Lubrication: Industry Leaders Look to Fix the Varnish Issue

Issue 2 and Volume 112.

By David Wagman, Managing Editor

Power Engineering magazine invited leaders at top lubrication companies to take part in a wide-ranging “state of the industry” discussion. Those taking part included John Sewell, chief engineering manager, Northeast Region, Exxon Lubricants and Specialties; Gene Finner, lubrication specialist, Applications Engineering Technical Service, Dow Corning Molykote; Kevin P. Kovanda, president, American Chemical Technologies Inc.; Jeff Turner, executive vice president, Lubrication Engineers Inc.; and Felix Guerzoni, product application specialist, Shell Lubricants.

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Power Engineering (PE): What are the primary advantages of synthetic oil over conventional oil in electric power generation applications?

Lubrication Engineers: Synthetic products are well-suited for use in applications where temperature extremes are experienced. For example, in an area of a power plant where poor ventilation results in extremely high temperatures, a synthetic-based product may be necessary to provide increased oxidation stability.

Dow Corning Molykote: In electric power generation and distribution, high voltage circuit breakers and disconnect switches are expected to remain in service for up to 20 years without major service. The temperature inside a circuit breaker may range from 140 F to -40 F over the course of a year with wide daily fluctuations based on night and day during the same season. When compounded with environmental extremes such as severe cold, extreme heat, wind, water and airborne contamination, conventional mineral oil-based lubricants are often unable to measure up.

In this industry, synthetic lubricants such as silicone- and polyalphaolefin- (PAO-) based lubricants provide longer service life due to their inherent ability to resist changes in viscosity and drying out. For example, in needle bearings used in trip latch mechanisms, fluorosilicone grease has been demonstrated to provide many years of successful service without drying out. Mineral oil-based lubricants are more prone to drying out when exposed to high temperatures due to their increased volatility compared to the more thermally stable synthetics. Mineral oils also tend to have low viscosity indexes. They tend to thicken quickly as temperature decreases and thin quickly when temperature increases. In the case of a trip coil bearing, use of the wrong lubricant in colder conditions may mean the difference between an acceptable trip versus a delayed or failed trip. Over time, mineral-oil based grease may also dry out enough to prevent a successful trip.

The engineered properties of synthetics stand up in a wide range of applications to eliminate seasonal lubricant change-outs. Synthetics are widely used by original equipment manufacturers as life lubricants. Most high-voltage equipment today is constructed without grease ports, making it very difficult to re-lubricate unless it is brought into the shop and disassembled. Because of this, maintenance personnel should use synthetic lubricants to take advantage of longer service life and better performance at temperature extremes.

American Chemical Technologies: A great deal of concern is being heard in the industry over control and servo failures due to buildup of varnish/sludge deposits. Not just any synthetic will resolve this issue, but polyalkylene glycol (PAG) oils are particularly well suited toward the elimination of varnish induced control failures. PAG and other synthetics reduce the need for constant fluid monitoring and greatly lengthen change intervals. PAG fluids have been in continuous service in turbo compressors since 1997 (over 80,000 hours) without being changed and are still in the first half of fluid life, by analysis.

Exxon Lubricants and Specialties: Most big cogeneration plants average 40,000 to 50,000 hours on overhauls. The primary advantage of synthetic products is that they offer a longer drain interval. On gas turbine generator sets, synthetics are used extensively. Synthetics have greater thermal stability, exhibit less deposit formation and enjoy longer turbine oil life. There can also be a 1 percent to 3 percent energy savings, due to the traction coefficient of the oil. Synthetics require less energy to drive the machinery. Also, most synthetics can be recycled, allowing them to be used again and again.

Shell Lubricants: Synthetic biodegradable hydraulic oils offer oil life and performance equivalent to, if not superior to, that of conventional mineral oils with the additional benefit of reduced environmental impact, possessing high levels of biodegradability and low ecotoxicity. Such products can find application in hydro electric power stations.

Phosphate ester EHC fluids for steam turbines provide benefits of high fire resistance, low flammability and self-extinguishing properties. In the event of a rupture of a hydraulic hose on a steam turbine, there is less possibility of fire should the highly pressurized oil come into contact with hot metal surfaces. Such fluids are increasingly finding use as circulating fluids for gas turbines as a means of reducing fire risk in power generation facilities. In some cases, use of such products may lead to reductions in the operators overall insurance premiums.

