Interpreting results for the new ASTM standard for varnish potential
June 11 2013 -
Turbine oil varnish has been a well-documented reliability challenge for power plants. Traditional oil analysis techniques have been ineffective at predicting the onset of deposit problems in turbine oils – often defined as varnish. This has led to the commercialization of several new analytical tests which measures oil degradation products and can be correlated to the potential of deposit formation of turbine oil. The most widely adopted test is referred to as Membrane Patch Colorimetry (MPC).
Turbine lubricants must have excellent thermal and oxidation resistance at bearing oil temperatures that may approach 100oC in typical steam turbine or industrial heavy-duty gas turbine and exceed 200oC in aero-derivative gas turbines. Turbine lubricants must control the rust and corrosion that could destroy precision surfaces, resist foaming and air entrainment, which could impair lubrication and lead to equipment breakdown, and have high viscosity indexes that allow more uniform lubricating performance over a wide range of ambient and operating temperatures.
Performing oil analysis tests to determine the presence of varnish in a system is challenging for a few reasons.The sample of oil that is obtained for analysis may not be indicative of the condition of the lubricating system. If the lubricant in a heavily varnished system is changed without performing a flush to remove the deposits, the new oil may initially indicate a low varnish potential even though there are deposits throughout the system.
The myth about a brilliant scientist developing a new invention to change our world is exactly that…a myth. It is well accepted that scientists, engineers and practitioners of all walks of life build upon other’s thoughts, inventions and ideas.