What is Oil Analysis?
In this article I’ll be running through the basic benefits of carrying out a regular oil sampling and analysis programme. looking at who needs it, who should be carrying out the work, what types of machines is it suitable for, why even small units will be suitable and the reasons why.
Who needs oil analysis?
I suppose the first question that gets asked is “Who needs an Oil Sampling and Analysis Programme?” and a common thought is “Surely this is only applicable to those places where huge machines are involved.”
So firstly, any company using machinery which contains components which are lubricated is a suitable candidate. In this instance size isn’t really that important, providing a sample which is capable of being analysed can be obtained, in reality 60ml for most oil tests and a few grams for greases.
Who should carry out the Sample collection?
The actual sampling needs to be carried out by someone who has been trained in the correct procedures which should be observed and complied with. This is necessary in order to prevent damaging the unit from which the sample is being taken or creating a non-representative sample during the collection phase of the process by failing to take the necessary precautions to prevent the ingress of external contamination.
What sort of machines should we have Oil Analysis carried out on?
In reality there is no reason to think that Oil Analysis is only suitable for a ‘specific’ range of industries or to those who only have assets which contain large volumes of oil.
There’s also the train of thought that “It’s only a small gearbox, so we just change the oil each year” thereby negating the need to carry out Oil analysis. We’ll be looking at Why this isn’t always the best thing in the next section
So, any machine containing rotating components which are lubricated with Oil or grease and which have the ability to physically access this lubricant, can be successfully sampled on a routine basis. Sealed for Life units being the usual exception.
Oil samples generally only require 60ml to be collected for analysis, there are some exceptions.
Why do you need oil analysis?
The arguments for not carrying out regular sampling and Oil Analysis usually contain reference to the “High Cost” whereas in fact the comprehensive test suites for most types of fluids can be obtained for less than £20.
Even a one-off analysis will provide a snapshot of what is occurring within the unit from which the sample has been taken. Identifying the chemical composition of the lubricant along with the levels of wear metals and the amount of contamination present in the sample is great; but to see and trend changes in these attributes regular samples must be collected.
Why sample the small volume unit mentioned earlier when it’s a cheap option to just keep changing the oil on a calendar or running time basis? The answer is simple, if you just dispose of the used lubricant, then the chance to determine the levels of wear to the bearings, gears, housings, or other internal components which may have occurred since the last change will be lost forever. Thus, when a failure occurs on a machine which has always been maintained that way, it will come as a surprise to the company; because they will feel that they have carried out all the necessary maintenance actions needed to keep it running. Whereas in fact the available wear history that could have been determined has simply been discarded.
The costs involved in an unplanned production outage far outweigh the small cost of that one additional sample which could have identified the progression of a fault from an early stage which if trended would have shown increasing levels of wear metals that could have been used to identify the likely source/type of the problem component and allowing for timely intervention to be planned.
What is Turbine Oil Analysis?
For an asset as valuable as a Gas or Steam Turbine, you’ll be thinking that all regular maintenance activities are carried out on time and correctly; but whilst vibration levels along with temperatures and pressures are monitored routinely to look for any signs of performance degradation or untoward changes that could affect the continued operation, wouldn’t it be beneficial to know just how well the Lubrication system is performing? In this article, I will be explaining all you need to know about what Turbine Oil Analysis is.
Why Should You Undertake Turbine Oil Analysis?
Changing the oil in your turbine is expensive, monitoring the performance and additive levels are not. This data will give you a trend that allows you to schedule and budget for the costly oil change.
What parameters for the lubrication system are checked, other than ensuring the reservoir content is sufficient and oil pressure and temperature are within the expected limits? The presence of Chip detectors and filter DPI gauges provide an indication that there is a build-up of debris.
Would it be beneficial to know how the oil is performing in relation to the design standard? You could say that temperature and pressure values are sufficient to satisfy this requirement. However, those aspects do not show the chemical changes which are occurring in the circulation system content.
How much longer will your oil continue to provide the key functions of cooling, lubricating, and protecting. The expense involved in changing out the oil for these assets is not something that can be taken lightly, so carrying out a premature change to be on the ‘safe side’ brings that forward, but at significant cost. Also if you have no analysis how do you know if your change is premature or too late?
When Should You Complete Turbine Oil Analysis?
