A 200-litre drum (sometimes 180 litres) is one of the most common lubricant packaging types when purchasing lubricants. It is suitable for small to medium volume applications. Although it can come in plastic (high-density polyethylene – HDPE), steel drums are preferred for oil because of their durability in carrying hazardous goods.
Steel drums are designed so that the openings are on top, known as a bung, which allows for air venting as a pressure relief. Air can flow both ways as pressure changes in the air space above the oil surface in the drum. During warmer days, pressure inside the drum increases as the oil expands and pushes the air out. During cool night, pressure inside reduces as the oil contracts. When the pressure inside the drum is lower than the atmospheric pressure outside of the drum, air will be pushed in.
The bungs are sealed so that no liquid can exit or enter under normal situations. However, if a drum is stored upright and there is water on top of the drum (often the case if it is held outdoor), moisture via the highly humid air can seep through. This is due to powerful suction created from inside the drum especially at night when the ambient temperature is cooler.
This effect is known as drum breathing and is the leading cause of water introduced in a drum full of oil.
Generally, water in lubricants is never good unless it is for specific cooling or fire-resistant purposes. Besides affecting viscosity, water can do irreversible damage to the oil such as stripping out additives and increasing its acidity. Even when the water is removed via filtration, that damage is already done, diminishing lubricating performance and longevity. We should do all we can to keep water out from the oil drum.
The first thing is to store oil drums indoors or at least under shade, protected from the weather. The location also needs to be away from any potential water splashing or condensation such as a wash bay or a steam boiler. This way, chances of water accumulating on top of the oil drum is greatly minimised.
Due to space, financial and operational constraints, sometimes storing all drums indoors may not be possible. If storing outdoors is unavoidable, oil drums are preferably stored in a horizontal position so that the drum bungs would be at nine and three o’clock. This arrangement ensures the inside of the bungs are submerged in oil and act as a seal from air and moisture movement. You will need a drum racking and lifting equipment to do this safely and properly.
Perhaps the easiest but the least preferred way is through the use of drum cover. While storing the drums upright, one has to remember putting the cover on at all times. Drum covers can come in different types. There is one with an elastic ‘shower-cap’ while others are plastic moulded to size for more durability.
In short, the risk of storing oil drums outdoors and upright is water ingression which can bring lots of harm to the oil. Therefore, it is important for end-users to take steps to minimise the risk and prevent contamination in new oil.
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About the Author:
Aaron Said is ILD/Sinopec’s National Technical Manager. He is responsible for developing and delivering value-added lubricant technical services to client for reliability improvement, lubricant optimisation, and cost-savings. Among his professional credentials are Certified Lubricant Specialist (CLS) and Oil Monitoring Analyst I (OMA) from Society of Tribology & Lubrication Engineers (STLE) and the International Council of Machine Lubrication (ICML)’s Machine Lubricant Analysist I.