Oil-Analysis Data Evaluation
EP Editorial Staff | January 1, 2010
Until you understand what you’re looking at and looking for, you’re no better off than before you implemented your oil-analysis program.
My last article discussed the importance of implementing an oil-analysis program and some strategies for building one that’s top-notch (“Developing An Effective Oil-Analysis Program,”). Previous articles had covered proper sampling techniques and the relevant tests used in oil analysis. This article focuses on understanding and applying the data generated by an oil-analysis report in order to identify potential problems and be able to take corrective actions before a serious situation develops. Emphasis here will be on industrial applications only, NOT on mobile equipment where oil analysis is also used extensively. Incorporating actual data from a plant, key factors (by equipment type) that need to be considered when evaluating an oil-analysis report will be noted.
Oil analysis can be likened to a blood test during an annual physical. A blood test provides important information on a person’s health; oil analysis supplies vital information on the health of your machinery. None of this information, however, is of any value unless you are able to understand and apply the data contained in the reports generated by these analyses. The following details will help you do so.
Although oil-analysis laboratories may use a variety of report styles, there are many similarities in how the data is reported.
Oil analysis looks at two primary oil conditions that could cause equipment problems.
- Chemistry changes can be caused by the oxidation or thermal degradation of the oil. This is usually detected by measuring the acid number and the oil viscosity.
- Contamination, primarily from particle or water ingression, can dramatically affect equipment life. Addition of the wrong oil is also a form of contamination. Primary tests to measure contamination are particle counts for solid components and Karl Fischer for water. Atomic emission spectroscopy (AES) detects metallic contaminants such as dirt ingression by measuring the silicon level and changes in metallic additive levels, which may indicate lube mixing.
The report is broken down into two major components:
- Sample/equipment information is at the top of the report. It includes all pertinent information on the sample and the equipment type. This information is on every report and is developed from details the user provides to the laboratory when filling out the equipment form. Furnishing complete information will aid in identifying problems and making meaningful recommendations.
- Test results are presented in the body of the report. Recommendations, when needed, are either at the top after the equipment section or at the bottom of the report.
- Most reports list the data horizontally by date, with the latest on either the top or bottom. (Some labs may list their data vertically, with the latest on the left.)
- Emission spectroscopy (usually located right after the sample/equipment section) is separated into three groups: wear metals, additives and contaminants. It’s a crucial part of any oil-analysis report measuring metallic elements in ppm (parts per million), but only particles <10 micron are detected. Thus, additional techniques are needed to measure large wear particles.
- Physical tests for oil condition and contamination are usually near the bottom of the report. These include tests for viscosity, water, acid number, FTIR (Fourier Transform Infrared), particle counts and ferrous density. Analytical ferrography is on a separate page.
- The sample report in Fig. 2 also lists the new oil reference sample to compare with the used oil. Many labs don’t report this data, which gives good insight on the condition of used oil. New oil reference samples should be updated yearly.
- Oil analysis reports include a severity rating. Most companies have a two tier code: abnormal or caution and critical or warning. One laboratory has a four tier severity code from 1-4. The data in the report is color coded to reflect the severity. Most companies use red for critical.
- The report in Fig. 2 includes the lab’s watch and warning limits. (Most laboratories don’t include this information.)
As noted here, the following factors, per specific equipment type, reflect how oil-analysis data can be used relative to problem identification.
- Cleanliness is a key component in smooth operation. Thus, particle counts should be closely monitored.
- Pump wear is not a common problem and is usually exhibited through increased copper levels resulting from wear of slipper shoes, swash plate and pressure plates.
- Aluminum occurs in gear pumps from housing wear.
- Iron/chrome indicate the presence of cylinder rod wear, usually from abrasive particles.
Information in Table I comes from an actual oil-analysis report. Only pertinent data from the report is presented.
This report indicates sudden high iron and copper wear for a hydraulic system. The copper could be coming from the pump and the iron/chromium indicates cylinder rod wear. (The particle count increased as a result of abrasive particles being introduced into the system; these particles caused the wear.) Further investigation with analytical ferrography was conducted to identify the wear mode and types of particles present. The results showed the presence of the following:
- Excessive siliceous, iron oxide and nonmetallic debris
- Cutting wear particles, indicating severe abrasion wear
- Excessive amounts of large fibrous masses consisting of cellulous and synthetic glass fibers.
The sudden increase in particles was linked to the sudden increase in wear. Analytical ferrography concluded that the particles came from a sudden filter rupture releasing a large number of abrasive particles into the system. (This was confirmed when the system was checked and the filter rupture was found. Whenever there is a large increase in particle counts, the filter integrity should be checked.)
Steam/Gas Turbine Equipment…
Wear metals are not common and are flagged at very low levels. Many systems have large fluid reservoirs, and even a small amount of metallic wear can indicate a serious problem.
- Turbine oils normally contain no metallic additives. Any presence of metallic additives usually indicates lube mixing. For example, if zinc and phosphorous are found in turbine oil it indicates the addition of hydraulic oil. Some turbine oils may contain phosphorous as an antiwear package. Be sure to run a new oil reference on your oil to see what additives are present.
