Understanding & Measuring Turbine Oil Cleanliness

15 July 2022

AUTHORED BY: Reliability360

Making sure your equipment is healthy and running at optimal levels starts with the oil. Without clean oil running through your systems, you run the risk of not only severely damaging your machines but also affecting your bottom line with unplanned downtime. In fact, revenue during peak seasons can account for millions of dollars in profit, and poor selection and maintenance of your turbine oils can result in production losses equaling more than half a million dollars a day. One of the best ways to prevent this is with your turbine oil cleanliness.

Cleanliness is one of the most important factors to consider when looking at the health of your turbine oil and machines, thanks in part to global competition. When global competitors are manufacturing overseas at a lower cost, maintaining a precise level of reliability and uptime is necessary to keep costs manageable. Contaminant-free lubricants and components will extend the lifetime of both, increasing the overall reliability of your equipment while keeping your bottom line in mind.

To effectively measure the cleanliness of our oils, the International Organization for Standardization (IOS) developed a cleanliness code, which is used as the primary reviewed piece of data for most industrial oil analysis reports. Achieving cleanliness targets for your oil is not an overnight process, but it can lead to major extensions in both your machine life and your turbine oil service life.

Particle Counting

But what do you do employ particle counting on your turbine lube oil, and you discover you have two units with different particle counts? Why does this happen and what does it ultimately mean for your valuable equipment and machine health?

Several areas need to be considered when first approaching the problem. The first thing to consider is the sampling procedure. If the sample is being pulled from a problematic area, such as a sump drain, or if the sample is being performed using a questionable method, such as drop-tube sampling, you can expect erratic particle count results.

This is because these methods do not result in quality representative conditions of the level of contamination or wear. Instead, best practices should include actions like installing a primary sample port in the return line before dumping into the sump. You can also install secondary sampling points after each lubricated component or bearing. This allows you to pinpoint the source of a problem that was identified using the primary sample point.

But if you are sampling properly or using a continuous system for particle counting, you will be able to properly trend and take action on particle count results.

Defining Cleanliness Targets and Alarms

For most filtered machines, contamination levels evolve to a stable state. They rise or fall on their own until stability is reached. This assumes a constant ingression rate, a constant filtration capture efficiency and a constant oil flow rate through the filter(s). Should any of these conditions change, equilibrium is lost until it is re-established later at another level. It’s a mass balance, i.e., particles entering from ingression must equal the particles removed from filtration.

This stable state of cleanliness must be within the target cleanliness level set by the reliability team. Target cleanliness should be aligned to the machine’s Optimum Reference State (ORS).

For most all machines, the correct ORS cleanliness target is driven by five important factors: criticality, environment severity, contaminant tolerance, proactive maintenance and predictive maintenance.


This is a combination of the cost of repair and the cost of failure (downtime, safety, machine readiness, etc.). Criticality analysis helps address the cumulative consequences of machine failure and can be used to help make decisions about your cleanliness targets and alarm levels.

Environment Severity

This relates to the likelihood of contaminant invasion and the subsequent damage to critical machine surfaces. The three main considerations are the density of contaminants in the work environment, the effectiveness of the machine to prevent ingress of these contaminants, and the ability of the filter(s) to rapidly remove and retain ingressed contaminants.

Contaminant Tolerance

Not all machines have the same sensitivity to particle contamination. Some are reasonably tolerant, but most are not. At least 10 percent of all critical machines have a hypersensitivity to particles of a certain size and concentration.

Proactive Maintenance

Proactive maintenance seeks machine life extension by systematic eradication of root causes like particle contamination. The cleaner the oil, the longer a machine’s life expectancy. Proactive maintenance brings critical root causes such as particles into focus. Noria has published extensively on this important subject.

Predictive Maintenance

While proactive maintenance seeks life extension, predictive maintenance seeks to detect the onset of machine failure and predict the remaining useful life (RUL). It’s a tough job, but when done with the right tools, methods and skills, it is highly effective. With oil analysis, predictive maintenance targets wear particle detection and characterization (analytical ferrography, etc.). The effectiveness of wear particle analysis is much improved when oil is clean.

Wear particle detection chart showing how cleaner fluid allows for faster problem detection.

Background contamination can mask the ability to enable early detection of abnormal wear conditions. High background particles in Case A result in a short detection time window compared to Case B. Digital particle counters that can identify wear particles by type can offer similar benefits.

Turbine Oil OEM Recommendations

When it comes to the oil makeup, lubricant suppliers create them using the formulations developed by the original equipment manufacturer (OEM). OEMs have identified suggested or recommended lube oil performance test criteria and typically stipulate that an oil known to perform successfully in the field may still be used even if all recommended values have not been satisfied. These standards help provide valuable insight into the overall performance and life expectancy of turbine oils.

The original equipment manufacturer’s recommendations for turbines can be as high as 16/13. But, significant improvements in reliability and equipment life can be achieved by setting target values lower than those recommended by the OEM. For example, if all the equipment’s conditions are performing optimally, reducing the target cleanliness zone from 16/13 to 14/11 will allow the life to be extended 1.5 times more when compared to a machine set at a 16/13 target cleanliness level.

In order to achieve these target levels, proper contamination control measures should be in place. These include

  • Quality desiccant breathers
  • Hybrid breathers
  • Serviceable seals
  • Full exclusion from the environment to include lube top-up and change procedures
  • Quality Beta-rated filters.

There is a common philosophy among industry professionals that states the cost of excluding a gram of dirt is only 10 percent of what it would cost to remove it once it gets in your oil. Paying the up-front cost to keep contaminants from entering your systems will save you exponentially more in the long run than if you allow contaminants to enter your systems.

If you have two like units with the same contamination control equipment and practices in place, but one is showing a higher level of contamination, an inspection as to the source of contamination is warranted. Aim for your target values and watch for any significant increase in contamination that may be cause for corrective action. If you have a system that can identify wear particles by type, it is easier to pinpoint root causes and find a solution before catastrophic failure occurs.