Grease has been used since ancient times, and new technologies and equipment design require us to improve our understanding and perception of it. These advancements enable those working with grease to recognize better its impact, effective properties, and the proper methods for testing grease samples, shedding new light on its applications and benefits.

The Importance of Monitoring Grease

Through these continuous technological advancements, the formulations of grease have significantly expanded, making it a crucial component to monitor when maintaining and enhancing the performance of modern equipment across various industries.

Greased equipment in mobile and industrial industries is getting more scrutinized as predictive and proactive maintenance are becoming the standard. To this end, greased components need to be viewed as crucial as any lubrication program, and any downtime resulting from failed greased components should be thoroughly investigated to determine the cause of the failure. Was it environmental conditions, over or under lubrication, incorrect grease, or exceeding the equipment design capacity?

The Benefits of Grease Analysis

By testing grease components, analyzing and recognizing wear trends, and determining lubricant properties, we can increase the capacity to react to potential equipment failures. These failures can lead to a reduction in production and compromised safety. While many industry sectors view greased components as replaceable or run-to-failure parts, testing these components allows us to become more informed.

Technological advancements now allow for precise determination of wear concentration and lubricant conditions. With routine testing, we can identify and provide the information to better schedule lubrication intervals, plan equipment repair, and determine the best time to replace components, thus increasing uptime and productivity. With this knowledge, industries can effectively conduct Root Cause Analysis (RCA) to prevent future failures.

Today, failure can be prevented with as little as 2 grams of grease. ATSM D7718-11 Standard Practice for Obtaining In-Service Samples of Lubricating Grease was created to make the process more accessible. This standard describes the method to obtain in-service grease samples that can be tested for trending purposes.

The basic tests, which include Ferrous Density, FTIR, color, and water, are used as a screening tool.

In addition, more complete evaluations of grease include testing for Total Water, Remaining Useful Life (RUL) Antioxidants Levels, Microbial, Elemental Metals, and Extrusion Values. These tests’ key component is for each to be compared to a known provided baseline sample.

The Wear that Grease Testing Identifies

Data obtained from grease evaluations can assist in identifying not only the characteristics of the grease itself but also the quality of the base oil it provides for lubrication.

Effective grease should lead to minimal wear metals. Elevated levels of antioxidants with extended Remaining Useful Life (RUL) across several samples may indicate a need to reassess current relubrication schedules. Proactive monitoring of these factors can reduce lubrication expenses and ensure consistent reliability.

On the other hand, a high wear metal concentration could be a sign of an increase in lubrication, as this would lead to the base oil not providing the correct fluid film for protection.

The National Lubricating Grease Institute (NLGI) grade measures the hardness of grease in relation to pumpability and soap structure, and the ISO Viscosity grade provides the proper fluid lubricant film protection. In addition, tools such as the Analytical Ferrogram give insight into the type of wear being generated and are a great aid in the RCA process.

For example, when analyzing a recent grease sample with severe levels of Ferrous Debris for a crane wheel bearing, it was recommended that an analytical ferrogram be performed. The amount and type of wear observed indicated insufficient lubrication was occurring, yet regreasing was being conducted at regular intervals.

There was no indication that the bearing was in failure mode. However, an abundance of fresh wear was generated. And, since the lubrication regime was boundary, the base oil viscosity plays an important role. Usually, with a slow-moving crane bearing, a base oil Viscosity of ISO 320 or 460 is standard.

This grease being tested had a base oil Viscosity of ISO 220, which caused an increase in wear as the lubricant film was insufficient for the heavy loading occurring. A recommendation was made to contact the crane manufacturer for further guidance on the proper grease for that operating condition.

Looking through this new lens of analyzing grease, adding regular testing on grease components can help reduce unnecessary downtime and increase overall safety.

One of the goals of Root Cause Analysis (RCA) is to identify the factors leading to an event that resulted in an undesired outcome and to develop corrective actions to prevent such results from recurring.

In maintenance, recognizing patterns during analysis can provide insights into severe outcomes, such as increased wear, which can be detected through ICP elemental analysis, elevated ferrous values by Particle Quantifier, or Ferrous Density.

It is crucial to differentiate the appropriate measures when conducting RCA. This can shift the analysis method entirely from immediately shutting down the equipment, using additional conditional monitoring technologies, or allowing other processes to assist in determining the root cause.

Technologies and Impact on the RCA Process

• Vibration Analysis can confirm a defect in the rolling element but, in some instances, only confirms the wear seen in your fluid report and can lead to a diagnosis to disassemble and replace
• Ultrasonic Analysis is more suitable for mobile equipment and offers higher advantages for slow-rotating equipment
• Thermography can indicate elevated temperatures of the running equipment

Despite these technologies providing dependable results, these tools cannot determine the amount or type of wear being presented. Fortunately, those familiar with the Analytical Ferrogram already have access to a tool to assist.