In applications where the operating temperatures may be high, synthetic oils and greases offer a number of benefits: the high viscosity index (VI) leads to effective fluid film formation over the application temperature range and also better oxidation stability to resist the formation of sludges and deposits, which may extend not only oil life but component lifetime, with added benefit of reduced downtime and waste oil management costs.

Varnished spools out of a control valve. Vanish is a major concern for power-gen turbines. Photo courtesy Shell Lubricants.
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PE: What are the primary disadvantages that synthetic oil presents?

American Chemical Technologies: The only disadvantage is the first cost.

Shell Lubricants: Any change should first consider the operating system and the impact the use of a synthetic may have. With some synthetic oils, such as phosphate ester control fluids used in steam turbine EHC systems or ester-based synthetic compressor oils, some care needs to be taken to ensure compatibility with the components in the lubrication systems such as elastomers/seals, paints, filter media and other service oils.

Dow Corning Molykote: The initial cost of synthetic lubricants can be much higher but is offset over the life of use and in figuring total cost of ownership of lubricant and equipment. Some synthetics can cause problems with certain seals and gaskets and paints. Your lubricant supplier can provide information about this.

Exxon Lubricants and Specialties: The upfront cost can be the biggest disadvantage. Owners can see three to five times the initial cost of synthetics over mineral products. In part that’s because PAO involves an extra manufacturing cost. There’s also a lot of competition for the materials, which can be used in other high-value products. And if the product is applied in a location with leaks, then the owner probably will not realize the full benefits inherent in synthetics. The PAO-based synthetic may not be compatible with mineral oils already in the system. An operator may need to flush and clean a system before adding the synthetic.

Lubrication Engineers: The term “synthetic oil” is generally used to insinuate a lubricant formulated using either highly refined mineral oil or PAO-based lubricants. There are actually many more synthetic base fluids which can be used to formulate synthetic lubricants. Second, the cost of synthetic fluids is often much higher than conventional mineral oil products. One must decide if the extra price of the synthetic product actually delivers the value perceived by the user. Finally, for the PAO and highly refined mineral oil synthetics, additive and contaminant solubility can be issues. These products do not possess the natural ability to hold additives or manage contaminants that mineral oils do. They must be properly formulated by incorporating co-solubility additives, which then increases the price even more.

PE: What sort of cost differential may operators find by switching to synthetic oil?

Dow Corning Molykote: Quality synthetic compressor oils may cost more money when purchased compared to conventional oils. However, this up-front cost is generally recovered through long-term cost savings by reducing the overall amount of oil consumed and purchased, lowering the frequency of service calls, reducing downtime from frequent oil changes and lowering costs associated with waste oil disposal.

An average utility owns thousands of breakers and often has the resources to service only 40 to 50 of them each year. Due to the cost of the equipment and possible fines over CMI, the investment in long-life synthetics can save significant money in the long run.

Shell Lubricants: The cost differential compared to mineral oil varies by product. Shell recommends upgrading to synthetics in applications where the benefits of using the synthetic product outweigh the cost. Benefits can include longer drain intervals, lower system maintenance and reduced waste oil removal costs and component replacement.

Lubrication Engineers: The operators should probably expect to see an initial price increase of three to six times. Keep in mind, though, this may not be a true reflection the product cost. Cost of use is actually based upon product performance, longevity and reduced waste disposal. Do not fall into the trap of comparing the sale price when considering a cost differential.

American Chemical Technologies: The total costs should be greatly reduced by savings in maintenance, unplanned outages, loss of reliability, labor, and fluid changes. Considering those, price is somewhat more.

PE: Many power plants are working to extend the length of time between outages. What specific challenges does this strategy pose to lubrication?

Lubrication Engineers: In order for a power plant to extend its outage time, personnel are also assuming they can extend the time the lubricant can be used. Some might assume that a synthetic lubricant might last longer than a conventional lubricant. Based upon equipment used, environmental contamination and other maintenance practices, this may or may not be true. Recent attention has been given to problems with turbine oil sludge and varnish formation, which results from the use of certain lubricants in certain turbines. The challenge is to catch and solve these problems before they occur.

