Lube Oil Sampling and Testing Flashcards
Oil analysis
Routine activity for analyzing oil health, contamination and machine wear. Purpose: to verify that a machine is operating properly. Oil analysis shows the condition of the oil and gives an idea of the condition of the machine from which the sample was taken.
Abnormal conditions can be identified through oil analysis, immediate actions can be taken to correct either the root cause or mitigate an oncoming failure.
Oil analysis can be compared to blood analysis for the human body. For machinery, we can determine if any actions should be taken to keep the machine healthy and to extend the life of the oil.
What are the 3 main categories of oil analysis?
- Fluid Properties
- Contamination
- Wear Debris
- Fluid properties
Focus on identifying the oil’s current physical and chemical state and defining the remaining useful life (RUL).
a) Does the sample match the specified oil identification?
b) Is it the correct oil to use?
c) Are the right additives active?
d) Have additives depleted?
e) Has the viscosity shifted from the expected viscosity? If so, why?
f) What is the oil’s RUL?
- Contamination
Detecting the presence of contamination and narrowing down their probable sources.
a) Is the oil clean?
b) What types of contaminants are in the oil?
c) Where are contaminants originating?
d) Are there signs of other types of lubricants?
e) Is there any sign of internal leakage?
- Wear Debris
Determine the presence and identification of particles produced as a result of mechanical wear or corrosion.
a) Is the machine degrading abnormally?
b) Is wear debris produced?
c) From which internal components is the wear likely originating?
d) What is the wear mode and cause?
e) How severe is the wear condition?
Details to provide when sampling
a. The machine’s environmental conditions (extreme temperatures, high humidity, high vibration, etc)
b. The originating component (steam turbine, pump, etc), make, model and oil type currently in use
c. The permanent component ID and exact sample port location
d. Occurrences of oil changes or makeup oil added, as well as the quantity of makeup oil since the last oil change
e. Whether filer carts have been in use between oil samples
f. Total operating time on the sampled component since it was purchased or overhauled
g. Total runtime on the oil since the last change
h. Any other unusual or noteworthy activity involving the machine that could influence changes to the lubricant
Equipment failure
The eventual failure of a piece of equipment is inevitable. Wear and tear naturally occur with continual usage and equipment will ultimately reach a functional failure point.
The P-F curve
Way of representing machine behavior or condition before it has reached a failed state and illustrates a machine’s progression towards failure.
x-axis is time to failure (starting from installation), y-axis represents a machine or component’s resistance to failure
Represents a concept only and does not have units or scale.
Potential failure (P) - detectable state of failure or the point at which degradation begins
Functional failure (F) - reached a failed state or no longer performs satisfactorily
P-F interval
Represents the time between when potential failure is detected and when it reaches the failed state. The length of the PF interval is largely determined by the method used to detect failure.
The method and frequency of detection determines the length of the PF interval. The more often machines are inspected (and more detailed the method), the more time there will be between detection of potential failure and when failure takes place. Advanced condition monitoring techniques will show potential failure long before you can hear/feel/see it.
Maintenance
- Predictive maintenance: done to determine the current running condition and give a prediction of what’s going on and if there are potential failures
- Preventative maintenance: carried out as per manufacturer’s instructions or best practices
- Reactive maintenance: performed when the machine is exhibiting signs of imminent failure
- Predictive maintenance
Uses condition-monitoring tools or techniques to monitor the performance of a piece of equipment during operation. Uses tests and sensors to record a wide range of data (temperature, pressure, vibration) from the physical actions of a machine and the recorded information enable someone to predict the future failure point of the machine being monitored. Allows for the machine to be fixed or replaced just before it fails.
Testing:
Lubricating oil analysis
Vibration analysis
IR Thermography
- Preventative maintenance
Inspecting and performing maintenance at predetermined intervals, whether or not it is required. Maintenance intervals are typically based on either usage or time.
- Reactive maintenance
Responding to equipment malfunctions or breakdowns after they occur in order to restore the machine to normal operating conditions.
a. Breakdown maintenance: completely broken and may require extensive repairs (or replacement) to run again
b. Run-to-failure maintenance: deliberately run until it breaks down. After failure, reactive maintenance is performed - no prior or preventative maintenance is performed in advance
c. Corrective maintenance: targets and repairs a system malfunction so that the machine can be restored to proper working order
d. Emergency maintenance: last-minute response to the sudden breakdown of a machine that would become a threat to health and safety if not repaired. Entails some type of threat to health and safety.
Suitable approaches
In some systems, reactive maintenance may be a suitable approach, but if the machine is part of a critical system, the vessel will be out of service (undesirable) until the problem can be fixed.
