Flagging Limits: Considerations Before Making Changes

Flagging limits (also known as alarm limits) are essentially threshold values used to identify when an oil or grease sample has gone beyond its “healthy” condition. These limits help maintenance and reliability specialists determine machine health based on wear and contamination parameters and oil/lubricant quality based on physical and chemical properties.

How are Limits Set?

There are at four main ways flagging limits are set for oil analysis reports: no predefined limits, industry standards, statistical analysis, and rate-of-change (trending).

No Predefined Limits

This methodology is based on human judgement – the experience of the lab analysist and their interpretation of the data. Included in the analysis is the type of equipment and lubricant information provided.

Industry Standards

Most major OEMs have some type of oil analysis flagging limit recommendations.  Some may be model/brand specific while others might be general guidelines for a certain fleet or oil grade.  Oil manufacturers are more likely to provide some flagging limit guidance on analysis results such as viscosity, additives, oil degradation (oxidation, acid number) while heavy equipment manufacturers are more likely to provide limits on oil cleanliness (particle counts, contamination concentrations, water) and wear metals. These industry/OEM standards may not always be available for lubricated machinery found in industrial plants.

Statistical Analysis

Flagging limits can also be set through statistical analysis of sample data in order to establish a solid baseline. Software, such as myLab, can generate statistical histograms based on thousands of samples and grouped by component type, equipment manufacturer, equipment model, oil type (manufacturer, brand, and grade), industry, and equipment application.

Rate-of-Change / Trending

Rate-of-change or trend-based limits are the mathematical method used by lab analysts if absolute limits (as noted above) are not available. A trending difference from “normal” or baseline would trigger the alarm.

Learn more about how Fluid Life determines flagging limits.

Considerations Before Customizing Flagging Limits

If you run into a flagging limit that you disagree with on your oil analysis report, you now have the ability to change those limits on a component or global bases for your organization. To gain access to custom flagging limits, contact your Account Manager to enable the ability to manage your flagging rules in myLab.

However, before making any changes, you should follow through with our three stage Data Interpretation Process to make sure you’re getting all the necessary inputs to manage the change effectively.

Interpretation stage

In this stage, you need to determine a number of factors that could have impacted on your sample results. It may be that the flagging limits are correct, but the results are suspect because of issues around your sampling processes and procedures. This can include a review of:

• Sampling points to determine if they are in the right locations for a representative sample to be taken
• Sample procedures to ensure consistency in how samples are pulled and submitted
• Sampling frequency to determine if samples are taken consistently on schedule
• Sample turnaround to review the transit time and processing time for your samples to see if there’s any way to improve
• Sample data integrity to ensure accurate data is collected and registered to ensure the lab has the data they need to process the sample accurately (e.g. oil type, service hours, unit / component, etc.)

In addition, you should consider if this flag (or lack of flag) correlates to other condition-based data or real-world performance of this particular component that may impact on results. Finally, you can also gain more perspective by contacting us to review your results more in depth or gather insights from equipment manufacturers, oil suppliers or other sources to help build consensus around the issues.

Decision Stage

After working through the data gathering process in the Interpretation Stage, you now need to consider if a change is required or not. For example, if you found that there are issues with your sampling procedures, fix those issues first, re-sample, and then re-evaluate whether the flagging limit change is still required.

Response Stage

This is when you take action based on your decision. For example, you could decide to monitor results for the next six months before making any flagging changes. Or, based on a review of historical sample data, your unique environmental conditions, and OEM recommendations, you determine that the default flagging limits need to be loosened or tightened. Whatever you determine is the right course of action for your organization, if you need support with the implementation, Fluid Life can help.

Communication

With any flagging limit change, communication to your team is important. They need to be fully aware of the implications of the adjustment and understand how to interpret the data based on the new limits.

Additional Resources

• Article: Manage Your Flagging Rules
• Article: Flagging Limits
• Article: Sample Rank
• Brochure: Flagging Optimization