Maintenance, Test & Measurement, Calibration

Assessing oxidation condition and lubricant refreshment in turbine oils

March 2023 Maintenance, 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.

To read the full story visit


Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Asset reliability care field dominated by WearCheck
Wearcheck Motion Control & Drives
Condition monitoring specialist, WearCheck has solidified its position as a leading player in the asset reliability care sector.

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.

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.

How dry ice blasting is revolutionising the mining industry
Maintenance, Test & Measurement, Calibration
Dry ice blasting has emerged as a game-changing technology for the mining industry, offering a range of advantages that are reshaping traditional cleaning methods.

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.

WearCheck at Mining Indaba 2024
Wearcheck News
Specialist condition monitoring company, WearCheck, showcased its range of mining-related predictive maintenance techniques, products and services at the 2024 Investing in Africa Mining Indaba.

The logical solution to oil and gas industry corrosion
Maintenance, Test & Measurement, Calibration
The consequences of corrosion in the oil and gas industry can be astronomical. The simple culprit is metal reacting with oxygen and moisture, degrading it back to its natural state.

Lube tip: foaming is affected by oil level
Wearcheck Maintenance, Test & Measurement, Calibration
In a circulating system, it is crucial to check the oil level before introducing anti-foam agents to address a foaming problem.

WearCheck extends its footprint to second India lab
Wearcheck News
Condition monitoring specialist, WearCheck recently opened its doors to its second laboratory in India – this one in Durgapur. This follows the success of its Chennai-based laboratory, which has operated successfully since 2010.

WearCheck expands its skilled workforce
Wearcheck News
Condition monitoring specialist WearCheck provides a range of predictive maintenance services to help extend the life of industrial machinery. The company recently brought in additional talent to ensure that its growing customer base continues to enjoy outstanding service.