oil (petroleum or otherwise) as potentially threatening to aquatic wildlife and can also (and have previously in the past) issue fines for polluting Canadian waterways under the Canada Shipping ACT in the event of spills of such products. We have to remember why we are converting to an approved EAL in the first place, and environment compliance should appear near the top of the list.
Polyalkylene Glycol (PAGs) (HEPG)
Polyalkylene glycol fluids are approved by the U.S. EPA as acceptable EALs due to both the rate of biodegradability and low aquatic toxicity. Although these products are not “bio” in nature, as they are derived from natural gas, products such as Dow UCON Trident AW 32, for instance, is rated at 81% biodegradable in 28 days (OECD 301F). As previously mentioned, the U.S. EPA’s guideline calls for a minimum of 60% biodegradable in 28 days and must meet stringent aquatic toxicity requirements. The U.S. EPA classifies this product as “practically non-toxic,” whereas Transport Canada considers it “non-toxic.”
Polyalkylene glycol lubricants are rather unique when compared to other synthetic lubricants, such as synthetic hydrocarbons or synthetic vegetable esters. These polymers can be designed and tailored to achieve certain characteristics or capabilities in order to perform very specific functions or performance requirements to suit the application. Polyalkylene glycol lubricants can be described as “designed,” not refined.
PAG Applications and Benefits
Because of the properties that make up PAG lubricants, they are uniquely suited for a number of industrial and manufacturing applications. Their water solubility allows for easy cleanup of equipment. PAG lubricants offer high viscosity indexes and are shear stable. PAGs are also valued for their low volatility in high-temperature applications, and for resistance to formation of residue and deposits. Their biodegradability makes them ideal for environmentally sensitive applications.1
While these water-soluble PAG fluids have similar biodegradability ratings to synthetic esters, they also have one major advantage over all other EALs that are oil based. Water-soluble PAG fluids are not classified as “oil” by the U.S. Coast Guard and are not considered “oil” by Transport Canada. These PAG fluids will not form a visible slick or sheen on the surface of the water (unlike any oil-based product) since these products are not oil or oil with added emulsifiers. They are not only heavier than water with a typical specific gravity of about 1.03, but also dissolve readily when mixed with water. Since these products completely dissolve and dissipate when discharged into water, they do not form an oil slick that can contaminate wildlife or foul shorelines and contaminate marshes. As the fluids dissolve and continue to dissipate, the environmental impact is continuously being reduced by the action of the currents, waves, and tides. The slick itself, regardless of the toxicity or biodegradability of the oil in the event of a spill, accounts for much of the initial mortality in marine wildlife in the initial stages of the discharge. One of the reasons the U.S. EPA enacted the Clean Water Act of 1990 and the Non-Sheen Regulation 40 CFR 435 was to try to reduce the environmental impact of any type of free oil floating in the surface of the water.
These water-soluble PAG fluids not only have a far lighter impact on the environment if spilled into water, but also offer additional environmental compliance not offered by any of the oil-based U.S. EPA EALs. Spills of water-soluble PAGs will not violate the U.S. EPA’s Clean Water Act of 1990 and the Non-Sheen Regulation 40 CFR 435. In Canada, these water-soluble PAG lubricants are not classified as marine pollutants by Transport Canada under the “Pollution from Ships” section of the Canada Shipping ACT. The majority of fines for oil spills to water in the U.S. are for violating the Clean Water Act and 40 CFR 435. If the fluid is neither a hazardous chemical and is not considered oil, it is exempt from this act, as well as OPA 90 oil spill cleanup regulations. This will not only reduce or eliminate fines, but can also dramatically reduce the scope and costs associated with aquatic oil spill cleanup procedures and remediation. After all, if you convert your marine-based equipment to an approved EAL, doesn’t it make sense that it not only provides a lighter environmental impact, as well as a level of compliance, but also prevent costly fines, cleanup and remediation procedures?
