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THE PREMIUM PRICE OF SYNTHETICS MUST BE WEIGHED AGAINST LIFECYCLE COSTS AND HIGHER PERFORMANCE
Five years ago, mineral oils dominated the lube oil marketplace. Synthetics were considered too expensive for most applications and only used for aeroderivative turbines in specific niches.
Today mineral oils are still king. But synthetics are gaining ground in many applications, consistently outpacing the growth of competitors. This is especially true in the developed world, where more advanced machinery is used. Companies, such as, Shell, ExxonMobil, BP, Dupont, Dow Chemical, Royal Purple and others offer a wide range of synthetic products.
Propelled by the higher performance requirements of modern equipment, as well as increasingly stringent environmental standards, synthetics will expand their share of the overall lubricant market, according to The Fredonia Group, which predicts an annual growth of 8.6% per year to $7.4 billion by 2015 (Table).
But these figures include all types of synthetic oils including automotive engine oils which account for half the total. In the North American turbomachinery market, synthetics accounted for 27% of the total 43.4 million gallons, according the Kline Report “Opportunities in Lubricants 2008- 2010 North American Market.”
The biggest complaint about synthetics has always been cost. Most synthetics are three-to-five times the price of mineral oils, sometimes less depending on the type considered, according to Greg Livingstone, Executive Vice President, Fluitec. But the price differential between minerals and synthetics is closing. This is due to the rising price of minerals and the increased use of synthetics, which drives up demand while lowering prices.
The higher initial cost of synthetics can be justified in less-than-ideal or highly stressed operating conditions, said Lubrication and Reliability Engineer Heinz Bloch. Users can expect a four-to-six-fold longer drain interval than mineral oils, assuming the lubricant is kept clean. And synthetics generate less frictional heat than performance-equivalent mineral oils, and will typically perform in a much wider range of ambient environments (Figure 1).
For example, steam turbines in coal-fired and nuclear power plants use synthetic phosphate esters as electro-hydraulic control fluids for their fire-resistant properties. These fluids also are used in gas turbine applications, such as gas transmission or off-shore locations where turbine oil with high fire resistance is required.
Concerns remain, however, because the chemistry and properties of some synthetic oils are still being understood, said Livingstone. Today’s polyaklylene glycol (PAG) turbine oils are incompatible with mineral oil, so there is always concern when using this chemistry in equipment that has contained mineral oils in the past. Even though the plant may have gone through an exhaustive effort to flush the system, residual mineral oil often remains. There are also questions about the long-term effect of synthetics on paints and seals.
The benefits of PAGs should not be overlooked, however. The polar composition of PAG-based synthetic fluids produce low-molecular weight byproducts that do not agglomerate and form varnish or sludge, said Govind Khemchandani, Senior Technical Specialist, Dow Chemical (Figure 2). PAGs also reduce the potential for entrained air bubbles that can lead to microdieseling, have better electrical conductivity, and do not break down or react with water. This minimizes fluid degradation and acid formation that can damage equipment.
“Higher initial cost has to be viewed in the context of reduced down time and fewer turbine trips,” said Felix Guerzoni, Product Application Specialist for Industrial Lubricants, Shell Global Solutions. “Utilities are looking for longer oil life and trouble-free service, so synthetic-based lubricants are likely to gain wider use.”
Another reason synthetics are catching on is that operators are learning the value of synthetics in troubleshooting, added Guerzoni. Whenever operating parameters drift from their ideal range of conditions, serious consideration should be given to synthetics. Similarly, rapid payback can be achieved whenever synthetics are used in failure-prone equipment and critically important machinery, such as pumps where repeat failures have been experienced.
Synthetic lubricants have better demulsibility, air separation, viscometrics and loadcarrying than their hydrocarbon counterparts, said Bloch. As such, many are used in applications subject to contamination because they give extra assurance of lubrication even in the presence of water.
“Efforts to avoid repeat bearing failures in large process pumps place emphasis on well-formulated synthetic fluids,” he added. “These superior lubes should be used at the slightest hint of increased vibration excursions.”
Meanwhile, companies have developed a host of synthetic products for this highly competitive market:
• Shell Turbo GT 32 is used for bearing lubrication in heavy duty gas turbines and combined cycle power plants. It is also used in dynamic centrifugal and axial compressors and pumps
• Dow Chemical’s PAG-based synthetic turbine fluid meets the requirements of GE’s gas turbine lubricant recommendation document, GEK 32568h. It is said to increase reliability and efficiency and prevent varnish formation.
•Dupont Krytox lubricants have been used for over 20 years in power generation facilities due to their high-temperature stability, chemical inertness, low volatility and non-flammability. This includes turbine auxiliary systems on Siemens-Westinghouse, Mitsubishi and GE models, as well as maintenance applications, such as gear boxes, dampers, valves, gaskets and seals. These Group V PFPEs are said not to oxidize to form varnish or other deposits.
•ExxonMobil Chemical offers synthetics such as: Mobil DTE 732M for use in MHI non-geared single-shaft gas and steam turbines, and multi-shaft turbines; and Mobil DTE 932 GT for large frame turbines employing a common lube reservoir under severe operating conditions, such as the GE Frame 3, 5, 6, 7 and 9.
• BP supplies Enersyn RC-S, a range of PAO lubricants containing zinc-free antiwear additives, anti-oxidants, and anti-foam and corrosion inhibitors. Enersyn LPS-PO 68 is a PAO said to offer high-performance and low-pour point designed for a refrigeration compressor
• Royal Purple provides synthetics for compressors, such as Poly-Guard FDA, as well as SynFilm GT, a multi-purpose oil recommended for gas and steam turbines, blowers, vacuum pumps and bearings. It is said to work well when oil reservoir temperatures exceed 200°F.
To be sure, synthetics are not required in all turbomachinery applications. In hydro turbines and coal plants, for example, where turbine oils may be in service for 20 years or more, there is no major thermal stress on the oil, said Guerzoni. Mineral-based turbine oils have proven successful over the years.
Synthetics are not necessarily a panacea for all lubricant ills, said Livingstone. Having a high-performing, long-life lubricant depends on selecting the best oil for the application, having strong condition monitoring and contamination control programs, and a culture of good maintenance and reliability practice. “A formulation using a Group I base stock may work well in a steam turbine application,” he added, “but it would be a waste of money to upgrade to synthetics.”
Mineral oil producers, such as Petro- Canada and Lubrizol, claim that their products are more than adequate for most applications and less costly than synthetics. Petro- Canada manufactures TurboFlo oil-based turbine lubricants to address extreme conditions in steam and gas turbines.
“TurboFlo fluids are specifically designed to lubricate and cool steam and gas turbines and deliver excellent lubrication to bearings,” said Larry Curts, Product Specialist, Petro-Canada. They are blends of severely cracked base oils and additives.
Lubrizol also provides a wide selection of mineral oils. The company’s RO94HA has been optimized to provide good filterability, rust and corrosion protection, and water separation, said Kellie Work, Lubrizol’s Industrial Additives Product Manger.
In any case, as operators demand more power, efficiency and performance from turbomachinery, the demand for advanced materials will continue to increase. “It is important to determine the value of the product in service and balance the initial cost relative to lifecycle costs,” said Guerzoni.