Machinery Lubrication / Fluid Handling / Oil Analysis

Used-oil analysis: 4 must-dos

Take these steps to optimize your lubrication condition monitoring program.

By Alan Suan, ExxonMobil

It’s no secret that to maximize the reliability and performance of their equipment, operators must be able to effectively understand performance in real time and use equipment insights to further fine-tune and optimize their equipment maintenance program.

One of the most important indicators of equipment performance is lubricant performance. Lubricants are the first line of defense, protecting equipment from an array of challenging operating conditions, such as varying temperatures, heavy loads, and changing speeds.

That’s why understanding lubricant performance is critical. Lubricant condition can change over time, and a high-quality lubricant formulated with the right mix of advanced base oils and robust additives will help mitigate potential equipment challenges such as premature wear, oxidation, and corrosion.

Operators should conduct regular used-oil analysis (UOA) to monitor lubricant performance; this will enable them to identify and address potential performance challenges as they emerge and to further enhance equipment reliability, reduce maintenance costs, and lower the total lifetime cost of equipment ownership.

Effective UOA depends on following some essential best practices, including following sampling best practices and knowing what to look for when analyzing results. Let’s take a look at the four “musts” that will help operators get the most out of their UOA program.

1. What and when to sample - Choose carefully

Oil analysis is effective only when samples are taken from the appropriate equipment at properly scheduled intervals. This is why it’s important to determine what equipment to sample and how often to do so.

Conducting UOA for every piece of plant equipment would be time-consuming and costly, so it’s important to carefully select the equipment that will be regularly monitored, prioritizing equipment that is central to the plant’s overall performance. Generally, operators should consider five general factors:

  • Operating environment. What operating conditions are the equipment subject to, and due to these conditions, how vulnerable is this equipment to potential equipment challenges?
  • Fluid age factor. How has the lubricant performed in service to date?
  • Equipment age factor. How has the equipment performed in service to date, and has it posed any operational challenges in the past?
  • Target sample results. Are the results of any previous oil analysis tests within control limits or above those limits?
  • Economic impact of failure. How vital is this equipment to the productivity and profitability of the broader operation?

Once operators have identified equipment that requires testing, the next step is to determine when samples should be taken. A regular pattern of sampling will establish a credible historical trend of equipment performance. In general, operators should refer to the OEM-recommended sample interval guidelines to ensure accuracy whenever those are available. If operators do not have OEM-recommended guidelines, they can use the general guidelines in Table 1 to help establish initial sample frequency.

2. Take a good (clean and representative) sample

Identifying consistent sampling parameters helps ensure a sound testing methodology, but the accuracy of oil analysis results also depends on an operator’s ability to take a good sample – in other words, a clean and representative sample. Here are a few steps operators should keep in mind to help achieve this.

  • Use a sample port. Sampling location is critical in ensuring you take a good sample. Whenever possible, operators should use sample ports to make it easy and convenient to pull consistent samples. If samples are difficult to pull or require a hand pump, then they might not get pulled frequently. Make sure samples are taken through a sampling valve, vacuum pump, or sampling tube when the equipment is operating at its normal temperature.
  • Establish a regular sampling schedule. A regular sampling schedule will help operators identify trends in lubricant and equipment performance by ensuring that results can be properly compared over time. Integrating the sampling schedule with an operator’s planned maintenance minimizes the frequency of sample pulling and can help deliver this consistency.
  • Take the right precautions. Getting a clean sample requires taking some simple precautions, especially because spotting potential contaminants can be difficult. The laboratory analysis is observing particles in an oil sample less than 8 microns in size; typically these are not visible to the eye (visible particles or water in a sample reflect the possibility of abnormal equipment conditions). As a result, operators should use only new sample bottles and keep lids on until the sample is taken. Before collecting the final sample, rinse and clean the area around the sample port and avoid sampling from the drain plug, where it’s difficult to obtain a representative sample. Flush the new bottle with the oil to be sampled, and do not use degreasing agents to clean sampling equipment, as traces of these substances can affect analysis results. Finally, safety is always a top priority. When analyzing these particles, operators must make sure to wear proper safety equipment.
  • Record equipment and sample details. Trend identification is important to understanding oil analysis results, but identifying trends requires documentation. When submitting a sample, operators should include critical equipment and maintenance information, including date sampled, hours that the oil has been in service, and other relevant information. Collecting this data allows operators to normalize the analysis trends and enhance their assessment of the sample results.