Preventative maintenance is important but it must be scheduled around operations and costs a lot to carry out.
Predictive maintenance allows the maintenance frequency to be much lower, while still preventing unplanned reactive maintenance, minimizing downtime and costs associated with preventative maintenance.
In reality, use a combination of predictive, preventative, and reactive maintenance.
Implication of lube oil analysis
Lube oil analysis. along with predictive maintenance procedures, is a key component of keeping the vessel and associated equipment running properly and safely by detecting a potential failure long before it may seriously damage a machine and cause failure.
Lube oil testing (examples)
- Basic Spectrographic Oil Analysis
- Particle count analysis
- Neutralization number
- Allowable soot test
- Viscosity test
- Filter analysis
- Basic Spectrographic Oil Analysis
Identify the following conditions and compare to a base line (new oil)
- Presence of wear metals
- Presence of contaminant metals
- Base elements
- Viscosity/grade of the lubricant
- % of allowable soot
- % of allowable sulfur
- % of allowable oxidation
- % of water
- % of glycol
- Fuel dilution
- Flash point
- Particle count analysis (ISO 4406)
Lubricant cleanliness is key to increasing component life, increasing lubricant life and reducing costly routine maintenance. Clean, dry lubricants will improve machine performance and longevity.
Small particles cause abrasion wear. Large particles cause fatigue wear. Particles in the lubricant will increase lubricant degradation rates. Particles in hydraulic control systems will degrade hydraulic functions or even cause performance failures. Particles in other hydraulic systems will cause abrasion wear and hydraulic leaks. In extreme causes, particles can partially clog oil ports and result in lubricant starvation to vital machine components.
Test is performed using an automatic laser light particle counting instrument. A laser light beam is shown through a constant flow rate stream of oil. As particles entrained in the oil pass through the light beam, the attenuation of the transmitted light as seen by a sensor is measured versus time. Using the flow rate and the attenuation versus time curve, particle size can be determined and counted. The number of counts for a given size ranges are then classified according to an ISO 4406 standard.
While particle count analysis will not indicate what the particles are, it will indicate the need for further analysis, usually microscopic particle analysis, to determine not only what the particles are, but to help determine where they came from, how to clean up the lubricant and how to prevent them from reoccurring.
- Neutralization number
As lubricants degrade from oxidization, they form a number of acids. These acids are corrosive to many metals and if left uncorrected for a period of time, will begin to cause corrosion and possibly eventual bearing failure. Neutralization number is composed of the TBN and TAN and evaluate the quality of the oil that remains in service. Must always be compared to a datum taken from a new clean sample of oil.
Total Acid Number (TAN): used to determine the amount of acid formed in the oil. Standard neutralization number test for industrial lubricating oils. Performed by titrating a solution of oil and diluent with an alcohol/potassium hydroxide solution (a base) until all the acids present are neutralized. The results are reported as milligrams of potassium-hydroxide per gram of sample. A small increase in TAN usually indicates oxidization and lubricant degradation, contaminants with acidic constituents can also be a factor. When a lubricant’s acid number reaches a condemning limit, replacement or sweetening is the best option
Total Base Number (TBN) used to determine the oil’s ability to neutralize acids that are formed during combustion. Standard test for engine lubricants. Measurement of the amount of protection in the lubricant remaining to neutralize acids formed as a result of combustion. A solution of oil and diluent is titrated with an alcohol/Hydrochloric acid solution until all the alkaline or base constituents in the oil are neutralized. Results are reported as milligrams of hydrochloric acid per gram of sample. When TBN of the oil reaches 50% of the value of new oil, time to change the oil.
- Allowable soot test
Used when analyzing oils from internal combustion engines (mainly diesel), conducted to see how much soot (carbon by product of combustion ) has accumulated in the oil
- Viscosity test
Used to determine the current viscosity of the oil and to evaluate the performance of the oil. An increase in viscosity will indicate that the oil has deteriorated through oxidization. A decrease in viscosity usually indicates fuel dilution, contamination, or that the oil has broken down due to shear.
- Filter analysis
In pressurized lubricant systems, proper maintenance and sizing of filters are essential to maintaining lubricant cleanliness. In failure events, the history of that failure is often contained in the filter. Significant or sudden changes in the differential pressure across the filter usually indicate a wear or contaminant event. To determine the severity of the event, the filter should be submitted for analysis.
Submitted filters are first dissected and the filter media is examined for degradation. Particles from the filter are removed through backwashing and/or ultrasonic cleansing and analyzed. The particulates removed are also examined microscopically. Moisture and acid content are also determined. Organic contaminants present in the filter can also be analysed.
