Products Cate

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Nationallube Australia Agriculture Lubricants Products Range. Code Product…

Read More

Lubricant Storage

Lubricant Storage, Stability, and Estimated Shelf Life

Lubricating oils and greases deteriorate with time like most of the material. Proper storage practice is to ensure sufficient stock turnover of the lubricants and their usage before any significant performance loss has occurred.


Conditions Affecting all Lubricants

The storage environment greatly affects the shelf life of lubricants and greases. Conditions, which needs to be monitored, are: Temperature: Heat (greater than 45°C) and cold (less than 20°C) can affect lubricant stability. Heat increases the rate of oil oxidation, which may lead to formation of deposits and viscosity increase. Cold can result in wax and sediment formation. In addition, alternating exposure to heat and cold may result in air being drawn into drums, which may result in moisture contamination. A temperature range of 20°C to 45°C is acceptable for storage of most lubricating oils and greases.

Light: light may change the color and appearance of lubricants. Lubricants should be as far as possible kept in their original metal or plastic containers.

Water: water may react with some lubricant additives, sometimes forming insoluble matter. Water can also cause microbial growth at the oil/water interface. Lubricants should always be stored in a dry location, preferably inside.

Airborne Contamination: drums and pails should not be stored in areas where there is a high level of airborne particles. This is especially important when a partially used container is stored. oxygen and carbon dioxide can react with lubricants and affect their viscosity and consistency. Keeping lubricant containers sealed until the product is needed is the best protection.

Condition Affecting Greases

Grease properties can change during storage depending on the type of thickener, its concentration, the base fluids, and the additives used. One condition that commonly affects greases is:

Oil Separation: oil will naturally separate from most greases. Temperatures in excess of 45°C can accelerate oil separation. If grease is removed from a drum or pail, the surface of the remaining grease should be smoothed evenly to prevent oil separation into the cavity.

Recommended Storage Conditions and Practices for Lubricating Oils and Greases

  1. Store lubricating oils and greases in a cool dry indoor area where airborne particles are at a minimum. Indoor storage also prevents deterioration of label and container from weather. The ideal storage temperature range is from 0°C to 25°.
  2. When necessary, bring grease to satisfactory dispensing temperature just prior to use.
  3. If drums must be stored outside, use plastic covers or tip oil drums to direct water and contamination away from the bungs. Always store greases upright to prevent oil separation. Keep containers tightly covered or closed to avoid contamination
  4. Use clean tools and equipment when pumping or handling lubricants and greases
  5. Rotate the inventory. Check the container manufacturing date and use the oldest container first.
  6. Wipe off the tops and edges of containers before opening to avoid contamination.

Products Exceeding the Estimated Shelf Life

A product in an unopened container, which is beyond the estimated shelf life, may still be suitable for service. The product should be tested and evaluated against the original product specifications. If in doubt call your local Nationallube dealer to ascertain the further course of action .


OILS, AND GREASES SHELF LIFE

Product Years
Base OilsLubricating Oils (mineral / synthetic) 5+
Greases (mineral / synthetic) 5
Cutting Oils 5
Exceptions:  
Rust Preventives 2
Open Gear Lubricants 2

 

Viscosity Classifications
The first and most important task of a lubricating oil is to keep moving metal parts separated from each other thus avoiding metal-to-metal contact which leads to destructive wear. Even finely machined metal surfaces still have a certain roughness. Contact of these minute metal projections should be minimized. Some contact always occurs and results in normal wear of the metal surfaces. However, if contact is not minimized, the touching metal parts generate a lot of heat. The heat results in local welding and transfer of metal. This results in scuffing or seizing of the equipment. This is called adhesive wear. The oil property that governs the thickness of the separating oil film is the viscosity.

Definition:

Viscosity
The commonly used kinematic viscosity is defined as: a measure of the restrictive flow of a fluid under gravitational force. The "cgs" unit of kinematic viscosity is one centimeter squared per second, called one Stokes (symbol St). The SI unit for kinematic viscosity is one meter squared per second and is equivalent to 10.000 St. Usually the centistokes (cSt) is used. (1 cSt=10-2St=1 mm2/s).

Viscosity Index (VI)

The viscosity of lubricating oil changes with temperature. The rate of change depends on the composition of the oil. Naphthenic base oils change more than paraffinic base oils. Certain synthetic lubricants change much less than paraffinic oils. To access this property of a lubricating oil the American Society for Testing and Materials (ASTM) created a method to provide a number called the Viscosity Index (VI) which correlates the amount of viscosity change for a given oil compared to two reference oils having the highest and lowest viscosity indices at the time when the VI scale was first introduced (1929). A standard paraffinic oil was given a VI of 100 and a standard naphthenic oil a VI of 0. Tables have been prepared which show the relationship between viscosities at 40 and 100°C. The method has been updated and revised several times to include VI values higher than 100.

