We have always stressed the importance of proper sampling techniques to the accuracy of oil analysis results and machine diagnostics program. The same can be said for choosing the right oil analysis test slates or parameters. When you avail of oil analysis test packages, the tests must be designed according to the failure modes you are diagnosing and the requirements of the equipment.
How do you determine a good oil analysis test package? A good oil analysis test package should be able to capture the three aspects of the lubricant and machine: oil properties condition, contamination condition, and machine wear condition.
Fluid Properties Condition
Test parameters that reveal fluid properties are perhaps the most common tests which reliability engineers are most familiar with, one of which is viscosity. Viscosity stability is crucial to the health of the machine as it protects components from metal-to-metal contact. Other tests are acid or base number, additive levels, nitration, and oxidation.
According to the Pareto Principle, contamination is one of the key causes of 80% of machine failure. Contamination can take the form of solid contaminants which are quantified by using particle counting and ISO 4406:99 code. Meanwhile, moisture contamination is reported in parts per million (ppm).
When availing of contamination test slates you should talk to your third-party laboratory to set up your target cleanliness and your third-party laboratory partner should be able to adjust them according to your need. If you don’t know how to start, you can discuss your challenges and what you plan to achieve so that they can come up with the best target limit for you.
Machine Wear Debris
When machine failure is in its early stage, a certain amount of machine wear is generated but as the failure progresses, the size of machine wear grows bigger. To be able to fully assess the degree of severity of wearing, fine wear and coarse wear must be both measured.
Important Test Slates for Every Machine Application
If you are doing routine oil analysis testing, then, well and good. Check your current test parameters if they include the following test slates per application:
With diesel engines that have hundreds of moving parts, it is important to measure and manage contaminants such as coolant, fuel, and excessive soot loading. Engine typically requires oil that is high in additive content. Because fuel combustion is part of its process, which produces carbon dioxide, it makes sense to monitor its level of additives using total base number (TBN).
Majority of hydraulic failure is caused by particle contamination which often leads to pump, cylinder, valve issues. For this reason, we strongly recommend that hydraulic test slates should always have particle counting and moisture test. Varnish formation is another inevitable byproduct of hydraulic oil degradation. Varnish needs to be routinely measured using Varnish Potential Testing.
Industrial gearboxes oftentimes encounter issues such as misalignment, overloading, lubricant starvation, and improper lubrication. The test slates you choose should be able to help you conduct failure modes and effects analysis (FMEA). For incipient failure due to machine wear debris formation, it is vital to measure both fine and coarse wear. These tests can be further supported by analytical ferrography for better root cause analysis.
Motor and Pump Bearings
The focus of a proactive machine diagnostic program for motor and pump bearing should be on oil condition and cleanliness since they operate at high speeds. Just like hydraulic systems, motor and pump bearings also require elemental analysis.
Steam and Gas Turbines
Steam turbines use large volumes of oil which requires regular monitoring to plan for oil sweetening. To monitor lube oil condition, include viscosity, total acid number (TAN), nitration, oxidation, remaining useful life evaluation routine (RULER), and RPVOT. Other key tests that are crucial to the condition monitoring of turbines are contamination, foam, air release, demulsibility, rust prevention, and corrosion.
There is a wide range of compressors from reciprocating to rotary for compressing air and process gases. Thus, their oil test slates also vary. For screw-type compressors where there is a mixing of gas and lubricant which makes oil oxidation a possibility, test slates should include viscosity, acid number, and oil condition. Cleanliness is also critical to the smooth operation of compressors. Compressors that are used to compress liquids and gases that are flammable may require flash point testing.
Oil Analysis Interpretation
Choosing an oil test slate is critical to the success of your oil analysis program and oil analysis interpretation. If your oil test slates are too limited or not sensitive enough, you may not be able to catch the problem right on time before the problem turns catastrophic. Remember that the real value of an oil analysis report lies in its accurate data and ability to give you an explanation on the root cause of machine and lubricant problems.