Lube Oil Sampling
Proper sampling is a critical part of an effective oil analysis program.
3 primary goals when taking samples:
1. Maximize data density
2. Minimize data disturbances
3. Proper frequency
The sampling location, device and procedure should be consistent. The steps taken should be well documented so that they can be followed by anyone delegated to take a sample.
- Maximize data density
Any oil sample should be fully analyzed to ensure that you obtain the most information possible on the oils condition (viscosity, depletion of additives, presence of wear particles)
- Minimize data disturbances
Every sample taken should be taken the same way. Sampling procedures should be simple and set up so that the sample does not become contaminated during the sampling process, as this can distort and disturb the data
- Proper frequency
Samples should be regularly taken so that any potential problems with the oil can be detected early.
Location of sampling points - Pressurized systems
Samples are taken downstream of the equipment after it has completed its primary functions and during typical working conditions. Location of the sampling point is key to getting a good representative sample from a machine, but the location will change depending on the type of system.
Rules of thumb for properly locating oil samplings ports on pressurized circulating systems
- Turbulence
- Ingression Points
- Filtration
- Drain lines
- Turbulence
The best sampling locations are highly turbulent areas where the oil is not flowing in a straight line but is turning and rolling in the pipe. Should not be located at right angles to the flow path as this can lead to a substantial reduction of the particle concentration entering the sample bottle. Should be located at elbows and sharp bends in the flow line.
- Ingression Points
Where possible, sampling ports should be located downstream of the components that wear. A sample taken from a return line or drain line heading back to the oil reservoir offers the best chance of determining what wear debris and contaminants are in the oil
- Filtration
Properly functioning filters will remove most if not all contaminants so they remove valuable data from the oil sample. Sampling points should be located upstream of any filter (unless the performance of the filter is being specifically evaluated)
- Drain lines
In drain lines where oil may be mixed with air, sampling points should be located where oil will travel and collect. On horizontal piping, this will be on the underside of the pipe. On lube oil systems where there is a specific return line or drain line back to a reservoir, this would be the best place from which to sample. This allows the sample to be taken before the oil returns to the tank. If the oil is permitted to return to the tank, then the information in the sample becomes ??? and any debris in the reservoir tends to accumulate over weeks and months and may not accurately represent the current condition of the machine.
Live Zone Sampling Procedures
- Portable high-pressure tap sampling
- Minimess tap sampling
- Ball valve tap sampling
- Portable minimess tap sampling
- Sampling from sumps
- Portable high-pressure tap sampling
A ball valve or needle valve is installed in a high pressure zone and the outlet is fitted with a piece of stainless steel tubing. The purpose of the tubing is to reduce the pressure of the fluid to a safe level before it enters the sampling bottle.
- Minimess tap sampling
A connection that allows for live zone sampling from return lines or from high pressure hydraulic lines. The valve is connected into the lube oil system (preferably at an elbow) and has a mechanical check valve (spring loaded ball) fitted inside. Plastic tube is attached to a special adaptor and when the adaptor is pressed into the valve, it unseats the ball and oil flows into a sample bottle. This method is safe for use on high pressure lube oil systems carrying hot oil.
- Ball valve tap sampling
A ball valve is installed on an elbow. The valve is first opened so that it can be flushed of any debris/contamination. Once flushed a sample bottle is held under the valve and filled. The main drawback of this method is that there is a high risk of contaminating the sample and it is not suitable for high pressure applications.
- Portable minimess tap sampling
Same as the minimess tap sampling but the sample valve is fitted to a quick connect fitting. A corresponding fitting is placed at the sample point and when the two are connected together, it provides a safe method of obtaining a sample. This method is only common on high pressure hydraulic systems.
Note: occassionally, a line is not sufficiently pressurized to take a sample. In these instances, a special vacuum pump will be used. The sample bottle is connected to the pump and the pump is connected to a minimess valve. When the vacuum pump is operated, a sample is drawn into the bottle.
- Sampling from sumps
A lube oil sump is a reservoir below a machine where oil is collected to be reused. In many machines having lube oil sumps, a return line cannot be accessed or does not exist. In these machines, fluid must be samples from a pressurized supply line leading to the bearings or gears and located between the lube oil pump and the filter. In some machines, a system is fitted to remove oil from the sump, filter it and send it back to the pump. This is referred to as bypass filtration and provides an ideal location to install a sampling point between the pump and filter. A ball valve or minimess valve will be used since the fluid is under pressure.
Location of sampling points - Non-pressurized systems
In some machines (e.g. winch gearboxes) there isn’t a pressurized lubrication system. Oil is contained in the sump and lubrication is done by either the bearing being immersed in the oil or the oil will be sprayed (splashed) into the bearing by either the gears or a ring fitted to the shaft. In these machines, collecting a good, consistent lube oil sample can be a challenge.