- Turbine oils are in systems for extended periods (especially steam-turbine oils). Other non-routine tests, such as RPVOT (Rotating Pressure Vessel Oxidation Test), water separability, etc. are conducted periodically to determine their condition.
- A major problem with steam-turbine oils is water incursion through a steam leak. Water levels should be closely watched in turbine oils—and kept below 200 ppm.
- Varnishing in gas turbines has become a major issue and many oil-analysis laboratories have developed extensive testing packages to measure the varnish potential of the oil. Discussion of these tests is beyond the scope of this article.
The report reflected in Table II notes several serious problems:
- High iron wear
- High tin wear along with copper wear, indicating the wiping of a Babbitted bearing
- Viscosity increase of 15% over new oil reference
- High level of water ingression at 1220 ppm
Additional tests performed with the use of analytical ferrography indicated the following results:
- Large number of red oxides signifying rust through water incursion
- Large number of siliceous particles
- High alloy steel particles indicating shaft wear
- A few large Babbitt particles and a large number of smaller ones
A serious condition existed due to higher-than-normal wear caused by steam incursion into the bearing housing. The introduction of water and particles resulted in Babbitted bearing wear and corrosion. Find source of steam incursion and repair. Consider changing oil because the high acid number along with viscosity increase signifies oil is becoming highly oxidized. If oil is not changed, remove water through vacuum dehydration. (In this case, the oil was changed and the steam leakage problem resolved. No further problems were experienced.)
Stationary Enclosed Gearboxes…
- High iron wear—usually around 100 ppm—is common in gearboxes and varies by type and manufacturer. Oil-analysis labs are able to establish more accurate condemning limits if they are provided with complete information, such as type, OEM, model number, sump capacity and filtration, if any, on the gearbox being analyzed.
- DR (Direct Reading Ferrograph) and PQ (Particle Quantifier) tests are typically used to measure ferrous density and should be considered routine for unfiltered gearboxes.
- High copper levels are common for worm gears because the yellow metal ring gears are sacrificial.
- Analytical ferrography is a valuable test to use for the prevention of major gear failures.
- Typical EP gear oils have 300-350-ppm of phosphorous.
This report indicates the onset of severe wear as evidenced by the large jump in FDRL (which measures ferrous particles > 5 microns). Analytical ferrography results indicated the following:
- Heavy accumulation of carbon steel wear particles
- Large striated gear wear detected, indicating severe root/tip sliding wear
- Large carbon steel particles, which were indicative of heavy pitch-line fatigue
- Excessive number of copper particles indicating heavy bearing/cage wear
Severe gear and bearing wear is occurring and will lead to an impending failure unless corrected.
(It actually turned out that portions of the gearbox had to be replaced, but the problem was identified early enough to order the parts and install with minimal downtime. A sudden failure would have resulted in a minimum of six weeks downtime and much higher repair costs. The problem was identifying the root cause in this large heavily loaded gearbox. No problem was initially identified with the lubricant. Viscosity, acid number and contaminants were all normal. Consequently, it was assumed the problem was mechanical—but this was not found during the repair process. Upon further investigation, it was determined that the OEM recommended the wrong viscosity oil. The initial recommendation of an ISO 220 was too low for the speed and load conditions. The EP package of the oil, with 100 ppm of phosporous, also seemed low. The gearbox was repaired and ISO 320 EP oil was used, resulting in no further problems.)
The ability to read and understand an oil-analysis report is vital for making decisions on your equipment. Don’t depend entirely on your oil-analysis lab for recommendations. You know your equipment and its history better than a lab does. There can be a great discrepancy among the laboratories when it comes to recommendations. Because of the large number of samples analyzed daily, their recommendations are exception-driven by a computer. Some labs have analysts who look at the exception data and make the recommendations. Many reports will simply recommend that the oil should be changed—which, in many cases, doesn’t address the root cause problem.
The more knowledgeable you are in understanding the data in your report as it relates to your equipment, the easier it is to work with an oil-analysis technical expert. You know your equipment and he/she knows testing. Together, you can come up with the right solution to the problem.
Here are several key points to keep in mind:
- Most reports will not show any exceptions. Review reports based on the criticality assigned to the report by the laboratory. Study all reports that show some abnormality. Call your laboratory for clarification of critical warnings you receive.
- When an action step is recommended relative to a problem, rectify that problem as soon as possible. Many a catastrophic situation has developed as a result of the corrective action step(s) recommended by a laboratory not being taken in a timely manner.
- If a critical situation develops with no warning, resend the sample for testing. Don’t base a major equipment decision on one sample point.
- Lube mixing is a common problem. You need to send in a new oil reference yearly to get meaningful comparisons on the condition of the used oil. Look at the viscosity and metallic additives to identify lube mixing.
- Finally, work closely with other condition-monitoring specialists (i.e., vibration analysts) in your plant to confirm potential problems. LMT
Contributing Editor Ray Thibault is based in Cypress (Houston), TX. An STLE-Certified Lubrication Specialist and Oil Monitoring Analyst, he conducts extensive training in a number of industries. Telephone: (281) 257-1526; e-mail: email@example.com