Executive Summary
When it comes to failure root cause analysis, many TLT readers report evaluating the lubrication process holistically. Some common elements include used oil analysis, checking OEM specifications, conducting testing and reviewing data. These protocols must be repeated over time to monitor changes in lubrication and conditions.

Q.1. In your failure root cause analysis (RCA), how do you check that the lubrication of the component complies with the fundamentals of lubrication?

Oil level, oil type correct, oil performance (4 ball tester).

Used oil analysis, viscosity, wear metals, contaminations, total acid number (TAN), water, etc.

Lubricants are a complementary component, hence I do not perform lubricant checks.

Check with the OEM to see if specified lubricant meets their lubrication needs and secondly if lubricant viscosity grade and other properties are reasonable.

Since internal or external operating conditions can change unexpectantly, it is imperative that daily observations be logged and viewed on an ongoing basis.

Completely, plotting Stribeck curves and examining the failure of the surface is critical to proving a viable application.

Wow, this is a wide open question as it could relate to so many type of lubricants or applications. I guess to answer from helicopter down, first and foremost you would make sure the used lubricant meets its chemical backbone and is not destroyed from use in application. You would also make sure recommended lubricant meets the specification of the application or OEM. You would also have to look at the failed component; was it made properly (bearing or something) where it wasn’t an issue with construction? It is more than just looking at lubricant, it is the whole process that needs to be looked at holistically.

Contamination, oil degradation and over or underlubrication.

In an RCA, I treat “lubrication fundamentals” as a checklist of the five rights (right lubricant, right amount, right place, right time, right condition) plus operating context. I verify them with evidence from documents, hardware inspection, oil analysis and operating data.

There are two aspects to this: 1.) reviewing the failed components for evidence of lubrication related wear\damage and 2.) reviewing the condition monitoring data (vibration, oil, thermal, etc.) for signs of lubrication issues.

Viscosity, fundamental chemical analyses, surface analyses with tribochemistry, wear mechanism.

We use SOS monitoring for oil analysis, analytical ferrography, wear trends and vibrations.

The lube must be clean and dry and have the performance properties in a healthy state.

For metalworking fluids, you cannot always determine the exact cause of failure. It is best to mentally keep thinking in terms of a hypothetical Stribeck diagram. Usually more than one region of the Stribeck diagram applies. If the current lubricant is not working adjust your product to shift positions on the diagram and cover other areas.

This is not consistent across all our sites (I work with several). Some sites are better than others, very dependent upon the RCA facilitator.

Calculations to predict scuffing and wear probabilities and influence on fatigue life.

Check operations manuals and lubrication requirement specifications and product technical data sheets.

I first check that the correct lubricant was installed; this is done by investigating the maintenance records, and investigating the lubricant inventory within the service area. (Confirm that the proper lubricant was used and available.) Next I check to see what the nature of the failure is, contamination, heat stress, filtration, etc—if it is a pressure type system to see if pressure is within specification. Next I perform a basic review of the fluid for wear materials, looking beyond the failed parts. In the event that I find that the lubricant was not the correct type or had been incorrectly selected, I research the purchase records and ask who had the authority to make the decision to select the replacement lubricant.

We use an oil monitoring program which measures a broad range of properties.

We contact specialists from a cooperating laboratory specializing in lubrication and analyze historical cases. We usually agree on the procedures to be followed in such cases.

That type of knowledge comes with experience and education. There are times when experience can lead to making better a diagnosis than anything else.

Checking wear, deformation, discoloration, vibration and noise.

That starts with examinations of the failed parts. Usually, a visual inspection, followed by microscopy, can tell if there was a lubrication problem. If there is a lubrication problem, then all the details of the machine history and operation would be looked at.

Not applicable for our RCA.

1.) Visual inspection. 2.) Oil analysis. 3.) Wear debris analysis.

Check oil analysis, maintenance records and what type of lubrication was used and if it followed the manufacture recommendations.

We review the specification of the grease used and compare it to the operating conditions of the equipment. As a second step we sample the lubricant from the failed application and if the sample allows, compare it to what was recommended. If the three things do not match, we then focus on the lubricant.

Analysis of the lubricant and compare it to OEM recommendation.

Ensure that the oil used complies with OEM recommendation/design requirements.

