Root cause analysis (RCA) is a tool to address reliability and chronic maintenance problems. It’s a systematic methodology designed to find and deal with sources of problems. That’s why the plant professional needs to understand the role of oil analysis in root cause analysis and in particular, how to use oil analysis to identify causes of accelerated oil degradation.
RCA often is applied improperly in lubrication problems because analysts make assumptions without having supporting technical data. You’ll also need to know the fundamentals of performing a successful root cause analysis with respect to fluid degradation.
The objective of a RCA is to identify what happened, why it happened and what can be done to prevent it from happening again. It involves examining the problem and considering evidence from as many other technologies as possible (Figure 1). Vibration analysis, thermography, ultrasonic analysis, metallurgical analysis, equipment/component inspections and operational data are valuable information sources when investigating a problem.
Fluid degradation can be responsible for many kinds of equipment failure and has a significant effect on an organization’s equipment and component life-cycle, asset utilization, production, safety and environmental costs.
Lubricants are subjected to a range of conditions, including heat, air, incompatible gases, moisture, contamination from dirt and wear particles, process constituents, radiation and inadvertent fluid mixing, that can degrade base oil and additive systems. Viscosity changes and insoluble particulates are among the first of the oil degradation problems to affect equipment performance. Therefore, it’s vital that diagnostic analysis detect these conditions in critical and sensitive lubrication systems.
Rethinking lubricant RCA
The Italian economist Vilfredo Pareto explored the unequal distribution of property, observing that 20% of the people own 80% of the wealth. This relationship is known as Pareto’s Principle and can be applied to countless situations. In equipment reliability, 20% of equipment failures account for 80% of losses.
Therefore, having the knowledge and tools to correct the critical 20% represents a large opportunity for organizations to improve reliability.
Root cause analysis is a term thrown about in lubrication circles on a regular basis. However, in our experience, it’s an instrument that few people use correctly. RCA should be performed on chronic problems or failures that often become more serious over time. Most lubrication-related RCA begins with basic oil analysis and assumptions, which wastes valuable resources. Lack of knowledge doesn’t lead to a failure to identify a root cause correctly. In many cases, the team’s expertise is precisely the problem, as it tends to lead the investigation towards predetermined conclusions. The person or team conduct RCA must possess, among other characteristics, expertise in multiple disciplines, training and experience in RCA, and persistence.
Conducting a successful root cause analysis requires interpreting data logically and investigating without making assumptions. Untenable assumptions and predetermined biases won’t lead to sound conclusions and correct findings.
RCA must start with an understanding of the problem and potential causes. Identify as many potential causes as feasible. Don’t assign blame at this point in the investigation. For each of your potential root causes, construct experiments and tests to confirm your theory’s validity. Keep in mind that data that proves a theory false (the devil’s advocate approach) is important because it can support the correct root cause and helps destroy incorrect assumptions.
Oil analysis can be an excellent tool for fluid degradation RCA. The primary tests for fluid degradation are listed below.
Quantitative spectrophotometric analysis (QSASM) is a laboratory procedure that extracts insoluble contaminants from an oil sample and subjects them to spectral analysis. The color and intensity of the insolubles correlates directly to oil degradation. The test identifies “soft” contaminants (those directly associated with oil degradation) but isn’t strongly influenced by larger, “hard” contaminants unrelated to oil degradation. As a primary test that specifically identifies fluid degradation, QSASM is considered to be highly sensitive and reliable for detecting subtle changes in levels of insolubles.
Fourier-transform infrared analysis (FTIR, or infrared spectroscopy), performed in accordance with ASTM E2412, measures the concentration of organic components. FTIR can monitor additive depletion, organic degradation by-products and the presence of various contaminants. It measures chemistry changes in the fluid base stock in addition to identifying degradation mechanisms.
Ultracentrifuge (UC) sedimentation isolates insolubles by spinning a sample at 20,000 rpm in a centrifuge for 30 minutes. The depth of the separated insolubles is measured visually on a sediment rating scale. The minimum value of 1 represents no to low total insoluble levels. The maximum value of 8 represents a critical level of insolubles. Limitations include the inability to differentiate between degradation by-products and other insoluble contaminants (dirt). The test’s high-g forces also remove additives (VI improvers, dispersants and sulfonates) and it can be labor-intensive to run.
Secondary tests for fluid degradation provide additional data for the RCA analyst:
Viscosity (ASTM D445): Viscosity is the lubricant’s single most important physical property because it is crucial to retaining oil film thickness. It is also sensitive to various forms of fluid degradation -- once degradation causes a meaningful change in viscosity, other indicators (insolubles, acidity and others) already may have been affected, making the viscosity test an excellent secondary tool for monitoring fluid degradation.