3. Look for the right insights from the oil analysis results

Operators can use UOA results to examine three key areas: equipment condition, lubricant condition, and contamination.

  • Equipment condition. Oil analysis can provide a great deal of insight about equipment condition. Results can reveal metal wear and can help operators understand the metallurgy of the components being tested. For example, metal wear results for a bearing can indicate the relative level of wear for each of the key metal elements in the bearing metallurgy. If caught early enough, maintenance personnel can use these results to address the issue and prevent unscheduled downtime and equipment failure, also resulting in potential cost savings.
  • Lubricant condition. High-quality lubricants must be able to maintain their physical properties to deliver continued protection and extend the equipment’s reliability. UOA results are a critical indicator of lubricant condition, as they may flag abnormalities (see Table 2). For example, if the viscosity of the oil drops significantly, it may indicate a potential equipment performance challenge. In the case of a main gear oil tank, it could indicate that a heater is malfunctioning and cracking the oil, causing viscosity loss, as well as potential oxidation and carbon deposits.
  • Contamination. One of the most important insights offered by used oil analysis results is the presence of contaminants, as contamination is a primary cause of component wear and failure. Three general sources of contamination include: built-in contamination from component manufacturing or the installation process; self-generated contamination from system components worn or damaged by other particles; and external ingression, or contamination from external sources. If contaminants are present, the oil analysis results can help identify the source of the contamination and provide the maintenance team with a better understanding of how to address the challenge. For example, Table 3 lists several examples of contamination and how the presence of those elements can indicate the source of that contamination.

It’s important to note that assessing any analysis data – be it contamination-related or lubricant condition-related – without considering in-service time may lead to inaccurate conclusions about condition severity. Operators should always evaluate data trends relative to wear rate per hour to enhance their assessment. Working with a lubricant supplier can also help deliver the most effective insights, as suppliers can often leverage relationships with equipment builders to help deliver expert insights on specific equipment.

4. Take advantage of new digital technologies to enhance UOA efficiency

Digital technologies have transformed the plant floor for many industrial sectors by increasing efficiency and reducing costs, and the impact of these technologies can have a similar impact for condition monitoring.

Specifically, one of the recent advances in technology is the arrival of mobile-enabled scan-and-go oil analysis platforms that utilize QR-coded labels and mobile and tablet technologies to enable paperless lubricant sampling, thus enhancing process efficiency and the accuracy of results. This scan-and-go technology helps operators prevent transcription errors by allowing them to enter data directly into an online system. The sample’s data packet is then delivered to the analysis partner’s laboratory, and results are delivered back through an online platform. Through this simplification, the process helps reduce the time it takes to conduct the UOA process.

For example, one alumina production plant used this digital UOA platform to enhance efficiency and productivity. This plant typically obtained more than 150 oil analysis samples per month as part of its preventive maintenance program. Each time, the process took more than 24 labor hours per month, with a significant portion of the time dedicated to paperwork.

In an effort to streamline the sampling and labeling process, the plant converted to prelabeled sample bottles with QR codes and a unique number identifier to eliminate time spent during the sample labeling process. As a result, the plant reduced monthly sample collection time by 66% to 8 hours per month, enabling the plant’s maintenance staff to dedicate a significant portion of their time to other activities and see nearly $10,000 in annual cost savings.

Understanding real-time equipment performance is critical to the success of any industrial plant, and this understanding starts with an effective used oil analysis program that can deliver actionable lubricant performance insights. Lubricant suppliers can also help play a critical role in helping in-house maintenance teams conduct these services and interpret results, so operators should seek to take advantage of those partnership opportunities.

By following these four UOA “musts,” plant operators can help ensure that they are getting the most out of their condition monitoring program.