The important thing to remember is: a low VI means a relatively large viscosity change with temperature and a high VI denotes a smaller change of viscosity with temperature. Hence, the VI of an oil is of importance in applications where an appreciable change in temperature of the lubricating oil could affect the start-up or operating characteristics of the equipment.

Viscosity Classification:

Engine Oils
As the selection of the proper viscosity grade is extremely important, various viscosity classification systems have been developed over the years. The viscosity classification for engine oils was developed by the Society for Automotive Engineers (SAE) in 1911. This classification system is, after many revisions and updates, still in place. The current SAE J300 Viscosity Classification is shown in Table 1.

The SAE grades 0W through 25W, where W stands for Winter, have a maximum viscosity specified at low temperatures (5 through 35°C), to ensure easy starting under low temperature conditions, and a minimum viscosity requirement at 100°C to ensure satisfactory lubrication at the final operating temperature. The SAE grades 20 through 60 only have limits set at 100°C as these grades are not intended for use under low temperature conditions. For marine applications, monograde oils of SAE 30 or SAE 40 are used because of the steady operating conditions in a ship's engine room.

On the other hand, automotive oils are normally formulated with Viscosity Index Improvers (VI Improvers) to provide multigrade performance.

VI Improvers are very large molecules, which are chemically made by linking together smaller molecules in a process called polymerization. The resulting products, called polymers, may have molecular weights 1000 times or more greater than the base stock molecules.

The use of these special polymers makes it possible to meet both the low temperature viscosity requirements of the W grades as well as the high temperature requirements of the non-W grades.

If we take a 15W-40 multigrade engine oil the typical viscosities are:
 
Viscosity at 15°C, cP* 3000
Viscosity at 40°C, mm2/s (cSt) 105
Viscosity at 100°C, mm2/s (cSt) 14
Viscosity Index 135
From this example it can be seen that the high VI gives a relatively small change in viscosity with temperature, and as a result of the high VI the multigrade oil meets both the 15W grade low temperature viscosity requirements as well as the 40 grade high temperature viscosity requirements.

Viscosity Classification: Industrial Oils

Many different viscosity classification systems have been used in the past in different parts of the world. It has been very difficult to reach agreement on the number of different grades to be included, the viscosity limits for these grades, and the temperature at which the viscosity should be specified. It is only since 1972 that a worldwide viscosity classification system for industrial lubricants came into place. The current ISO 3448 viscosity classification system, which is also adopted by the ASTM, is shown in Table 2.

The classification is based on a series of viscosity grades, each being approximately 50% more viscous than its preceding grade while the viscosity deviation within a grade is plus or minus 10% of the nominal viscosity of that grade.

Used Oil Viscosities

Used lubricating oils may show an increase of the viscosity due to oxidation/ nitration or contamination like soot loading of a diesel engine oil.

Viscosity results of used lubricating oil samples are compared with the Original Equipment Manufacturer's requirements whenever possible. If this is not feasible, the generally accepted limit as regards viscosity change is ±25% of the fresh oil value.
 
TABLE 1: SAE VISCOSITY GRADES FOR ENGINE OILS
SAE Viscosity Grade Viscosity (cP)* at Temperature (°C), Max Viscosity mm2/s (cSt) at 100°C
Cranking Pump Ability Min Max
0W 3250 at 30 30,000 at 35 3.8 -
5W 3500 at 25 30,000 at 30 3.8 -
10W 3500 at 20 30,000 at 25 4.1 -
15W 3500 at 15 30,000 at 20 5.6 -
20W 4500 at 10 30,000 at 15 5.6 -
25W 6000 at 5 30,000 at 10 9.3 -
20 - - 5.6 < 9.3
30 - - 9.3 < 12.5
40 - - 12.5 < 16.3
50 - - 16.3 < 21.9
60 - - 21.9 < 26.1
*1cP = 1centipoise = 1mPa.s. This dynamic viscosity can be converted as follows: Dynamic Viscosity = Density x Kinematic Viscosity
TABLE 2: INDUSTRIAL LUBRICANT VISCOSITY CLASSIFICATION
Viscosity System Grade ISO Standard 3448 ASTM D-2422 Mid-Point Viscosity, mm2/s (cSt), at 40°C Kinematic Viscosity Limits, mm2/s (cSt), at 40°C
Max. Min.
ISO VG 2 2.2 1.98 2.42
ISO VG 3 3.2 2.88 3.52
ISO VG 5 4.6 4.14 5.06
ISO VG 7 6.8 6.12 7.48
ISO VG 10 10 9.0 11.0
ISO VG 15 15 13.5 16.5
ISO VG 22 22 19.8 24.2
ISO VG 32 32 28.8 35.2
ISO VG 46 46 41.4 50.6
ISO VG 68 68 61.2 74.8
ISO VG 100 100 90.0 110
ISO VG 150 150 135 165
ISO VG 220 220 198 242
ISO VG 320 320 288 352
ISO VG 460 460 414 506
ISO VG 680 680 612 748
ISO VG 1000 1000 900 1100
ISO VG 1500 1500 1300 1650
 

What About Water in the lubricating oils?

