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Setting Limits on Fluid Properties


Earlier this month, I talked about how we set limits for wear metals and contaminants. There is one final group of results Data Analysts examine to determine the health of oil, fuels, and coolants: fluid properties.

Fluid properties are the physical and chemical features that allow the fluid to perform as it was designed. Viscosity, Acid Number, Base Number, Oxidation, Nitration and Additives are the main fluid properties examined by fluid analysis.

These properties don’t have much in common. Different tests are used to determine if the fluid still has the ability to protect equipment. Viscosity needs to be run at different temperatures to match the operating conditions of the equipment, ICP is used to quantify the metals found in common additives, oxidation and nitration are measured using FTIR, and acid number and base number need to be run using different titration methods to get the measurement we desire.

Just like wear metals and contaminants, the actual flagging limits depend on what the fluid is, the equipment the fluid is being used in, and what application the equipment is doing. These factors all can change the maintenance recommendations from the Data Analysts, which is why it is important to provide as much information about the sample as possible.

To learn more about the challenges facing each fluid property and how we set our flagging limits, please download this technical bulletin.

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Setting Wear Metal Flagging Limits


Our customers have a wide range of knowledge about fluid analysis. Many are new to the process and others have decades of experience. Some have even earned tribology certifications or degrees. Our Data Analysts end up talking to all of them, so we receive a wide variety of questions every day.

Occasionally, our experienced customers compare our test results to the wear metals flagging limits set by the original equipment manufacturers (OEMs) and we often get calls asking why we don’t follow the OEM’s recommended levels. Fortunately, this is an opportunity for us to explain the value of analysis from POLARIS Laboratories®.

We have analyzed millions of oil samples on most types of equipment, meaning we have a huge pool of data and customer feedback. We use that information to make sure our flagging limits won’t have customers perform maintenance too early or too late. Giving precise recommendations saves customers time, money, and effort, but we want to make sure that equipment is protected, too.

In addition to evaluating individual wear metals, the combinations of wear metals are also significant. Combinations of wear metals are significant because they may indicate a particular alloy, which is vital to understanding if a specific part is wearing – for example, elevated copper and tin would indicate a bronze part is wearing.

Many OEMs publish wear metal guidelines. These general guidelines may be a place to start to understanding fluid analysis reports, however they are not designed to be used as absolute values. To maximize the value of fluid analysis, a customer should expect a credible laboratory to have a comprehensive database, utilize statistical analysis to refine flagging limits, and have qualified Data Analysts to make appropriate maintenance and reliability recommendations.

For more information about how and why POLARIS Laboratories® adjusts flagging limits, download our new technical bulletin.

Proven Impact. Proven Uptime. Proven Savings.
Let us prove it to you.

Published September 11, 2014

How We Set Flagging Limits


In the Data Analysis department, one of our key responsibilities is to answer any questions customers have about fluid analysis. A lot of our calls are about what results mean. Does the fluid need to be changed? What could be causing that strange noise? We also get questions asking for testing recommendations for a specific application or issue being seen. However, the hardest questions to answer are about our flagging limits. The only easy answer for these questions is: “It’s complicated…”

Our process for defining flagging limits is actually something that we are quite proud of. It can be difficult to provide our limits because they are very dynamic and specific to the information provided about the equipment, fluid, and application. For example, one engine in your fleet may have different flagging limits than another because our limits are customized based on the specific equipment manufacturers and models. Limits are also affected by the rate of change from prior samples. Individual severities may change based on other results that are flagged. These are just a few scenarios that affect limits, but I think you can begin to understand some of the complexities surrounding our limits.

We’d like to clear up some of the confusion by publishing a series of articles to address the more common questions surrounding flagging and alarm limits. What aspects of your report flagging have you been curious about? Post your questions in the comments section of this blog so we have an opportunity to reply and use your questions to guide the topics of our articles.

Proven Impact. Proven Uptime. Proven Savings.
Let us prove it to you.