In addition to being subject to tough environmental standards, tight budgets, and penalties for supply interruptions, today’s power companies must ensure efficient and reliable operations to keep up with high demand. This means that power-generating turbines often run under more intense conditions than ever, including 24/7 cycles and frequent stopping and starting. Modern steam turbine oils must be able to handle less downtime, higher loads and temperatures, and longer oil drain intervals if they are to be of any effective use. Here’s how steam turbine oils can be selected and used efficiently under demanding operational conditions.
Maintenance and plant managers can optimize equipment efficiency and cut costs by selecting a steam turbine oil that serves several important functions. First, it must be able to lubricate all bearings, gears, flexible couplings, hydraulic controls, and oil shaft seals. Second, it must be able to resist high temperatures and provide effective cooling. And third, it should prevent corrosion, sludge, and rust while the turbine is spinning. Maintenance professionals can ensure that these performance criteria are met by monitoring several of the oil’s qualities, including its viscosity and viscosity index, demulsibility, rust and corrosion prevention, foam resistance, and oxidation stability.
Proper viscosity is what allows oil to efficiently reduce friction between moving parts, making it the most important quality to look for in a steam turbine oil. The size and output of a given piece of equipment will determine its required oil viscosity, with smaller turbines needing lower viscosities and larger turbines needing higher. An oil’s viscosity index, which shows how changes in temperature can affect overall viscosity, is also important. A higher viscosity index indicates that an oil is more likely to maintain its velocity under drastic temperature changes.
Hydro-electric and steam turbines are especially susceptible to water contamination, which can degrade oil and corrode parts. An effective turbine oil will thus have good demulsibility, which is the ability to separate from and resist water. Demulsibility can be measured by mixing 40 milliliters of distilled water with the same amount of turbine oil, stirring for five minutes at 54 degrees Celsius. This emulsion should separate to 3 ml of emulsion remaining within 15 minutes.
An effective turbine oil will also need to prevent both rust formation and chemical corrosion. This is achieved through oil additives that attach themselves to metal surfaces and protect them from both metallic oxide formations (rust) and attacks from strong acids and bases (corrosion). It should be noted that excessive amounts of rust and corrosion inhibitors can interfere with other critical oil additives, so it’s important to achieve a balanced formula.
A small amount of foam in turbine oil is normal and can generally be permitted. Excessive amounts of foam in oil, however, can overflow and contaminate the whole circulating system, causing damage to pumps, bearings, or other parts and systems. Properly formulated oil will have an adequate amount of anti-foam additives that should help to eliminate excess foam and air.
While it’s stored in the machine’s reservoir, the oil in a steam turbine is exposed to oxygen over long periods of time. This can lead to oxidation, which drastically diminishes the oil’s effectiveness. It’s therefore critical that maintenance and plant managers select a turbine oil with high oxidation resistance, especially in the presence of high temperatures and metallic contaminants, which can speed up the oxidation process.
Since 1978, Petrotech has been providing reliable and innovative control systems to businesses all along the global energy production pipeline. To learn more about our control system solutions for everything from advanced steam turbine controls to single valve fuel gas system retrofits, explore our whitepapers.