1. Drain plug
2. Drain port sampling
3. Drain port vacuum sampling
4. Drop tube vacuum sampling
- Drain plug
The most basic method for obtaining samples from these machines is to remove the drain plug from the bottom of the sump, allowing fluid to flow into the sample bottle. For many reasons, this is not an ideal sampling method or location. Sediment, debris and particles (including water) will settle in the bottom of the sump and enter the bottle in concentrations that are not representative of what is experiences near or around where the oil lubricates the machine. Sampling from the drain plug should be avoided if at all possible.
- Drain port sampling
Greatly improved sampling. A short length of pipe or tubing extends inward and up into the active moving zone of the sump. A ball valve is fitted to the end of the pipe and a sample is drawn as needed. Ideally the end of the tube, where the oil sample is taken from, should be halfway up the oil level, 2 inches in from the walls and at least 2 inches from the rotating elements within the sump.
- Drain port vacuum sampling
A minimess valve is installed in the drain port but instead of fluid passing into a sample bottle by gravity, it is assisted by a vacuum sampler. This is particularly helpful where the oil is viscous and difficult to sample through a narrow tube.
- Drop tube vacuum sampling
One of the most common methods for drawing a sample from a sump. A tube is inserted through a fill port or dip stick port and lowered into the sump cavity, usually about midway into the oil lever. A vacuum pump is used to draw up oil to the sample bottle. Considered a method of last return.
- Drop tube vacuum sampling : risks & problems
- Tube location: a tube that is directed into the fill or dipstick port is extremely difficult to control and the tube’s final resting place is hard to predict. This results in samples being taken from different locations each time. There is also a risk of the tube actually going all the way to the bottom of the sump where debris and sediment are picked up.
- Drop tube contamination: when the tube is being inserted into the sump, it will scoop up debris from the sides of the pipe
- Large flush volume: increases the volume of fluid that must be flushed in order to obtain a representative sample. For some small sump systems, this practically results in an oil change. In addition, if the removed volume of fluid is not replaced, the machine might be restarted without an adequate oil volume
- Particle fallout: for most systems, a shutdown is required to deploy this method. As well, particles begin to settle and stratify according to size and density immediately upon shutdown, compromising the quality of the oil analysis.
- Machine intrusion: the machine must be entered to draw a sample. This introduced the risk of contamination, and there is always the concern that the machine might not be properly restores to run-ready condition before startup.
Sample Bottles and Hardware
An important factor in obtaining a representative sample is to make sure the sampling hardware is completely flushed prior to obtaining a sample. This is usually accomplished using a spare bottle to catch the purged fluid. It is important to flush 5-10 times the dead space volume before obtaining the sample.
There is an assortment of sampling bottles that are commonly used in oil analysis, most often supplied by the company that will be performing the analysis. Sample bottles vary from 50mL to a more common 100-120 mL. The larger bottle is preferred when tests such as particle count and viscosity analysis are required. If a considerable number of different tests are required, a 200 mL (or 2x 100mL) bottle may be required. It is important to ensure that the bottle size will provide sufficient volume of sample to conduct all the required tests and leave some extra for storage in case a rerun is necessary.
The entire volume of the bottle should not be filled with fluid during the sampling process, only a portion of the bottle should be filled. The unfilled portion, called the ullage, is needed to allow proper fluid agitation by the laboratory to restore even distribution of suspended particles and water in the sample.
Bottles are available in either plastic or glass, and clear plastic tubing is commonly used for taking samples. Note: only clean new bottles and tubing should be used for each sample.
Points to remember
- Machines should be running at load during sampling. Samples should be collected when machines are at normal operating temperatures, loads, pressures, and speeds on a typical day
- Always sample upstream of filters and downstream of machine components such as bearings, gears, pistons, cams, etc. This ensures that no data (such as particles) is being removed by filters or separators.
- Create specific written procedures for each system samples. This ensures that each sample is extracted in a consistent manner.
- Ensure that sampling valves and sampling devices are thoroughly flushed prior to taking the sample. Vacuum samplers and probe-on samplers should be flushed as well.
- Make sure that samples are taken at proper frequencies and that the frequency is sufficient to identify common and important problems. When sending off a sample indicate the machine and type of oil. Record machine hours, hours on the oil, hours since last oil change, and how much oil was added since the last sampling period.
- Forward samples as soon as possible to the oil analysis lab after sampling. The properties of the oil in the bottle and the oil in the machine begin to drift apart the moment after the sample is drawn.