Carry out the respective testing of the lubricant, i.e., infrared (IR) scan (show contaminants present), metals (to ensure they are in line with standards).

By performing analysis of the main lubrication parameters, which could include particle quantification (PQ) index, IR, inductively coupled plasma (ICP), viscosity, viscosity index (VI), oxidation, nitration, sulfation, etc.

Starting with the OEM recommendations, studies are done on the used lubricant and operating conditions, like speed, load, temperature and number of hours, etc.

From the oil analysis data to identify questionable practices such as wrong oil, extended drain and contamination ingress. 

First, is there any lubricant left? “It does not matter which lube you did not lubricate with!” Second, viscosity: does that meet the requirement of the lubrication regime of the application? Third, was the fill level correct? Fourth, if the application is a wet brake, clutch, etc., is the coefficient of friction in the application correct? Five, application temperature: Was it a low temperature failure? A high temperature failure? Six, load: Was the application in use, or just sitting and corroding quietly away?

Laboratory oil analysis, online sensors and tribology testing.

By conducting elastohydrodynamic lubrication (EHL) calculations with thermal correction factors applied. If the wrong lubricant viscosity is applied to the application, metal to metal contact may occur leading to shortened component life. “The right lube, at the right time, in the right amount.” If solid debris contamination occurs, three-body abrasion will be an issue as the debris bridges the gap between lubricant separated surfaces. In EHL regimes, solid debris causes stress risers that lead to particle denting on load bearing surfaces. Contamination must be controlled. Water and air offer cooling but do not lubricate. They too must be controlled.

Do you check if the components are lubricated in compliance with the actual operating conditions?
Yes 81%
No 19%
Based on an informal poll sent to 15,000 TLT readers.
Check OEM requirements and specifications; in the case of grease, calculate the required base oil viscosity due to load, size of bearing and speed.

1.) Define the tribological duty. 2.) Verify the correct lubricant was selected. 3.) Check whether the lubrication regime was achievable. 4.) Confirm the right quantity. 5.) Check timing and interval.

OEM guidelines in the maintenance manual is the starting point, then looking at operating conditions to see if they are the same or different.

Check the specs if the lubricant matches the manufacturer’s recommendations for the machine. Sample the lubricant for contamination, additive depletion, oxidation. Talk to the machine operator to confirm that the lubricant was obtained from a clean, dry source, etc.; confirm operating conditions had not changed.

1.) Check the viscosity grade, OEM specification and make sure it is suitable for the load and temperature. 2.) Make sure the amount is correct, by checking the oil level indicator. 3.) Make sure the lubrication system is functioning properly by checking the oil pump pressure, flow rate and filter. 4.) Evaluate used oil analysis (UOA) as primary diagnostic tool. 5.) Check operating conditions (temp, pressure, speed, etc.) and make sure they are correct. 6). Conduct physical inspection for component wear pattern. 7.) Check lubrication practice.

Comparison of certificate of analysis with retained sample of the filled batch and with the lubricant in the system.

Used oil analyses tied to equipment component failure. Ferrography on wear particles.

I have not faced lubrication-related failures. Our strategy for lubricant selection is based on engineering calculations that account for the operating conditions (rpm, speed, load, temperature, L10 life, etc.). Furthermore, many machine elements are run-in extensively. 

Q.2. If operating conditions change (which they do over time), how do you ensure that the lubrication is in compliance with the new operating conditions?

Oil performance (four-ball tester).

Used oil analysis, viscosity, wear metals, contaminations, TAN, water, etc.

Lubricants are a complementary component hence I do not perform lubricant checks.

Check VI of lubricant to ensure that it will operate properly in the new conditions (i.e., temperature change).

Based on daily observations, supportive analysis (heat, vibration, noise, etc.) will give reasonable indications of the performance of the lubricants in use.

Laboratory analysis of oil, monthly or quarterly depending on machine criticality and/or historic cleanliness and additive retention.

Building in formulation redundancy and testing the formula during development to stressful conditions, i.e., temperature, oxidation, shelf life and application.

Proper viscosity maintained and timely oil change. 

Monitoring the temperature of the assembly, oil analysis (mainly viscosity) of the samples withdrawn over time.

