CONDITION MONITORING FEATURE
TURBINE OIL
Assessing Oxidation Condition and Lubricant Refreshment in Turbine Oils
By Andres B. Lantos, WearCheck Argentina* * Dave Wooton2
, Sebastián Lauría1 , Andrés Bodner1
Abstract Turbines are critical pieces of equipment for power plants and related industries. Varnish formation is the first root cause for downtime and loss of reliability in turbines. The lubricant’s oxidation con- dition can be effectively
monitored
through RULER (Remaining Useful Life Evaluation Routine), MPC (Membrane Patch Colorimetry) and RPVOT (Rotating Pressure Vessel Oxidation Test) tests. Be- sides the nominal ASTM (American So- ciety for Testing and Materials) value for these tests, significant information can be gathered from digging into these tests and integrating their outcomes. One ma- jor application for this integration is the estimation of the lubricant refreshment for lean operation. Through lab tests, this can be accurately estimated, by planning ahead of the upcoming maintenance in- tervention. This method will be shown, together with case studies.
Introduction Turbines are essential components for power generation and heavy industries, where downtime and failures can result in production loss, penalties, and opera- tional disruption. While wear in turbines occurs primarily due to poor lubricant
, Gabriel Lucchiari1 , Esteban Lantos1
1 Laboratorio Dr. Lantos – WearCheck Argentina. Buenos Aires, Argentina. 2 Wooton Consulting. Beaverdam, VA 23015 USA
To prevent oxidation, turbine lubricants contain around 1% antioxidants, which protect the base oil from thermal and oxidative stress.
condition, the primary cause of turbine failure is the accumulation of depos- its, leading to issues like sticking valves, blockages, and inefficient heat exchange. Varnish, often linked to oxidation pro- cesses, is a common type of deposit that forms as a result of sacrificed antioxi- dants and oxidation byproducts. Varnish removal incurs high costs in terms of downtime and equipment replacement, making the monitoring of turbine oil ox- idation condition crucial. To prevent oxidation, turbine lubricants contain around 1% antioxidants, which protect the base oil from thermal and oxidative stress. While the generally ac- cepted threshold for using turbine oils is
when the remaining active antioxidants are at 25% of the original formulation, varnish issues can emerge even when re- maining antioxidants are as high as 60%. Maintaining a high dose of antioxidants and low varnish potential is essential to ensure reliable operation, and lubricant refreshment can play a pivotal role in achieving this goal.
Analytical Techniques for Lubricant Evalu- ation Three key tests are used to evaluate the oxidation condition of turbine lubri- cants: RULER (Remaining Useful Life Evaluation Routine), MPC (Membrane Patch Colorimetry), and RPVOT (Rotat- ing Pressure Vessel Oxidation Test). These tests provide valuable insights into the oxidation condition and the remaining antioxidant levels.
Membrane Patch Colorimetry (MPC) (ASTM D7843) is a method for determin- ing varnish formation in mineral turbine oils. In analytical chemistry, procedures can be classified as either end point or standardised. Typical end-point proce- dures are titrations such as Acid Num- ber (ASTM D974) or Karl Fischer (ASTM D6304). MPC involves heating the lubri-
Figure 1. MPC is a standardised method in which precipitation time is critical (part I). 30 LUBEZINE MAGAZINE | SEPTEMBER 2023
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