At regular intervals, samples should be sent away for analysis to assess several key aspects of the lubricant’s chemistry, examine the physical properties of the oil and identify any contamination. Monthly analysis should be carried out to keep trends relevant for the basic analysis suites. The full turbine suite to include the oxidative ability and remaining antioxidants should be carried out at a minimum every 6 months.
What Tests Are Completed As Part of Turbine Oil Analysis?
A full turbine oil analysis suite should consist of the following:
|Rotating Pressure Vessel Oxidation Test (RPVOT)||D2272-14a||This test evaluates the oxidative stability of the lubricant. The lubricants ability to resist oxidation and degradation under high temperatures, water contamination, oxygen, pressure, and a copper coil catalyst.|
|Remaining Useful Life Evaluation Routine (Ruler)||D6971-09 + D6810||This test monitors the % of remaining amine and phenol additives (which are primary antioxidants) compared to the new reference oil. These additives basically neutralise by-products of oxidation to stop the cycle of oxidation.|
|MPC Varnish Potential||D7843-18||This test filters out the insoluble matter of turbine oil. The insoluble matter is then heated up and the colour is recorded using a spectrophotometer. This value is proportional to the lubricants potential to form harmful varnish and sludges.|
|Visual Inspection||n/a||The visual appearance of the oil and any particulates is noted to support the analytical results of the other tests.|
|Ferrous Wear Content (FW)||D8184||A total measure of ferrous particles in the sample irrelevant of size.|
|Elemental analysis||D7303-12||Measures several elements to identify wear issues, contaminant levels and chemical composition of the lubricant|
|Viscosity at 40°C||D7279-14A||A quality check to ensure the lubricant is still in the specification and therefore retaining its ability to lubricate.|
|ISO Particle count||ISO4406||The particulates within the sample are analysed and counted to identify any particulate contamination issues.|
|Total Acid Number (TAN)||D66411A + D974-14E02||The total acid number allows the acidity of the lubricant to be analysed which gives us a trend and allows us to predict when oxidation is occurring.|
|PPM Water Analysis||D6304-07||The CKF is used to determine the water content of the lubricant. This is compared to the reference oil to account for known additive interferences.|
|Fourier Transform Infrared (FTIR)||E2412||This allows the used lubricant result to be overlayed with the spectrum from the reference oil which will show changes to the chemical composition of the lubricant over time. Indicates oxidation, nitration, sulphation and contaminants.|
|Bacteria||D6974-09R13E2||Allows us to determine if any microbial growth is likely to occur in the oil tank due to steam, condensate or water contamination.|
What Does A Turbine Oil Analysis Report Look Like?
A typical turbine oil analysis report is shown below. You can download our example turbine oil analysis report by clicking here.
Adhesion is the result of two parts that drag across one another without adequate lubrication-film separation. This is also called Boundary Wear or Boundary Lubrication. The particles can be scuffed with striations from the dragging. The particles may show signs of melting due to the localised over-heating. Spherical particles are common when compete melting occurs.
Microdelamination is surface damage caused by steady state sliding and metal to metal contact at the microscopic asperity level. Damage occurs due to the plastic deformation at, or just below, the surface. The stress creates voids in the sub-surface belby layer initiating cracks. Cyclic motion causes the cracks to propagate resulting in particles which flake off.
Asperity Deformation is caused by micro microscopic asperity contact that results in the asperities on the softer material plastically deforming, or smearing in the direction of movement. Repeated contact eventually leads to removal of the asperities at the weakest point.
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Abrasive wear particles are most commonly the result of dust or dirt in the oil. The dirt particles become wedged between two moving parts, embed in the softer surface, and cut into the harder one. The wear debris from this process appears to be miniature shavings from a machining operation.
Abrasive wear particles can be several hundred microns long. Hard metals tend to form smaller abrasive particles that may have a needle-like appearance.
The primary corrective action for abrasion is to filter the oil to remove the contaminants. It is also important to minimise the ingress of contaminants, especially dust.
Fatigue wear is the result of repeated cyclic loading of surfaces with compression and shear or compression and tension. This is most common in industrial bearings and gears.
The repeated loading of the same point on a gear or bearing causes micro-cracks to form and become interconnected. When the cracks intersect surfaces, spall occurs and flakes or chunks are released into the oil. These particles are commonly 10 to 30 microns at first and later grow to be 100 microns or more. Fatigue is often from one of the following root causes:
- Improper assembly
- Other conditions which concentrate loading in a non-uniform distribution.