The thing to do is monitor indicators to ensure that lubrication is maintained at the correct level. What this looks like will vary be equipment type and cost. Typically monitoring noise\vibration and\or temperatures will suffice, but more detailed monitoring may be desirable.

Any change to the machine operating parameters is a cause for reviewing a possible change in lubrication, i.e., for proper oil viscosity, improving additive technology and required lubrication interval.

We use SOS monitoring for oil analysis and lubricant behavior trends.

Understand the new operating conditions. If the conditions change, the operator needs to understand how the oil will be affected.

Ensuring that load and temperature remain constant. Otherwise, adjusting lube oil selection (viscosity and additives).

This is not consistent across all our sites (I work with several). Some sites are better than others, very dependent upon the individual site’s reliability engineer or designated lubrication program owner (varies by site).

Calculations include operating temperature change. Gear teeth, with proper break in, typically improve lube film over time due to surface burnishing.

Constantly monitor the operating conditions with heat readings, vibration, noise analysis, water ingression.

I review the operating conditions and adjust maintenance as needed.

Generally operating conditions do not change for specific components. If more output is planned, then generally new components are necessary. But rising temperatures might require changes.

Reference to the manufacturer recommendation.

We measure the operation conditions like temperatures, speeds, reductions, metals, etc., and with every change we check if the lubricant is still correct.

We proceed according to the agreed scope of procedures.

Check the OEM specifications, check the lubricant specifications, but mainly rely on oil analysis information. If problems do arise, an STLE Certified Lubrication Specialist™ will be consulted for advice.

Vibration, temperature and noise. Lubricant properties.

It is rare that the changes in operating conditions would be severe enough that they would affect the lubrication. However, when there are changes, the situation is reviewed with the same procedures that would be used in a new machine.

Do you know what the actual lubrication requirements for your machines are?
Yes 86%
No 14%
Based on an informal poll sent to 15,000 TLT readers.
We monitor our lubricating oils and greases more frequently through warmer months.

By reviewing operational data like pressure, temperature, flow and oil analysis.

Consult with my lubricant supplier.

Compare the current operating conditions to the previously documented operating conditions to see if they have changed. Then check if the lubricant will meet the new operating conditions. 

Oil analysis results and temperature measurement.

Need to assess the impact of changed operating conditions on the oil and accordingly select an appropriate oil.

Ensure that the lubricant is a lot more robust and can accommodate for the extreme changes in application.

Use lubrication theory to calculate film thickness and perform analytical investigation of the lubricated components to verify the function of additives (measure wear rates, surface chemical and topographical analysis).

Ensure that the lubricant has the correct viscosity, viscosity index and additive package to manage the change in operating conditions. Close monitoring of in-service fluid analysis is important to identify how the operating conditions changes affect the oil conditions.

It needs to have the correct VI and low temperature properties to service the temperature range of the application.

Laboratory oil analysis and online sensors and dialog with the OEM.

For the biodegradable lubricant, specifications will set and formulating.

Which operating condition changed? The higher the speed, the lower the viscosity. The higher the temperature, the higher the viscosity. The higher the load, the higher the viscosity. Adjust the lubrication parameter in accordance with the operating condition change.

Maximum permissible surface distress.

Have checking the condition of the equipment as part of the maintenance program and documenting any changes to the CMMS.

Take a sample for lab analysis.

My experience has been in the wind power sector of power generation, and the operating conditions change throughout every 24-hour period. The monitoring of the lubricant is monitored for changes in the degradation factors.

1.) Determine the original operating conditions based on the OEM manual. 2.) Then, monitor the operating condition changes. 3.) Conduct continuous oil condition monitoring such as UOA to make sure the lubricant still matches the new operating conditions. 4.) Recalculate lambda ratio; if the drop in lambda ratio is observed, then the viscosity may need to be readjusted. 5.) Change the lubrication properties according to the new conditions. 6.) Change the maintenance interval accordingly.

Checking the technical data sheet of the lubricant and the requirements mentioned by the machine manufacturer. Different temperatures: Using lubricants with a broad operation temperature range, e.g., in hydraulics—high volume low pressure (HVLP) products.

Used oil and condition monitoring. Visual inspections.

Recommended maintenance practice that includes cleaning (if accessible) and relubrication of machine elements.

Editor’s Note: Sounding Board is based on an informal poll sent to 15,000 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.