How to Avoid Particulate Contamination

Michelle Allis, Wearcheck Africa
Tags: lubricant storage and handling

It is widely accepted that oil contamination is one of the major causes of component failure. When practicing proactive maintenance, it therefore makes sense to give oil cleanliness a high priority. By maintaining a high level of oil cleanliness, effects such as machinery failure, resultant downtime and expensive repair costs can be kept to a minimum.

There are many factors to consider when cleaning up your act. The first and most important place to start is at the source: the new oil. Oil could be contaminated when it leaves the refinery, during transportation or during the transfer to the end-user's or vendor's tanks. But more often than not, it is the manner in which the oil is stored by the user that results in new oil contamination.

Oil Storage
Oil storage is an important factor to consider when implementing proactive maintenance, but it is usually at the bottom of the list of priorities or overlooked completely. Many times, the area and manner in which the oil is stored can introduce contamination. So how do you ensure that this does not happen? Let's take a closer look at proper oil storage conditions.

The most common oil container used by the oil industry is the 210-liter (55.5-gallon) drum. Filled with oil, it weighs approximately 220 kilograms (485 pounds). These drums should be handled carefully to prevent damage to the drums, causing them to puncture or burst. Containers should be moved immediately to a storage area and remain sealed until needed. Oil drums or containers should be stored indoors whenever possible.

To avoid contamination when storing oil outdoors:

  • Do not store the drums outside indefinitely, because drums can rust and contaminate oil.

  • Ensure bungs are tight and that drum seams do not deteriorate. This can occur because temperature changes lead to expansion and contraction of the metal, causing oil leaks or contamination.

  • Keep drums or containers as dry as possible and away from water. Do not allow water to accumulate on any part of the container. This water can be drawn into the container when changing temperatures cause pressure changes within the drum or container.

  • Store the drums under a roof, a lean-to or cover with a tarp.

  • Before removing bungs, dry and clean around the bung areas to prevent contamination with dirt and water - the two most common and destructive contaminants in any environment.

  • Lay the drums on their sides, on a specially constructed rack if possible. Make sure that the bungs are in the 3 o'clock and 9 o'clock positions. This generally ensures that the content of the drum is above the bung level. This minimizes water (and dirt) entry and stops the seal from drying out. If drums must be stored upright without any protection from the elements, tilt them slightly and make sure the tilt is parallel to the 3 o'clock/9 o'clock bung line. This prevents water from collecting around the bungs.

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When storing oil containers or drums indoors, remember the following tips:

  • The storage area should be a cool, dry area free from extreme temperatures.

  • Keep the storage area clean at all times, with a formal cleaning schedule in place.

  • Minimize the presence of any contaminants. Contaminants could result from manufacturing processes, the environment, etc.

Oils can also be stored in bulk storage tanks. It is often easier to maintain low particulate contamination levels when oils are stored in bulk tanks because they are normally closed to the atmosphere and the oil is dispensed via a pump or tap. Ensure the seals are intact and fitted with desiccant (recommended) breathers.

Oil Dispensing
Contamination due to dirty top-up containers or dispensing equipment is a common problem. As with most of the points raised with storage, hygiene and common sense are what count. Dispensing equipment should be kept clean to minimize contamination of the oil. Keep in mind these few points:

  • Make sure pumps and portable lines are kept clean and are stored in a clean environment.

  • Avoid topping up and filling in exposed areas.

  • If top-up containers must be used, make sure they are clean and not left open to the elements. Avoid mixing different oils in these containers.

  • Quick-coupling fillers will ensure that environmental contaminants do not enter lubrication systems.

  • A number of companies produce utility cans for topping-up purposes. These have lid and spout designs that keep contaminants out, and some have a pressurized dispenser.

  • Clean around filler caps before removing.

  • Make sure the tops of drums are clean and free from dirt and water before opening.

Once sufficient oil storage has been established, the next place for oil particulate contamination to occur is once the oil is in the machine or component. This can happen in many ways. Open vents provide an easy means for dirt to enter machines. Faulty breathers are a common source of particulate contamination. Oil leaks or damaged seals are also culprits. Remember, if oil is able to leak out of a system, contaminants are able to enter the system. Repair damaged seals or oil leaks as soon as possible.

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Internal Contamination
Some form of internal particulate contamination is inevitable and can denote a problem with the machine/component. Internal particulate contamination includes any particles that contaminate the oil once it has been placed in the closed lubricated system - for example, wear particles, seal material, etc. When external particulate contamination is under control, a high particle count provides an early warning for an abnormal wear situation developing.

Particles, especially catalytic metal particles like copper, iron and lead, increase the oxidation rate. These particles also strip the oil of its antiwear additives, extreme pressure additives, rust inhibitors and dispersants. Numerous small particles in stable suspension can cause the oil's viscosity to increase and may promote foaming.

These particles are abrasive. As with all particulate contaminants, once in the oil, they accelerate the wear rate dramatically because abrasive wear can cause a chain reaction in lubricated machinery. The typical chain reaction is:

  • Abrasive wear particles become work hardened.

  • Work hardened particles produce more particles.

  • New particles become work hardened.

  • Chain reaction occurs until the particles are removed by filtration or the machine fails.