Polyalkylene glycols, especially water-soluble PAGs, are too often overlooked as viable EALs. The petroleum and lubricant industry often dismisses these products because they are not compatible with other conventional oils and not produced by major refiners. Many people confuse these fluids with water glycol fluids (water glycol fluids can have up to 45% water content), but products such as UCON Trident AW, EnBio Industry’s EnBio TCS, and American Chemicals Technology’s Neptune (including EP and XP) lubricants are anhydrous, or contain no water. PAG fluids have already solved high heat and varnish issues in applications such as compressor fluids, where even PAOs were failing due to the severe heat and friction in high RPM compressors. The main reason for this reluctance of acceptance is lack of knowledge of PAG fluids and unfamiliarity of the major differences in both environmental, compliance reasons, and performance advantages with these fluids.
Water-soluble PAG fluids are not compatible with conventional oil, which is often the objection to using them, but that is not really an issue at all. If mixed with conventional oil, the water-soluble PAG fluids will completely separate from the oil, and the oil can be easily isolated. This is actually a huge advantage over oil-soluble EALs since adding conventional hydraulic oil to an EAL will compromise the integrity of the fluid in the entire system and defeat the purpose of using a readily biodegradable fluid. I have heard that some equipment operators make statements such as, “If we are in a remote location, we need something that is compatible with what oil is available.” If they are in an area or location that requires the use of an approved EAL, adding conventional oil is not an option if you wish to remain compliant. The other issue is that many equipment operators are concerned only about having the equipment operational, and planning ahead may not be part of their job requirement or concern. Environmental compliance often entails a bit of management strategy, such as have extra EAL fluid available at the remote job site to remain compliant in the event of a spill.
The fact that water-soluble PAG fluids do not mix with oil is also a major advantage when converting the system to an EAL. To convert a hydraulic system to a conventional EAL, the system has to be drained and purged, then cycled for a few hours with the new EAL product to remove all residue of the old oil, drained, and finally refilled with the new fluid. All the flush material must be disposed, as it is contaminated with the old, non-biodegradable fluid. This process virtually doubles the initial cost of the first installation.
To convert to a water-soluble PAG EAL, the same draining, purging, and flushing process is repeated, however, all the fluid used to flush the system is not discarded. It will readily and completely separate from the conventional oil, the oil can be skimmed off, and the PAG fluid can be reused. This can cut the cost of an initial conversion to almost half.
Consider the fact that in a marine environment, spills of any oil can be a violation, so why not remove oil out of the equation altogether? Why fight fire with fire when water-soluble PAG fluids are not only U.S. EPA-approved EALs, but also the only EALs that do not violate the Clean Water Act of 1990 and Non-Sheen Rule 40 CFR 435? In Canada, even vegetable oil can be classified as marine pollutants if it can contaminate any marine wildlife. Transport Canada does not classify PAGs as marine pollutants under the pollution from ships section of the Canada Shipping Act. It is very simple: oil and water do not mix, and oil is the enemy in a marine environment, so why rely on EALs for marine use that could be considered a marine pollutant?
The performance advantages of using a PAG-type EAL fluid versus either synthetic esters or vegetable oils is very evident in basically all areas of evaluating lubricants. One of the major reasons why many equipment managers are reluctant to convert equipment to an approved EAL is a perceived reduced fluid life span, increased maintenance, and reduced equipment performance.
In terms of lubricating ability, PAG fluids produce less friction than even other synthetic fluids, such as synthetic esters or PAOs. Rexroth noted in the test section of its approval letter for UCON Trident AW the test results from the Southwest Research Institute: Since UCON™ TRIDENT™ was shown, by Southwest Research Institute, to give less wear than mineral oil in the Vickers 35VQ Test, we tested this fluid at a load pressure of 5,000 psi (345) bar in a Rexroth A4VSO125 axial piston pump at 1450 rpm. Although this pressure is higher than the 4,600-psi pressure specified for a HFD (synthetic, fire-resistant, water-free) type fluid [1], the Vickers 35VQ results suggest that this fluid may have better anti-wear properties than conventional hydraulic mineral oils.