The water content of used lubricating oils can be measured in a number of ways. A simple "go/no go" test for water is the so-called "crackle test". A few drops of oil are placed on an electric hot plate. If the oil starts to bubble and spatter, water is present. Even as little as 0.1% of water in the oil can be detected this way. However, this test does not give any indication of the amount of water in the oil. A rapid and accurate test method for the quantitative measurement of the water content in oil is based on the chemical reaction of water with calcium hydride. The reaction that takes place releases a small amount of hydrogen gas, which is captured in a container. The pressure increase in the container is measured and can be converted to the amount of water present in the oil sample. Many water determination test kits for shipboard use are based on this principle.

Test method ASTM D-95 for water in lubricating oil is based on a totally different principle. In this test equal volumes of oil sample and diluent solvent are subjected to a distillation test. The water and solvent vapors are condensed in a cooler and the condensed liquid is collected in a trap. The water separates from the

solvent at the bottom of the trap due to its higher density. At the end of the test the total volume of water collected in the trap is recorded and converted to the water content in the oil.

Another well known test method which enables the actual water content in the oil to be calculated to determine very low quantities of water is ASTM D-1744, or the "Karl Fischer" method. With this procedure water levels as low as 50 mg/kg (ppm) can be detected. The method is based on a chemical reaction of the water with the Karl Fischer reagent.

Finally, there are a number of laboratory test methods, which are based on the use of a centrifuge to separate the water from oil samples.


Origin of Water Contamination

Water contamination of fresh and used lubricating oils may originate from various sources. Due to differences between day and night temperatures lube oil storage tanks are more or less continuously breathing. During the night hours, when the temperatures are lower than in the daytime, ambient air containing a certain amount of water vapor will be drawn into the tank vapor space. Some of the water vapor will condense on the tank walls. As a result of this process over time a significant amount of water may collect at the bottom of a storage tank. This phenomena can hardly be avoided. The proper action to be taken is a regular check for the presence of water. If a significant amount of water is detected, the water should be drained.

Ventilation openings in storage tanks are another source of water. These openings should be shielded to avoid ingress of rain or seawater.

In some equipment free water and/or water vapor is unavoidably generated during operation. Air compressors are very prone to water contamination because during compression the water vapor present in the air will condense under certain unfavorable operating conditions. Regular removal of condensed water is of utmost importance to protect the equipment.

Diesel engines used for propulsion as well as for power generation produce water vapor during combustion of the fuel. Under adverse operating conditions this water vapor and the moisture from humid combustion air may condense in the crankcase and mix with the oil. Large quantities of water sometimes enter the crankcase due to leaking cooling systems.

Another well-known problem area is leakage of stern tube seals.

Why all this Attention to Water?

Water is the most common contaminant present in used lube oil samples from all kinds of equipment. Excessive water contamination over a prolonged period of time will eventually lead to equipment failure since the following problems may occur:

  • Sludge formation in the oil, followed by possible oil line plugging.
  • Reactions of the additives present in the lubricants with water will impair the effectiveness of these additives; in extreme cases this may result in precipitation of the additives.
  • Rusting and corrosion, leading to high wear and bearing failures.
  • Impaired lubrication film from water or steam pockets in heavily loaded bearings.
  • Formation of emulsions which will impede oil purification and lubrication.
  • Bacterial growth on the water/oil interface, leading to corrosion and undesired changes in the lubricating oil characteristics.

In-service Warning Limits

The maximum tolerated level of water contamination differs slightly for the various types of equipment being lubricated, various kinds of lubricating oils, and various operating conditions. The table below shows a general summary of the warning limits for water contamination of the lubricating oil in service based on experience and manufacturer's requirements. Finally, the best recommendation we can give is to be alert, stop the ingress of water as soon as possible and keep your oils "dry".

 
 
Warning limits for water
Equipment Vol.%
Diesel Engines 0.20.5
Turbo Chargers 0.2
Steam Turbines 0.2
Gear Boxes 0.2
Turbo Generators 0.2
Hydraulic Systems 0.2
Air Compressors 0.2
Refrigeration Compressors 0.1