It is, therefore, imperative to monitor oil cleanliness and keep particulate contamination to a minimum. This is accomplished by implementing a contamination control program in these easy steps:

Contamination Prevention
After ensuring oil is free from contamination, consider the times when servicing the machine becomes necessary. When component changes or work is performed on the machine, make sure that all new components are free from contamination and that further contamination does not enter the machine during servicing. Ensure that all seals and breathers remain intact to prevent contaminant entry.

Contamination Removal
Contamination removal is accomplished with filters and filtration systems or oil draining and discarding. Each application must be evaluated when deciding which option is more cost-effective. Using filters to achieve target cleanliness levels does not always require the best or most expensive filter. A cheaper filter used correctly may produce the desired results at a lower cost. The effectiveness of a filter or filtration system can be tested by taking representative oil samples from before and after the filter.

Monitoring Cleanliness Levels
For effective monitoring of the oil, check for cleanliness levels in the machine as well as at several other points, such as new oil sources, bulk tanks or stored lubricants, or oil in service in equipment.

To monitor the level of contamination, test the oil and obtain a particle count. Different instruments using different methods are available to test particle count. Wearcheck uses the most common type of automatic particle counter, which operates on a light blockage principle. In this particle count test, the total number of particles, irrespective of origin, are counted in a number of sizes, ranging from greater than 5 to 100 microns.

The results are expressed as the total number of particles per milliliter of oil in the various specified size ranges. A cleanliness rating is also reported. The cleanliness rating is expressed as a two-number code X/Y, where X represents the total number of particles per ml greater than 5 microns and Y represents the total number of particles per ml greater than 15 microns.

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Target Cleanliness Levels
For warranty purposes, certain manufacturers have established maximum cleanliness ratings for their equipment. It is, therefore, difficult to know what the optimum cleanliness level is for your machines. Each machinery class has an appropriate oil cleanliness level for that application. In general, machines with tight clearances benefit greatly from clean oil.

It takes time to monitor results and choose an exact level if you haven't been given one by the manufacturer. Be realistic and consider what is cost-effective when setting target cleanliness levels. It makes no sense to expect such high cleanliness levels that you spend more money discarding or filtering your oil than it would cost to replace the machine in the event of a failure.

Sampling technique is of utmost importance when monitoring cleanliness levels. Sometimes an oil may have a high particle count result, but the actual oil in the machine is perfectly clean. This could be the result of two scenarios:

First Scenario
Ensure that the oil sample taken is representative of the oil in the machine. The oil should be well mixed when the sample is taken and no external contamination should be introduced during sampling. This external contamination could result from factors such as:

  • A dusty environment

  • A manufacturing process that produces particulate contamination

  • The oil not being well mixed and sediment from the tank bottom draining into the oil sample bottle

  • A dirty sample valve

  • Dirty sampling equipment, especially when samples are transferred from another sampling container

  • Sample bottle caps not being replaced immediately after the sample is taken

  • Dirty sample bottles

Second Scenario
Consider the laboratory method to obtain particle count data. Wearcheck operates an optical particle counter using the light blockage technique. This involves passing a laser beam through a controlled stream of oil, measuring the amount of light blocked by individual particles as they pass through the beam. Obviously, larger particles block more light than smaller ones, making size information relatively easy to obtain.

This method is sensitive and has some limitations. Particle count data is inflated by the presence of water droplets or gas bubbles in the sample because these are seen as particles. The laser cannot pass through dark or extremely contaminated samples, making them impossible to measure.

It is important to look at the appearance of the oil as well as other laboratory tests, such as water concentration and any comments based upon a microscopic examination, before reacting to an abnormal particle count result. It is also important to ensure that the sample is taken in the same manner and from the same sampling point each time a piece of equipment is sampled.

This consistency allows samples to be compared with confidence (compare apples to apples). Randomly sampling a machine from up and downstream of a filter can produce a confusing set of laboratory results if no sampling point information is included with the sample.

To summarize, set target cleanliness levels, achieve target cleanliness levels with continuous exclusion and removal of contaminants, and monitor contamination levels regularly to assure conformance to standards.

Benefits
Better lubrication leads to increased profits. Lubricants free from contamination provide better service to machines. Properly lubricated machines will provide better, more reliable and profitable service to the owner or operator. Why then is contamination control given such a low priority in most proactive maintenance programs?

This is largely due to a lack of understanding of contamination, its consequences and how to control it. Proactive maintenance requires a long-term investment in machines and people. A small amount of particulate contamination in a machine may not lead to an instant failure or halt operation today, but it will invariably shorten the machine's life. When the machine finally fails, it is difficult to determine or even prove loss of life due to particulate contamination.

Education is the most important step on a journey of successful contamination control. All personnel must be educated about their roles in the process and the benefits of reaching the destination. Teamwork is imperative and an educated, dedicated team will create an efficient, cost-saving contamination control program. The rule of thumb is that it costs 10 times as much to remove the particulate contamination than to prevent it from occurring in the first place.

The bottom line is this: Clean up your act and you will achieve greater machine availability and utilization. Reduced operating costs and increased profits will follow naturally.

About the Author

Michelle Allis is senior diagnostician for Wearcheck Africa, a member of the Set Point group. For more information, visit www.wearcheck.co.za.


About the Author