Can I mix different viscosities of oils to get the viscosity that I want?
It can be done but this is not an ideal situation.
There are times when the only available viscosity is an ISO 46 (on a rig) but the equipment requires an ISO 68 and the new stock will not be delivered in time to avoid shutdown. Can the ISO 46 be used instead?
An ISO 46 oil is lighter in viscosity than an ISO 68 however, for most oils, there is a chart that depicts the viscosity of the oil at operating temperature. In these cases, one can consult this chart and determine if the viscosity at operating temperature will still fall within operating limits.
If we mix an ISO 46 with an ISO 68 oil we cannot be certain of where the new viscosity will fall especially if we do not know the ratios that are being used. There is a viscosity calculator that can help guide this decision available at: https://www.widman.biz/English/Calculators/Mixtures.html
This can be used as a guide and the actual values of the oil should be verified via oil analysis.
While this situation is not ideal, we need to remember that compatibility is also key.
As such, we should stick with the same line of lubricants that we being used. Typically, lubricant suppliers have the same formulation but change the viscosities for lubricants of the same line.
Always follow what the OEM recommends! A quick google search can help you find the required lubricant if you don’t have the owner’s manual.
Most modern vehicles use lighter weight oils compared to older vehicles. Let’s think about cars back in 1950. They were larger, with big engines. With a big engine, it would mean that the lines carrying the oil would be larger. Thus, a heavier oil (50 weight) would be the most appropriate.
Now, fast forward to cars today. The engines are smaller, (albeit with a lot more horsepower as well!). If the size of the engine has changed, then the size of the lines carrying the lubricant will change as well. These lines will get smaller. If the lines are smaller, then the liquid that has to flow through them, should be lighter (thinner).
We can use an analogy of a straw trying to pull up molasses.
With a large straw, we could pull up the molasses faster than with a thinner straw. This is similar to the older cars, they would have thicker “straws” (lines) that would have allowed them to adequately pump the lubricant.
In the newer cars, the straw has gotten thinner, so it can’t pull up the molasses anymore. If we tried to pull up water instead, it would definitely flow faster than the molasses and not have as much strain on the person pulling up the water (pump in the engine). Hence, lighter oils are used in modern cars.
Most recommendations can be found by contacting the OEM or even doing a bit of Google searching with the year of manufacture for the car and of course the model.
One of the major types of oil degradation is Oxidation. But what is it exactly, as applied to a lubricant?
Oxidation is the addition of oxygen to the base oil of the lubricant to form either of the following:
Wow… too many chemical names right?! These help to pinpoint the conditions responsible and then we can address them accordingly. Each of these by products are produced by different types of reactions or in some cases different stages of the oxidation process. It is key to note the type of by product as it gives us a clue to the root of the issue through which oxidation occurs.
For instance, the presence of Carboxylic acids can result in the formation of Primary Amides which can lead to heavy deposits. Early detection of the Carboxylic acids can help us prevent this. Once we determine the source of oxidation to produce the carboxylic acids, we can in turn remove this from the system.
Oxidation does not happen in an instant. Usually, it follows a series of events which eventually lead to oxidation. Like any process in life, there are different stages for Oxidation:
Initiation – Production of the free radical via the lubricant and catalyst.
Propagation – Production of more free radicals via additional reactions
Termination – Continuation of oxidation process after the antioxidants have been depleted or the antioxidant stops the oxidation process.
Results of Oxidation
Why is Oxidation bad for the lubricant? What can it ultimately result in?
Well, oxidation can result in the formation or lead up to the following:
Loss of antifoaming properties
Base oil breakdown
Increase in viscosity
None of these are good for the lubricant!!!!!!!!! If you see any of these signs be sure to test for oxidation and identify the root cause for the introduction of oxygen in your system.
Now that we know more about oxidation… what tests can be performed to prevent it?
There are 6 main tests that can be performed:
RPVOT (Rotating Pressure Vessel Oxidation Test)
RULER (Remaining Useful Life Evaluation Routine)
MPC (Membrane Patch Calorimetry)
FTIR (Fourier Transform Infrared)
Colour (ASTM D1500)
Acid Number (ASTM D974)
One must be careful in selecting which test to apply, this is heavily dependent on the type of lubricant and its application.
For instance, if we perform the RULER test and the antioxidant levels have depleted significantly, we can suspect that oxidation is occurring or has stopped. Charting the rate of antioxidant depletion, can determine the rate of oxidation. This can assist us to forecast the time remaining before antioxidants have been depleted and can no longer protect the base oil.
Quite often, when lubrication failures occur, the first recommended action is to change the lubricant. However, when the lubricant is changed, the real root cause of the lubricant failure has not been solved. As such, the cause of lubrication failure will continue to be present and may escalate further to develop other problems.
Essentially, this can cause catastrophic future failures simply because the root cause was not identified, addressed and eradicated. Moreover, the seemingly “quick fix” of changing the lubricant, is usually seen as the most “cost effective” option. On the contrary, this usually becomes the most expensive option as the lubricant is changed out whenever the issue arises which results in a larger stock of lubricant, loss in man hours and eventually, a larger failure which can cost the company at least a month or two of lost production.
