In our recent post on oil analysis, we discussed how viscosity is considered one of the most important properties of a lubricant and how subtle changes in lubricant thickness can signal substantial maintenance issues.
This week, we’ll take a closer look at how an effective used oil analysis program monitors viscosity and the potential trouble signs to be aware of when analyzing results.
Kinematic viscosity testing is traditionally conducted by measuring the time needed for a fixed volume of lubricant to flow under gravity through a viscometer when heated at a closely controlled temperature – typically 40°C (104°F) or 100°C (212°F).
At these temperatures, a lubricant’s speed of descent is measured in centistokes (cSt) in line with international standards. The lower the viscosity, the lower the measurement in cSt. For example, water has a viscosity of one cSt, compared to Mobil SHC 634, which has a typical viscosity of 460 cSt. These viscosity measurements are then used to classify fresh oils into different viscosity grades, per ISO standards. For example, an ISO VG 32 oil has a typical fresh oil viscosity around 32 cSt, while an ISO VG 680 fluid has a typical fresh oil viscosity around 680 cSt.
As extreme operating temperatures can affect viscosity to a level that lubricants are no longer able to provide adequate equipment projection, monitoring viscosity changes through a used oil analysis program can help maintenance personnel minimize equipment downtime, reduce costs and enhance safety.
Change in viscosity from typical fresh oil levels may indicate that corrective action should be taken. The amount of change that is acceptable prior to corrective action depends on the product formulation, the application, history of the equipment, among other factors. Many lubricant manufacturers set limits within their used oil analysis programs regarding the amount of viscosity change that should trigger corrective action.
A decrease in viscosity may indicate that oil films are not sufficient to protect equipment from wear damage. Reduced viscosity can be caused by a number of different factors, such as:
An increase in viscosity may result in reduced performance from the oil, for example poor cold start pumpability or poor demulsibility. Increased viscosity can be caused by a number of factors, including:
Clearly, viscosity is one of the most important properties of a lubricant, but it’s just one area that is monitored in a comprehensive oil analysis program. Next week we’ll continue our discussion on the other key areas of oil analysis by examining additive elements, wear metals and contaminants testing.
Some typos in this briefing guys !
John, I think we fixed them -- let me know if we missed any, and thanks! That's a pretty sharp eye you have there!
Can you explain more about Nitration ?
I’ve provided two tech topics for you to refer to in Downloads. I’ve included a bit of the information from these documents below. Nitration can be found in hydraulic systems and in natural gas powered engines.
From the hydraulics Tech Topic:
Nitration indicates a fluid is reacting with nitrogen oxide compounds and creates varnish that sticks primarily to valves. Field test shows that nitration increases when ambient air temperatures rise and or become higher, Additionally, mechanical conditions such as lower oil makeup, poor ring sealing, and poor ventilation also expedite nitration.
From a natural gas engine oil Tech Topic:
Nitration is an undesirable condition which indicates that the oil in natural-gas-fueled engines is becoming saturated with the soluble and/or insoluble nitrogen oxide compounds. The reaction of nitrogen with the base oil forms two kinds of nitrogen compounds: organic nitrates and nitro compounds. They are independent of the oxy-products that lead to oil oxidation, which is another form of oil degradation.
Good article where it speaks about the compression of the Oil Analysis with the following factors: Oxidation or nitration; Mixture with heavier grade Oil, soot load (on mobile Equipment); and the Oil Contamination
Good ìnormation for me