Liquid fuel storage failure & how to prevent it
Written on: July 14, 2020 by John Levey
This article is the first in a series on proper tank selection, installation and maintenance and is based on the National Oilheat Research’s Advanced Fuel Storage Tanks Gold Certification course and manual authored by John Levey, NORA, Director of Education and John Donohue, Special Projects Coordinator, Fuel Merchants Association of NJ and Donohue Associate, LLC The course and manual are available, at no charge at Learning.NORAweb.org
A properly installed and maintained storage tank is an extremely safe and efficient way to store power. A full 275-gallon tank holds over 34 million BTUs of potential heat in the fuel itself. This is equivalent to more than 11,000 kilowatts of electricity. All this energy is at the customer’s ready disposal day and night.
This on-hand power contributes to oilheat’s deserved reputation for comfort, cleanliness, safety and efficiency.
However, it is critical the storage tank be properly selected, installed and maintained. Also, homeowners must be aware that the tank is their property and their responsibility. Working with their fuel provider, they can be confident of many years of worry-free service.
Why do tanks fail?
Research shows that there are four primary reasons tanks fail. They are:
• On-site damage
• Transportation damage
• Manufacturing defects
(Either internal or external)
Internal corrosion is the main cause of above ground storage tank (AST) failures. The presence of water in the tank is a significant contributor to internal corrosion. Bacteria can live in the water as it feeds on the fuel in the tank. These bacteria produce biologically active sludge that can accelerate the rate of corrosion of the tank and other components from the inside. This is referred to microbial induced corrosion. Results of recent studies suggest the bacteria often excrete substances that are acidic. These substances can combine with moisture and form compounds that negatively affect fuel quality, the steel tank bottom and system components.
Keeping water out of ASTs will help maintain fuel quality, reduce the frequency of service issues and help prevent corrosion related component failures.
There are several simple things that can be done to reduce the accumulation of water in tanks:
• Drain water before installation. Tanks can accumulate significant amounts of water during storage and shipment even when tapping plugs are in place.
• Keep tanks full during the summer months. NORA’s research has shown that when ASTs are left less full over the off season, condensation is increased. Condensation can generate about 1 quart of water in tanks that are left ¼ full during the off season.
• Install tanks inside whenever possible. Outside ASTs accumulate significantly more water than inside tanks. As outside tanks are warmed during the day and then cooled at night, they accumulate water from condensation.
• Do not pump-over to new tank. Pumping fuel from the old tank into the new tank also transfers existing water and contaminants. It is best to schedule non-emergency tank replacements at a time when the tank being replaced will be less than ¼ full. This fuel needs to be disposed of properly. When larger volumes of fuel are present, or the replacement is being performed on an emergency basis, the use of a temporary tank on-site is advisable.
• Look for signs of water during service calls and tuneups. Inspect the filters, filter canisters, pump strainers and pump components for the presence or evidence of water, such as rust. Water in the fuel system is evidence of water in the tank.
Water is a primary contributor to tank corrosion.
Fills that are flush to the ground, fills with missing caps, broken tank gauges and vials are among the common causes of water entry. These situations should be corrected to ensure a watertight seal.
All the paste has changed color indicating that the water level may be higher than indicated. Paste should be cleaned off and reapplied to a higher level to determine the actual level of water in the tank.
Tanks installed with direct fill pipes, such as underground storage tanks (USTs) or ASTs installed outdoors, can usually be checked for water using a tank gauge stick with water indicator paste. When checking for water the burner should be off. Water finding paste should be applied to the bottom several inches of the tank gauge stick, adjacent to the side with the measurement increments. Whenever possible, a non-folding gauge stick should be used. Fully insert the gauge stick into the lowest part of the tank until it touches the bottom. Leave the stick at the bottom for about 30 seconds. The paste changes color to the height of any accumulated water.
With USTs, water accumulates due to mechanical failure of components such as fill caps, fill cap gaskets and vent caps. Less seldom, a broken or corroded fill or vent pipe may provide a means of surface water to enter.
Checking basement tanks for the presence of water is less straightforward In some cases, the tank is not pitched towards the bottom fitting and in other cases this fitting was plugged at the time of installation. Tanktop component removal to facilitate tank gauging should only be undertaken when evidence exists that water may be present (excess water in the filter, rust in pump cover or filter canister, etc.). Removal of tank top fittings requires those fittings be properly sealed after the gauging is complete to assure the tanks integrity.
When water is detected, every effort should be made to remove it or at least reduce the level. However, just removing the water is not the full solution. Anytime water is identified in a tank, it is important to inspect the entire tank system, identify how the water got in and advise the customer of recommended repairs.
External Corrosion is the main cause of failure of unprotected USTs. It occurs when the moisture and oxygen along with other elements in the soil lead to corrosion of the tank.
ASTs are also subject to external corrosion due to contact with walls, structures, soil, organic matter, etc. Manufacturers’ instructions provide valuable information regarding tank placement and recommended maintenance.
On-site damage is easily prevented when proper handling, installation and maintenance procedures are followed.
Some manufacturers suggest that damage during delivery and installation may be a greater cause of tank failure than corrosion.
To prevent the occurrence of onsite damage, tanks should be:
• installed in full compliance with manufacturer instructions and NFPA practices
• properly secured & supported
• protected from weather
• regularly inspected
Discovered defects should be corrected as soon as possible
This occurs when tanks are mishandled during transportation from the factory, warehouse and/or from the supply house to the job site.
To prevent transportation damage, tanks should always be secured during shipping and handled with care when being loaded and unloaded. When tanks are pushed along the truck bed or dropped from the truck, the tank’s structure can be weakened and the tank often suffers visible damage.
This accounts for the lowest percentage of oil tank failures. UL listed tanks are tested to ASME standards and most must pass a series of tests before being shipped. Thus, the majority of defects are discovered before a tank leaves the factory. The defective tanks identified through testing are not shipped to a distributor.
Preventing Premature Tank Failure
The best way to ensure tanks perform reliably is to make sure that everything is done correctly:
Tank type selection must be appropriate for its use and environment.
Secure tanks during transport to the job site and use the proper equipment to load the tank on the truck and place the tank in position at the job site to eliminate most transportation damage.
Installation must be in accordance with manufacturers instructions and all applicable codes and regulations.
A schedule of maintenance and inspection needs to be put in place and maintained.
Future articles will cover these and more. ICM