Dow Corning Molykote: With conventional oils, attempting to extend the time between outages risks lubricant degradation or failure, which can lead to costly equipment damage.

Power plant lubrication poses unique challenges: equipment is difficult to service in the field and the environmental conditions are extremely harsh. As a result, lubricants need to last as long as possible by not drying out or thickening to the point that they interfere with movement of components. A breaker should be lubricated with the idea to prevent wear, prevent corrosion and avoid seizure. Mechanical components do not move very often so failure from wear is often not the primary threat.

Shell Lubricants: One challenge is to ensure that the oil can withstand the extended drain intervals and performance extremes to which the oil is exposed. Oil life extension should be managed with a detailed oil condition monitoring program to allow for predictive and proactive maintenance. The oil analysis program should be designed in partnership with the customer and the supplier and be based on equipment criticality, expected oil drain intervals and a clear understanding of which tests to include and the frequency at which such tests should be conducted.

American Chemical Technologies: Since you can’t easily change on the fly, a need to change fluid can mean a plant shutdown or delay of change with possible other consequences. With PAG synthetic fluids, change intervals may be measured in decades, easily eliminating unplanned/unscheduled outages.

Exxon Mobil Lubrication: On the gas turbine side, the biggest issue is varnish and deposit issues on servo valves. When the turbines go into a short shutdown period, they can have problems with misfires and startup. Varnish is an industry-wide problem that extends to more than just the oil. As a result, the varnish problem won’t be solved solely by switching to synthetic oil.

PE: What major lubrication technology breakthrough did your company achieve during 2007 with regard to lubricants used in electric power generation?

Dow Corning Molykote: Although we brought no new lubricant technology to the industry in 2007 we have done a very good job of increasing understanding of lubricants, especially in how they can prevent corrosion when properly applied.

American Chemical Technologies: The first installation of PAG lubricants in a gas turbine power plant. This is a breakthrough because even though PAG fluids are well proven in other industries, a very conservative industry took the first step into a new lubricant paradigm.

Lubrication Engineers: In 2007 our company launched a major upgrade to our industrial gear oil line. This upgrade included improvements in thermal stability, foaming, shear stability and water separation. All of these improvements have now been shown to provide increased reliability in all types of bearing and gear applications. Also, we completed a study into the formulation of our mainline turbine oils. Based upon field performance, we see that they provide improved sludge and varnish resistance properties, as well as reduced foam formation and oil consumption.

Shell Lubricants: Shell Corena AS are PAO based compressor oils for rotary flooded screw compressors. The new technology in Shell Corena AS may allow the oil life to be extended to up to 12,000 hours even in severe running compressors operating in severe environments with high discharge temperatures and pressures, especially when used in combination with oil analysis.

PE: What major technology challenge is your company currently attempting to address, again with regard to electric power generation applications?

Shell Lubricants: Varnish has been a significant issue in recent years for turbine applications. Our new Shell Turbo Oil CC for gas and steam turbines, which will be introduced this year, is designed to provide even better protection against varnish and other oxidation by-products than our current formulation. Where synthetic lubricants are concerned, Shell is continuing development on energy efficient lubricants for major applications such as gearboxes and hydraulic systems.

Dow Corning Molykote: We are currently evaluating the long-term ability of lubricants to resist drying out by evaporation and bleed, in addition to examining the cold weather effects of various lubricants on delayed trip times. We also continue to seek a better lubricant for the jaw ends of horizontal disconnect switches.

Exxon Mobil Lubrication: We are working with OEMs to extend and overcome varnish in gas turbine and cogeneration applications. It’s a puzzle involving OEMs, operators and lubrication manufacturers, each having a piece to deal with.

Lubrication Engineers: We are focusing on how lubricant formulation plays a role in the reduction of oil consumption and in the formation of varnish and sludge in turbines. We feel that it plays a large role and also believe that we have found the answer to the question of how to formulate around these problems. The challenge lies in producing the lab test data that simulates what occurs during field performance. Turbine OEMs, lubricant additive manufacturers and lubricant producers have all been working together to create tests that will evaluate a finished lubricant’s ability to withstand the thermal degradation properties that form varnish and sludge. Although advanced knowledge has been gained in this area, the solution to this challenge has yet to be fully realized.