Assessing oxidation condition and lubricant refreshment in turbine oils
March 2023Maintenance, Test & Measurement, Calibration
In turbines, lubrication undergoes a hydrodynamic regimen in which wear arises only after very poor lubricant condition. Conversely, the main root cause of turbine failure is the formation of deposits. Deposits produce several detrimental effects on these systems, such as sticking valves, orifice obstruction, and inefficient heat exchange.
In the case of gas turbines, where the lubricant suffers mainly from thermal stress, deposits are usually associated with the formation of varnish. Varnish is commonly associated with oxidation processes. It is composed of sacrificed antioxidants and oxidation products that coalesce to form sticky soft matter. The cost of varnish is very high, both in downtime and in equipment replacement. For this reason, monitoring of the oxidation condition of turbine oils is of utter importance.
To protect the base oil from oxidation, turbine lubricants are supplemented with about 1% of antioxidants. These are sacrificed to protect the base oil from free radicals and thermal and oxidative stress.
It is usually accepted that turbine oils can be used until their remaining active antioxidants are 25% of the original formulation. In many cases, however, depending on the oil, varnish issues arise before this point. Both laboratory tests and turbine oil condition monitoring, show that varnish may start to build up even when remaining antioxidants are as high as 60%.
In order to keep the operation reliable, the oxidation condition of a turbine must be kept between safe boundaries. This implies keeping a high dose of antioxidants, and the varnish potential low, to predict a high oxidation resistance.
Oil refreshment is a viable option to keep turbines free of varnish. By integrating the outcomes of lubricant analytics, such as RULER (Remaining Useful Life Evaluation Routine), RPVOT (Rotating Pressure Vessel Oxidation Test), and MPC (Membrane Patch Colorimetry), it is possible to estimate the refreshment required to keep the turbine under lean operation.
The lubricant’s oxidation condition can be effectively monitored through RULER, MPC, and RPVOT tests. Besides the nominal ASTM (American Society for Testing and Materials) value for these tests, significant information can be gathered from digging into these tests and integrating their outcomes.
One major application for this integration is the estimation of the lubricant refreshment for lean operation. Through laboratory tests, this can be accurately estimated, planning ahead of the upcoming maintenance intervention. This method is shown, together with case studies.
WearCheck team celebrates diagnostic milestone Wearcheck
Motion Control & Drives
Condition monitoring specialist company, WearCheck celebrated a noteworthy milestone recently when diagnostic manager, John Evans diagnosed his three millionth used oil sample at the company’s Durban laboratory.
Read more...WearCheck leads the way in condition monitoring Wearcheck
Maintenance, Test & Measurement, Calibration
Minimising maintenance costs of mining and power-generating machinery and maximising its operational efficiency – these goals form the foundation of the proactive/preventive maintenance services provided by the expert technicians at condition monitoring specialist, WearCheck.
Read more...Collect data three times faster SKF South Africa
Maintenance, Test & Measurement, Calibration
SKF has extended its renowned Microlog Analyzer family of data collection devices with the addition of the Microlog Analyzer dBX. Currently SKF’s most powerful diagnostic tool, this cutting-edge device redefines diagnostic capabilities, enabling users to take measurements three times faster than its predecessor.
Read more...WearCheck Water assesses water quality Wearcheck
News
WearCheck Water, a division of condition monitoring specialist, WearCheck provides deep insight into the composition of water from multiple sources in a broad range of industries.
Read more...Integrated liners for the mining industry
Maintenance, Test & Measurement, Calibration
Multotec has developed a range of composite integrated mill liners in response to the needs of local and international mining clients.
Read more...Rich rewards result from investing in WearCheck’s training Wearcheck
News
A priority for condition monitoring specialist, WearCheck, is to ensure that customers whose maintenance staff undergo technical skills training earn significant returns from their investment into the training. Maintenance crew members can choose from more than 15 courses that are conducted by WearCheck’s experts in various categories of condition monitoring.
Read more...The criticality of maintenance in the water and wastewater segment Schneider Electric South Africa
Maintenance, Test & Measurement, Calibration
In a time of water shedding, climate change and ageing infrastructure, the importance of maintenance and support in the water and wastewater segment cannot be overstated.
Read more...Quality test tools save costs at pulp and paper mill Comtest
Editor's Choice Maintenance, Test & Measurement, Calibration
A case study on how preventive maintenance and a few good test tools avoided unnecessary motor replacements at a pulp and paper company.
printer friendly version