Long-Term Storage Package for Diesel Fuel
The useful life of diesel fuel ranges from six months to 10 years, depending on storage conditions and maintenance practices. In general, the keys to longer useful life are to keep the fuel dry, clean and cool. More specifically:
- Storage conditions – Minimize exposure to the greatest threats to fuel quality and fuel stability, specifically: water; air; light; heat; and certain reactive metals.
- Maintenance practices – Implement and maintain recommended policies and procedures designed to counteract the effects of these threats.
A brief description of the major threats to stored diesel fuel, their adverse effects, and recommended remedial actions to minimize their effects appears below.
- Brief explanation – Stored diesel fuel naturally attracts water. The main source of water in storage tanks is condensation caused by process commonly known as “tank breathing.” The rate of condensation depends on local climate: higher in hot, humid, coastal areas; and lower in cool, dry inland areas.
- Adverse effects – Water promotes the growth of various microbial organisms, primarily algae, fungus and bacteria. Excess microbial growth can have several adverse effects, including:
- Engine performance – Algae, fungus and bacteria can clog fuel filters and fuel lines, causing the engine to run poorly, or not at all.
- Fuel stability – Microbes emit acidic by-products that decrease fuel stability.
- Tank corrosion – Microbial by-products contribute to tank corrosion.
- Remedial actions – Recommended maintenance practices to minimize the presence of water in storage tanks include:
- Drain water from storage tanks weekly. Extend drain interval if storage tanks show little or no tendency to collect water, but no longer than once a month.
- Drain water at a well-defined low point in the storage tank (such as a cone down bottom) where water tends to collect.
- Keep storage tanks full. Excess tank capacity promotes condensation, as there is air in the tank & water in the air. Excess capacity also promotes corrosion of the exposed, dry, interior walls of the storage tank above the fuel line.
- Use biocides to prevent and eliminate the types of microbial growth commonly found in finished diesel fuel. Biocides also prevent the biodegradation (reduction of fuel quality caused by microbes) of crude, refined and feedstock oils and fats (such as poultry, soybean, aromatic, paraffinic and naphthenic) during storage.
- Brief explanation – As a carbon-based petrochemical, diesel fuel begins to oxidize as soon as it leaves the refinery. The oxidation process begins when hydrocarbons in the fuel are exposed to oxygen in the air. This exposure sets off chain reactions that turn healthy, stable molecules in the fuel into unstable, reactive molecules.
- Adverse effects – These chain reactions cause the fuel to darken and stratify, and they produce fine sediments and gums that can have several adverse effects:
- Less effective fuel filtration – Sediments and gums clog fuel filters, initially starving the fuel and ultimately stopping the engine. Frequent filter changes are required to keep the engine running.
- Less efficient fuel combustion – Sediments and gums do not burn very well.
- Carbon and soot deposits – Deposits can damage fuel lines, fuel filters, fuel injectors, and other system components.
- Remedial actions – Recommended maintenance practices to minimize the adverse effects of oxidation on stored diesel fuel include:
- Remove sediment & gums from fuel by filtering contents of main storage tank through a recirculating filter system. Check & change the filters at regular intervals. Turn fuel over when interval reaches a certain frequency.
- Use antioxidants to prevent or impede oxidation by interrupting the chain reactions at the start of the oxidation process.
- Use fuel stabilizers to prevent harmful oxidation reactions and acid-base reactions in a similar way. Fuel stabilizers react with acidic precursors in the fuel to prevent them from reacting with other fuel agents.
- Brief description – Certain reactive metals catalyze and accelerate chemical reactions which decrease fuel stability. These metals include: copper; iron; zinc; and metal alloys containing those metals (such as brass). Contamination by dust and dirt
Adverse effects –
- Decreased fuel stability
- Remedial actions – Recommended maintenance practices to minimize the adverse effects of these reactive metals on stored diesel fuel include:
- Avoid contact with surfaces containing these reactive metals.
- Prevent contamination by dust and dirt, which may contain trace elements of reactive metals.
- Use metal deactivators to prevent reactive metals from reacting with the fuel.
The primary method for estimating the useful life of diesel fuel is ASTM D2274: Oxidation Stability of Distillate Fuel Oil (Accelerated Method), more commonly known as “accelerated stability.” This test measures the amount of gum and sediment deposited after storing fuel at 95°C in the presence of oxygen for 16 hours. These results correspond to those produced by storing fuel at 25°C for one year. The acceptable limit is 20 milligrams of gum and sediment per liter of fuel.
Long-Term Storage Package for Diesel Fuel
|#||Test Name||ASTM Method||Units of Measure||Limits by Grade|
|1||Flash Point||D93||° Celsius||38° min.||52° min.||55° min.|
|2||Water & Sediment||D2709||% by vol.||0.05% max.||0.05% max.||0.50% max.|
|3||Distillation||D86||° Celsius||288° max.||282° –338°||N/A|
|(A) S15||D5453||µg / gram||15 max.||15 max.||N/A|
|(B) S500||D2622||% by mass||0.05% max.||0.05% max.||N/A|
|5||Cetane Index||D976||Cetane Index||40 min.||40 min.||N/A|
|6||Cloud Point||D2500||° Celsius||Report||Report||Report|
|7||Pour Point||D97||° Celsius||Report||Report||Report|
|11||Accelerated Stability||D2274||mg. / liter||20 max.||20 max.||20 max.|