For an asset as valuable as a Gas or Steam Turbine, you’ll be thinking that all regular maintenance activities are carried out on time and correctly; but whilst vibration levels along with temperatures and pressures are monitored routinely to look for any signs of performance degradation or untoward changes that could affect the continued operation, wouldn’t it be beneficial to know just how well the Lubrication system is performing? In this article, I will be explaining all you need to know about what Turbine Oil Analysis is.
Why Should You Undertake Turbine Oil Analysis?
Changing the oil in your turbine is expensive, monitoring the performance and additive levels are not. This data will give you a trend that allows you to schedule and budget for the costly oil change.
What parameters for the lubrication system are checked, other than ensuring the reservoir content is sufficient and oil pressure and temperature are within the expected limits? The presence of Chip detectors and filter DPI gauges provide an indication that there is a build-up of debris.
Would it be beneficial to know how the oil is performing in relation to the design standard? You could say that temperature and pressure values are sufficient to satisfy this requirement. However, those aspects do not show the chemical changes which are occurring in the circulation system content.
How much longer will your oil continue to provide the key functions of cooling, lubricating, and protecting. The expense involved in changing out the oil for these assets is not something that can be taken lightly, so carrying out a premature change to be on the ‘safe side’ brings that forward, but at significant cost. Also if you have no analysis how do you know if your change is premature or too late?
When Should You Complete Turbine Oil Analysis?
At regular intervals, samples should be sent away for analysis to assess several key aspects of the lubricant’s chemistry, examine the physical properties of the oil and identify any contamination. Monthly analysis should be carried out to keep trends relevant for the basic analysis suites. The full turbine suite to include the oxidative ability and remaining antioxidants should be carried out at a minimum every 6 months.
What Tests Are Completed As Part of Turbine Oil Analysis?
A full turbine oil analysis suite should consist of the following:
| TEST | TEST METHOD | DESCRIPTION |
| Rotating Pressure Vessel Oxidation Test (RPVOT) | D2272-14a | This test evaluates the oxidative stability of the lubricant. The lubricants ability to resist oxidation and degradation under high temperatures, water contamination, oxygen, pressure, and a copper coil catalyst. |
| Remaining Useful Life Evaluation Routine (RULER) | D6971-09 + D6810 | This test monitors the % of remaining amine and phenol additives (which are primary antioxidants) compared to the new reference oil. These additives basically neutralise by-products of oxidation to stop the cycle of oxidation. |
| MPC Varnish Potential | D7843-18 | This test filters out the insoluble matter of turbine oil. The insoluble matter is then heated up and the colour is recorded using a spectrophotometer. This value is proportional to the lubricants potential to form harmful varnish and sludges. |
| Visual Inspection | n/a | The visual appearance of the oil and any particulates is noted to support the analytical results of the other tests. |
| Ferrous Wear Content (FW) | D8184 | A total measure of ferrous particles in the sample irrelevant of size. |
| Elemental Analysis | D7303-12 | Measures several elements to identify wear issues, contaminant levels and chemical composition of the lubricant |
| Viscosity at 40°C | D7279-14A | A quality check to ensure the lubricant is still in the specification and therefore retaining its ability to lubricate. |
| ISO Particle Count | ISO4406 | The particulates within the sample are analysed and counted to identify any particulate contamination issues. |
| Total Acid Number (TAN) | D66411A + D974-14E02 | The total acid number allows the acidity of the lubricant to be analysed which gives us a trend and allows us to predict when oxidation is occurring. |
| PPM Water Analysis | D6304-07 | The CKF is used to determine the water content of the lubricant. This is compared to the reference oil to account for known additive interferences. |
| Fourier Transform Infrared (FTIR) | E2412 | This allows the used lubricant result to be overlayed with the spectrum from the reference oil which will show changes to the chemical composition of the lubricant over time. Indicates oxidation, nitration, sulphation and contaminants. |
| Bacteria | D6974-09R13E2 | Allows us to determine if any microbial growth is likely to occur in the oil tank due to steam, condensate or water contamination. |
What Does A Turbine Oil Analysis Report Look Like?
A typical turbine oil analysis report is shown below. You can download our example turbine oil analysis report by clicking here.
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