Since the fluid analysis should already be completed, the next step is to request that the Analytical Ferrogram test be performed. Tests should be requested within a reasonable time frame and recommended as soon as you get the fluid analysis results or within 30 days, depending on your fluid analysis laboratory.

This is due to how the wear metals in the fluid analysis report relate to the wear metals observed on the ferrogram. You could also submit a new sample to verify the elevated wear and request an analytical ferrogram on that sample.

A Picture is Worth a Thousand Words

Over the years, customers have used this process to determine whether disassembly is warranted. However, the average size of particles observed falls well below the visual size of what the eye can see, meaning the damage typically cannot be observed as easily once torn apart.

There needs to be more than just a visual inspection when determining wear, for example, within the United States Navy, where they implemented a Planned Maintenance System (PMS) involving scheduled intervals to disassemble equipment, inspect for wear (sometimes measuring it), and reassemble the components In many cases, the U.S. Navy observed no significant findings and repeated this process over time, eventually leading to the practice known as “gun decking” or “pencil whipping.”

During Analytical Ferrography, the laboratory analyst reviews the ferrogram under a microscope and interprets the results. This helps apply severity to the amount and type of wear observed, and depending on the analysts’ experience, the observation can assist in providing the needed interpretation to the customer.

Regarding microscope analysis, training on the microscope is needed to observe the debris and truly understand how the contaminants and wear debris were generated within the system. A few critical observations considered while analyzing include:

• The purpose of the requested ferrogram
• The customers (understanding) with control
• The equipment’s environment (clean, dirty, hot, cold, etc.)
• The equipment manufacturer and model
• The lubricant type and grade
• The additives used and their purpose

Most of these items can be found in any article on the web. Sometimes, the missing element in fluid analysis is the equipment’s duty cycle, which is more in the realm of the customer’s understanding than the laboratory analysis.

Most often, fluid time and unit time are the hallmarks of determining the relation of wear occurring. However, understanding the unit’s duty cycle is essential when analyzing wear under a microscope.

Analyzing the Duty Cycle

The duty cycle is called the run time versus rest time, on-off-on cycle. Depending on the equipment, the duty cycle can occasionally have more inputs.

Information like cycle time and the material being moved or loaded must be included. For an excavator, the duty cycle is defined as pre-digging, digging, lifting, unloading, and swinging. See Figure 1.

Figure 1 demonstrates an example of the swing portion of the excavator and wear that commonly occurs. Rubbing wear (2 body wear) is normal as the gears will come into contact; the EP additive prevents welding when contact happens.

Next, the viscosity under load will react, slowing the contact and transmit power. However, when the slew bearing wears, it increases loading for the gear box. Excessive backlash will also increase wear and overload the lubricant’s protection ability.

This can create three-body wear, usually in the form of fatigue particles or an elevated number of laminar particles formed by flattening larger particles between surfaces.

In the example seen in Figure 2, a wheel loader duty cycle, which is the time it takes to drive forward into the mound, scoop, reverse, swing loaded dump, and repeat.

Figure 2 illustrates that the lubricant facilitates power transmission and offers protection against wear and loading when necessary. However, due to usage, wear can still occur if the load capacity exceeds the lubricant’s limits.

By studying the relationship between wear and lubricant protection and incorporating the duty cycle process, one can better understand the wear patterns observed in the report.

Example Guide for Analyzing Ferrogram Results

A customer submitted a sample of a crane wheel, which was lubricated and on a routine maintenance schedule, and the laboratory performed an analytical ferrogram on the sample. A ferrogram identified why wear was occurring.

The results showed the equipment was experiencing rubbing wear, fatigue wear, and laminar wear. The crane wheel was a grease bearing with NGLI 2 with a 220 cSt base oil with an average air temperature for the crane of 110 to 125 degrees F.

The amount of rubbing wear and three body wear indicated the possibility that the base oil was not providing the necessary fluid film thickness at elevated temperatures and loading capacity.

In this case, the customer was recommended to contact the manufacturer about using a higher-viscosity base oil to provide more protection.

Fluid analysis laboratories offer a wealth of helpful information for interpreting the results of an analytical ferrogram. These valuable resources enable customers to take necessary maintenance actions to address current wear conditions and prevent them in the affected unit and other units within the fleet in the future.

References:

https://www.epa.gov/moves/epa-nonregulatory-nonroad-duty-cycles