The following is a summary of the test parameters2: (Fig. 2)
Load carrying ability: Many water–soluble PAG hydraulic fluids pass all 12 stages of the FZG visual gear test, and some PAG gear fluids, such as ACT’s Neptune EP and XP gear lubricants, have doubled the Timken load and increased the load wear index by over 35% when compared to even PAO gear oils. PAG gear fluids maintain much higher viscosities at high temperatures (100°C) than their conventional and synthetic counterparts.
Superior oxidative stability: PAG hydraulic and gear fluids offer superior oxidation resistance when compared to any other type of synthetic or conventional lubricants (Fig. 1). Not only do PAG fluids resist oxidation, adding to a much longer fluid life, but they are also incapable of forming solid deposits, such as varnish or coking. This is partly because the molecular structure of the PAG is fully saturated, but it is a polar fluid to begin with, and when the fluid eventually starts to oxidize, the byproducts of oxidation are also polar by nature, and therefore stay in solution. Conventional and synthetic oils are non-polar by nature, but produce polar byproducts, which results in the buildup of varnish in a system when subjected to excessive amounts of heat and pressure for too long a period of time (Fig. 3).
Superior thermal stability: PAG fluids can withstand temperature spikes up to 250°F without compromising the integrity of the fluid. This is one reason why PAGs have been used in high-heat applications, such as high RPM industrial compressors and as fire-resistant hydraulic fluids. PAG fluids can tolerate heat that would readily create varnish and even coking in other fluids, including PAOs and synthetic esters.
Material compatibility: Numerous past articles written about PAG fluids note that a downside to PAGs is seal and material compatibility. This may have been an issue in the past, and there may be some compressor fluids that are picky about seal materials, but rotary screw and centrifugal-type compressors can generate much higher temperatures than hydraulic systems. The fluids used in these applications require much different formulations and additives than those used as hydraulic fluid and have different seal compatibility. Products such as UCON Trident or ACT’s Neptune gear fluids have good seal compatibility and can be used with most common seal materials, such as Buna, Viton, Neoprene, Kalrez, and many others, so installing new seals throughout the system is rarely required. As far as coatings or paint is concerned, it is recommended that either two-part epoxy or no coating at all be used, as PAG fluids will lift oil-based alkyd paints. Lufkin Industries suggest two-part epoxy be used over alkyd paints on all their gearboxes for any synthetic fluids used in its equipment.
Viscosity range: One complaint with vegetable-based oils is cold weather capabilities and pour points that are not conducive for use in northern climates such as Alaska, the Canadian prairies, or northern U.S. Plains. UCON Trident AW 32, for example, has a viscosity index of about 200 and pour points of -51°C, as well as a viscosity of 8.0cst @ 100°C3, compared to a typical AW 32 with a pour point of about -33°C and viscosity of 5.4cst @100°C (based upon a VI of 95). This viscosity range makes these products (AW 32, 46, or 68) suitable for basically any climate or operating conditions.
Since the presence of water in hydrocarbon-based fluids or vegetable and synthetic esters would be problematic due to the chemical reactions (hydrolyzing), as well as hydrogen embrittlement, it is assumed by many people that it also creates issues with PAG fluids. While PAG fluids that are not soluble in water will absorb 0.07% water, and water-soluble PAGs will absorb 100% water, it is not an issue at all as PAGs are practically inert to the presence of water. PAG fluids have a very minimal or negligible reaction to the presence of moisture or water, so corrosive acids and gums are not produced, nor does hydrogen embrittlement become an issue, as they would be with hydrocarbons and especially vegetable oils and vegetable esters. The intolerance to water and formation of gum and acids, along with other negative reactions from the presence of moisture, are some of the major problems associated with both bio-based and petroleum oil products. The other advantage to the water-soluble PAG fluids in a marine environment is that they will handle up to 1.5% water contamination (15,000 ppm) before the performance begins to diminish. There is no saturation point as there is with conventional hydrocarbons (maximum saturation point of most mineral oils is 200 ppm), but viscosity and lubricity will slowly be reduced as the water content is increased. PAG fluids also offer excellent corrosion protection if affected by water; after all, water glycol hydraulic fluids used in the steel and smelting industry contain up to 45% water. In the event of severe water contamination of the hydraulic system or gearbox, water can be extracted from these PAG fluids with a vacuum dehydrator and the fluid simply put back into service.
