In the early 1900’s, there were few reported cases of lubrication related failures in power generation turbines. In the 1920’s, oil quality was suspected in deposit tendencies. In the 1950s, oil oxidation problems were solved with just changing oil but it wasn’t until 1976 that General Electric reported the relationship between acid increase and how it was associated with deposit formation. Many power generation facilities were hydro power or fueled by coal. The problems pertaining to the reliability of the turbine oil system were based on maintaining an adequate oil supply to the system, reducing the influence of trapped air, and trouble free lubrication in cases of high oil temperature. The systems were dependent on a natural resource namely coal. While coal may have been plentiful, it still had to be mined and transported which was costly. There was a less expensive energy source – nuclear. In the 1970s, there was a major push to utilize nuclear energy which accounted for the majority of the energy produced but safety and nuclear waste concerns lost favor for other energy sources such as diesel and natural gas. Natural gas has always been a source of energy but it wasn’t until the mid-1990s that natural gas became the predominate source for energy fuel due to the advancement of hydraulic fracturing. In the beginning of 2000, natural gas became the major source of fuel to power turbines.
Lubricating oil for these power turbines also evolved with a shift in the base oil technology. Group I stock was used; it was inexpensive and it had a predictable, liner degradation path. In many instances, the turbine oil could last up to 10 to 15 years in service. When power generation units became more advanced, they produced a much more aggressive environment for turbine oils. The Group I technology was being challenged. Group II stock began being used which provided greater stability and less varnish generation due in part because of the reduced sulfur concentration that was been proven to contribute to acid generation and deposit build-up. Though Group II oils may create less varnish, the varnish created in Group I oils would stay in suspension more readily due to the better solvency properties. Group II base stock oils also have a higher viscosity index and when compounded with amine and phenolic anti-oxidant additives, are very stable over a much longer period of time and temperature fluctuations compared to Group I. This was advantageous to turbines with systems holding fifteen thousand gallons or more. Oil changes were expensive and the system required shut down. These new formulations resulted in higher performance and longevity but they still needed to be monitored and maintained. While a Group I base stock had a liner demise in performance, Group II base stocks maintained a high level but as soon as the life expectancy threshold was hit, the degradation path was exponential. Oil analysis became a must.
The new systems used sensitive controls and experienced increased thermal stress loads. The duty cycles changed requiring turbine oils to have increased functions. Varnish now became an influential issue. Varnish on thrust bearings, bearing sleeves, sludge in gas turbines, and on valve spools cost the power generation industry millions of dollars in down time every year. Turbine lubricant oil manufacturers have stepped up to the challenge by engineering oils to address these issues by providing anti-corrosion, anti-wear, anti-oxidant, anti-foaming technology in the overall goal to produce oils that provide protection and can stay in the system for over twenty years. When systems are optimum, reliability is within grasp but often there is a false sense of confidence in the oil technology. Oil breakdown is complex mostly due to the degradation process of the base oil combined with additive breakdown and contamination. The only way to truly understand if a problem is emerging is thorough turbine oil analysis.
The combination of selecting an excellent product, controlling contamination as well as a testing protocol to identify emerging issues is the best approach to achieve the highest possible opportunity to achieve the greatest level of equipment productivity. ALS Tribology offers a systematic approach to turbine oil analysis through monthly, quarterly, and an annual comprehensive analysis regime. Contact ALS Tribology to find out how your power generation turbines can achieve the highest level of productivity entitlement.
Michael D. Holloway MLT1, OMA1, MLA1, CLS
Manager – Strategic Accounts and External Training, Tribology