Fluid Analysis - Tell the Doctor Where It Hurts

Jack Poley, ALS Staveley Services 

Getting the Most from Your Oil Analysis Program

Fluid [Oil] Analysis, as applied to equipment maintenance and readiness, is essentially an information process, designed to provide the maintenance manager with decision-making data. These data consist of two things: test results and a professional evaluation of those test results.

The oft-used medical analogy to fluid analysis is “blood testing.” This seems perfectly reasonable but it is an incompletely defined analogy. There is a secondary process, the evaluation, usually performed under the same roof as the testing. Evaluation is the rendering of an opinion or advisory, based on current test data and, if available, previous test data from the same system or similar systems. The medical analogy can now be expanded into these two phases by adding the doctor to the definition. When we are examined, our doctor may draw a blood sample and send it to a laboratory. Upon receiving the blood test results he then renders a medical opinion or advisory, which we're free to accept or reject. The doctor, in this instance, is the evaluator.

But there's still something missing from the medical analogy equation–the patient's own assessment of his condition: "I feel 'great', I have severe headaches at night, my shoulder hurts…," etc. Clearly the physician cannot render his best opinion unless he has some idea of the patient's starting point. The notion of patient input relates directly, in the fluid testing arena, to input from personnel at the equipment site: operators, samplers, mechanics, supervisors, OEM technical representatives, oil company representatives, etc. These people all have potential opportunities to impart knowledge to the evaluator who, though having required expertise, may never directly observe the equipment upon whose condition he is opining.

Onsite personnel, therefore, become an extension of eyes and ears for the evaluator. Unless the evaluator is also the sampler with a mechanical background, it is unlikely that he will ever gain such information without the help of others. Here are some important aspects of a sampler's responsibility:

PRIMARY INFORMATION - these are things that simply shouldn't be omitted from a submitted sample.


If the unit is being sampled for the first time, provide the analyzing facility with basic information.

1 UNIT TYPE being sampled, e.g., diesel engine, compressor, hydraulic. This is absolutely minimal information in order to have any chance to process the sample effectively. Note, as well, that even this basic type of identification is potentially fraught with opportunities for mistaken diagnoses. Hydraulic systems, for example, come in numerous strains: axial-piston, vane, and gear for openers. Each of these types of systems has radically different characteristics. How can an evaluator hope to render accurate and useful assessments if he doesn't know whether the blood came from a chimpanzee, an elephant or a human?

2 THE FLUID in the system. OK, this is like asking a patient to provide his own blood type prior to the test, but that's the way the process works. If the testing personnel are not cognizant of the product under test, they could easily fail to set their equipment to properly reference such a product, potentially causing incorrect data to be generated. This, in turn, produces a poor evaluation. Today there are many expert systems in place to minimize such occurrences, but most systems don't possess the sophistication to trap all such possibilities. Further, why make this a guessing game? You're the patient! You have the most at stake.

3 THE APPLICATION in which the unit is engaged. It should be obvious that a hydraulic system exposed to dust and other elements of an off-road application has a totally different environment than one that operates in a relatively clean, protected environment such as a manufacturing plant. Similarly a diesel engine driving a generator operates in a fairly constant-load mode, or similarly consistent, repetitive duty cycle. Contrast this application to a similar diesel engine operating as the power plant for a public bus, where the duty cycle is varied and not always conducive to best performance and component life.

Once the unit has been registered or previously sampled…

1. Unless bar coding is available, provide complete and consistent component identification on the sample container's label. This includes understanding that any change in the way equipment identification or designation occurs can cause additional history records to be generated when, in fact, the test results should have been appended to a previous record.

2. Accurately record the time on the fluid since it was last changed. Clearly, wear and contamination ingestion rates, as well as additive effectiveness–if part of the lube analysis strategy–cannot be fully evaluated without this information.

3. Accurately record the time since the unit was placed in service, or since last overhaul–new units may tend to produce slightly higher metals and contamination values for various reasons such as wear-in or conforming processes. Conversely, old units tend to show varying traits from 'better' wear rates (excess lube consumption) to accelerated wear rates (the beginning of the end of the life cycle).

4. Provide the date upon which the sample was extracted–someday you may wish to have your units placed into a database of your choosing, and you will appreciate having the samples in chronological order for your statistical analysis requirements.

All of the above is intuitive and obvious to the reader. So why is it presented at this mature time in the evolution of the fluid analysis process? Because it has not been fully implemented in the sampling communities. Because, perhaps, over half of the samples routinely processed do not contain this information on any sort of consistent or complete basis. It is the equivalent of going to your doctor for your checkup but, instead of advising him how you feel, you state: "That's what I came here for you to tell me". Previously, as well, you would have omitted key information when you filled out the patient form upon registering in the reception room. Granted equipment health does not approach the urgency of human health, but it does relate to money and utilization. Since that's why the fluid analysis process exists, why not maximize the return on the investment?

Event specific information makes choice of alternate tests and subsequent evaluation much more effective. Condition examples that could trigger such tests include: Abnormal lube consumption–as previously noted, fresh oil makeup, dilutes, metals and contaminants test values. These data can be “normalized” if lube consumption information is available.

Macro observations about the equipment's operation:

1. Unusual noises - gear pitch whining, grating, change in overall pitch, pinging in combustion engines, bearing or
piston knock, etc.

2. Lack of power - primarily an engine aspect

3. Smoke - amount, color, when observed in the duty cycle

4. Oil leaks - gasket or seal impairment

5. Filter condition as observed with unaided eyes, upon removal

6. Changes in performance, such as output level, quality, etc.

If one accepts the previous claim that most people doing the sampling don't provide even primary data for lube samples on a consistent basis, it isn't hard to leap to the conclusion that secondary information is even less routinely available. The unfortunate issue here is that lack of primary information, while important, is not nearly as important and consequential as lack of secondary information for those units which may experience problems. When one makes a decision to interrupt a piece of equipment's service and perform significant diagnostic and maintenance procedures, especially including visual inspection via teardown, it is vital to have as much confidence in this decision as possible. While hardly an all-inclusive list, the importance of above items to the diagnostic process should be clear.

This then leads to the final link in the information chain:


In completing the process, collateral diagnostic information may be critical to the ultimate assessment of machine and oil.

Diagnostics or maintenance performed since the unit was previously sampled, including the findings and/or corrective action, and whether or not a this resulted from a routinely scheduled procedure, or the result of an exceptional observation, or from the lube analysis itself.

Other condition monitoring observations from vibration analysis, thermography, motor current evaluation, etc. Parts replacement or overhaul and, if possible, a description of the visual condition of the unit and its respective parts upon such replacement/overhaul.

Again, it is obvious that such information can only serve to greatly improve the accuracy of the test results' implications, both for the specific sample at hand, and for future diagnoses when similar conditions and results arise.

One can never have too much information when evaluating test results on a fluid sample. The process is a partnership in dynamic and interactive information dialog, as opposed to a one-way communication. Those submitting samples for testing/evaluation have a responsibility to provide as much relevant information as possible, particularly when such information is exceptional or telling, if best results are to be expected and obtained.

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