Contrary to popular belief, most OEMS generally do not list “approved” types of fluid, but rather set minimum performance standards that the lubricant must meet or exceed to satisfy warranty requirements. For hydraulic or gear fluids this usually means meeting the performance requirements of a typical AW 32 or 46 hydraulic fluid or a typical EP-type gear lubricants of a specified viscosity. Unfortunately due to the fact that the use of these EALs is a relatively recent trend, many OEMs are not familiar with or have little experience with EALs, and can only relate to the performance and experience of using conventional lubricants in their products.
Conclusion
As mentioned previously, an article was written and published in the July 2012 issue of STLE’s TLT magazine called “In search of the Perfect EAL,” and the comment was “It doesn’t exist.” Since petroleum and oil-based products are the accepted norm in the lubricants industry, the mindset has been these are the “only” lubricants to be taken seriously.
Disadvantages often pointed out in regards to these water-soluble PAG fluids are in reality an advantage, such as the water solubility and the fact that they do not mix with oil. This can actually save a lot of time and money. A common mistake is made when hydraulic oil is accidentally added to the water-soluble PAG reservoir. This oil can be removed as it floats on top and lowers the cost of conversions, since the fluids separate and the oil can be skimmed off for removal, allowing the PAG fluid to be reused. If an oil-based fluid is contaminated with conventional oil, either caused by maintenance errors or the result of a flush from a conversion, the contaminated material must be disposed of, adding to either compromised product or more costly conversions.
Polyalkylene glycol fluids reduce or eliminate many of the other issues created by conventional EALs, such as shorter fluid life and increased maintenance intervals. This is the main reason many equipment managers avoid using EALs as they are viewed as costly, inferior lubricants that require much more maintenance and bring their own set of problems. Some U.S. equipment managers have stated, ”We use a biodegradable oil, and we still get a fine when we spill it in the water. What is the point in converting our equipment if we are still going to get fined?” Spills of any type of oil, regardless of the nature of the product, will likely result in fines and costly cleanup procedures. Wouldn’t it make sense to avoid using oil-based lubricants in applications such as “oil-to-sea interfaces” in the first place if there are viable alternatives?
Water-soluble PAGs are often said to be very costly, but are actually less expensive to purchase than many of the synthetic esters or PAO synthetics on the market, especially those of European origin, and offer much more in both performance and value. They can outperform conventional and synthetic oil when it comes to friction, thermal stability, oxidation stability, and solid deposits while avoiding acid formation in the presence of water, and they are able to handle much more water contamination than conventional oil-based lubricants. These products provide much longer fluid life than other types of lubricants, resulting in much lower overall operating costs. If you also consider the lighter environmental impact and higher level of compliance, reduced liabilities, and cleanup costs offered with these products, it is basically a win-win-win situation.
To sum it up, if water–soluble PAG fluids are not the perfect biodegradable lubricant, or EAL, they come as close as anything that has been developed to date.
For more information: James Burton has been involved in the lubricants and environmental compliance field for over 30 years. He is the technical representative for Coast Lubricants, a company covering the Pacific Northwest supplying biodegradable and other high-performance industrial lubricants. He can be reached at jamesburton@shaw.ca.
Acknowledgments:
(1): Daryl Beatty, Martin Greaves, Dow Chemical; “PAGs are rising to the top of the synthetic market”
(2): Bosch Rexroth Corp.
(3): Dow Chemical; UCON Lubricants
(4): American Chemical Technologies Inc.