Corrosion and Lubrication Degradation
Corrosive problems are caused by water or other corrosive process media in oil, such as natural gas or sulphur.
Corrosion is especially a problem in refineries and crude oil processing facilities. Corrosive wear in industrial machinery is normally caused by contamination of the oil by water or other corrosive fluid.
Corrosive wear in engines can also be caused by degraded oil. Oxidation is a common way that oil gets degraded. Oxidation is caused when hydrocarbon oil molecules chemically react with oxygen from combustion gases, the atmosphere or moisture.
Long term high temperatures cause rapid oxidation. Measure the change in the dielectric constant, Total Acid Number or Fourier Transform Infra-red (FT-IR) to give an indication of when to change the oil.
Also, look at the colour of the oil. If it is degraded, then it will be very dark in colour (brown to black). Keep in mind that it may be dark and still be perfectly good, but if it is bad due to oxidation or other chemical deterioration it should also be very dark. Dielectric increase of 0.1 usually means its time to change the oil.
No industrial oil analysis is complete without a comprehensive Wear Debris Analysis. Wear Debris Analysis (WDA) is a non-intrusive way to see inside complex machinery without taking it apart. Accurate identification of wear debris fragments can tell you which machine elements are damaged, and the nature of the problem which generated the debris.
Most (80%) of abnormal machine wear comes from one of four mechanisms:
Wear Debris Analysis tells you both the mechanisms and the severity. Armed with this knowledge, you can go after the corresponding route causes such as dust contamination, vibration faults, lubricant starvation or water contamination.
Cleaning up your oil storage and using clean and correctly labelled storage containers is the first step in gaining control of your lubrication programme.
Care should be taken when handling lubricants. Incoming and used oils should be checked for contamination and to ensure that the correct oil is being used. Many problems may occur with wrong, mixed or contaminated oils throughout the plant.
At the least:
- Label all your oils correctly with dielectric and viscosity.
- Clean up.
- Correctly label containers and equipment.
- Accurately label sample bottles.
- Store lubricants in a clean, dry location and use desiccating breathers.
- Transfer lubricants using dedicated, tagged totes.
Contamination can best be controlled by learning what the contaminant is and identifying where it has come from. Contaminants may have many sources, including moisture, acquired when sampling oil. Dirty or hazardous environments such as coal handling or chemical refineries have their own problems, as do cement plants and wet environments.
Proper storage and handling of lubricants is a necessary first step, but this is often not enough. Exclusion technologies such as ensuring proper sealing of lubrication reservoirs on machinery is often the right solution. Filtration systems such as exclusion breather systems can greatly reduce contamination of particulates as well as moisture. Regardless of what solution is successful for your application, regular monitoring is necessary to maintain the integrity of your lubrication programme.
Oil analysis, or oil analysis Tribology, is a non-intrusive means of determining whether the oil system is clean and dry, if the oil is fit for use, and if wear is occurring inside the machine.
A machine’s operating life is most often determined by the oil that lubricates its load-bearing surfaces. Good lubrication normally provides long life, even under harsh operating conditions, and poor lubrication results in short life, even under mild operating conditions. Industrial machines are generally supposed to have 40,000 hours (about 5 years) mean time between failure (MTBF). This can only happen if you have “good lubrication”. If you have “poor lubrication” or “no lubrication” you get a far shorter operating life.
There are 5 factors in maintaining good lubrication:
- Clean oil
- Dry oil
- Oil with the right properties
- Contamination Control
- Wear debris monitoring
Particle counting is used to monitor the cleanliness level of the machinery. The cleaner the system, the longer it lasts.
Wear debris analysis is used to identify the root cause of abnormal conditions. This analysis of large particles provides the essential difference between conventional oil analysis and industrial oil analysis.
Viscosity is one of the most important properties of an oil. Without the correct viscosity a machine will not have the correct lubrication, resulting in severe damage. Viscosity is measured at 40°C and 100°C as it can differ significantly depending on the operating temperature.
Spectometric analysis is used to measure wear metals (partical size typically less than 5 microns), contaminants such as silica (dust) and additives levels (adding wrong lubricant, addaiive depletion)