In this article, we investigate lubricant failures in Ammonia plants and their possible causes. Some Ammonia plants have a developed a reputation for having their product come into contact with the lubricant and then having lubrication failures occur. As such, most Ammonia plant personnel accept that the process materials can come into contact with the lubricant and usually change out their lubricants when such issues occur. However, there are instances, where the ammonia is not the issue and plant personnel needed to perform a proper root cause analysis to determine the root cause and eradicate it. Here are a couple of examples of such instances.
Livingstone (1) defies the Lubrication Engineers Handbook in their description of ammonia as an inert and hydrocarbon gas that has no chemical effect on the oil, stating that this is incorrect. Instead, Livingstone (1) lists the number of ways that Ammonia can react with a lubricant under particular reactions such as;
ammonia being a base that can act as a nucleophile which can interact with any acidic components of the oil (such as rust/corrosion inhibitors)
reaction of ammonia with carboxylic acids (oil degradation products) to produce amides which cause reliability issues
transesterification of any ester containing compound to create alcohol and acids and the reaction of ammonia with oxygen to form NOx which is a free radical initiator that accelerates fluid degradation.
As such, one can firmly establish that ammonia influences the lubricant and can lead to lubrication failures should that be the cause of the lubricant failure.
The Use of Root Cause Analysis
Van Rensselar (2) quotes Zhou as saying the best method for the resolving varnish is to perform a root cause analysis. Wooton and Livingstone (3) also advocate for the use of root cause analysis to solve the issue of varnish. They go on to explain that the characterization of the deposit aids in determining the root cause of the lubricant degradation. As such, Wooton and Livingstone (3) have developed a chart to assist in deposit characterization as shown below.
Wooton and Livingstone (3) discussed that with the above figure, once the deposit can be characterized then the type of lubricant degradation can be more accurately identified. As such, the root cause for the lubricant degradation can now be firmly established thereby allowing solutions to be engineering to control and reduce / eliminate lubricant degradation in the future.
A case study from Wooton and Livingstone (3) was done with an Ammonia Compressor in Romania which experienced severe lubricant degradation. In this case study, they found that when the in-service lubricant was subjected to two standard tests namely MPC and RULER, both tests produced results within acceptable ranges. As such, there was no indication from these tests that the lubricant had undergone such drastic degradation as evidenced by substantial deposits within the compressor. Thus, it was determined that the deposits should be analysed as part of the root cause analysis.
For the deposits from the Ammonia compressor, Wooton and Livingstone (3) performed FTIR spectroscopy to discover that its composition consisted of mainly primary amides, carboxylic acids and ammonium salts. It was concluded that the carboxylic acids formed from the oxidation of fluid while in the presence of water.
In turn, the carboxylic acids reacted with the ammonia to produce the primary amides. These amides consisted of ammonium salts and phosphate. As such, the onset of carboxylic acids within the system eventually leads to the lubricant degradation. Thus, an FTIR analysisfor carboxylic acids was now introduced to this Ammonia plant as well as MPC testing to monitor the in-service lubricant.
Additionally, chemical filtration technology was implemented to remove carboxylic acids within the lubricant. These two measures allowed for the plant to be adequately prepared for lubricant degradation and avoid failures of this type in the future.
Another case study was done in Qatar with an ammonia refrigeration compressor which was experiencing heavy deposits due to lubrication degradation. For this Ammonia plant, high bearing temperatures and deposits were found on the bearing.
Upon investigation, it was realized that the lubricant had been contaminated externally and there was restricted oil flow to the bearings. After a FTIR was performed it was deduced that that the deposits were organic in nature and there were several foreign elements including high levels of carbon and primary amides.
From further root cause analysis, it was determined that the high temperatures observed were due to the lubricant starvation. Due to these high temperatures, oxidation initiated and with the high levels of contamination (mainly from ammonia within the process) this lead to degradation of the lubricant in the form of heavy deposits.
The bearing oil flow was increased and reduction in external contaminants were implemented. Oil analysis tests of Viscosity, Acid Number, Membrane Patch Calorimetry and Rotating Pressure Vessel Oxidation tests were also regularized in the preventive maintenance program. Thus, for this failure, some operational changes had to be made in addition to increased frequencies of testing. With these measures in place, there would be a reduced likelihood of future failures.
From the case studies mentioned, it can be concluded that ammonia systems have a higher possibility of undergoing lubricant degradation due to the contamination of the lubricant by ammonia gas / liquid due to its properties. However, it must also be noted that the ingression of ammonia into the lubrication system is not the only cause for lubrication failure.
Therefore, it is imperative that a proper root cause analysis be carried out to determine the varying causes for lubrication failure before the ingression of ammonia accepts full responsibility for any such failure.
Livingstone, Greg (Chief Innovation Officer, Fluitech International, United States America). 2016. E-mail message to author, March, 08.
Van Rensselar, Jeanna. 2016. “The unvarnished truth about varnish”. Tribology & Lubrication Technology, November 11.
Wooton, Dave and Greg Livingstone. 2013. “Lubricant Deposit Characterization.” Paper presented at OilDoc Conference and Exhibition Lubricants Maintenance Tribology, OilDoc Academy, Brannenburg, Rosenheim, Germany, United Kingdom, January 22-24, 2013.