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Oil Tank Leaks or Oil Tank Failure Causes - oil tank leaks are caused by corrosion, damage, soil conditions, other factors
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• Causes of leaks in oil storage tanks

This document explains the common reasons for oil tank leaks in or from home heating oil storage tanks. Both underground tank leaks and above ground storage tank leak causes are discussed. Oil tank leaks are caused by corrosion, mechanical damage, soil conditions, other factors which are explained here. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

FAILURE MECHANISMS - Fuel or Heating Oil Storage Tank Failure Mechanisms

External oil tank rust, unless very heavy, isn't highly correlated with internal rust, corrosion, and tank leaks. Most oil tank failures are due to rust perforation from the inside of the tank. This means that if you see any indications of even a pinhole or leak on an oil tank, be careful! The steel may be quite thin and can be easily punctured even though from outside it may look pretty good.

RUST PERFORATION - Usual Reasons for Oil Storage Tank Leaks - Rust Perforation

Underground fuel storage tanks usually fail from rust perforation from the inside of the tank, due to several effects of water inside the tank including, in the case of heating oil, combination of water with sulphur in the fuel.

So if a test shows that there is a lot of water in a buried oil tank one would be more pessimistic about its remaining life.

Water in home heating oil joins with sulphur in this case to become acidic and corrosive. It causes tank failure by rust penetration from the inside. Also, there may be a bacteria living in tanks, existing at the water/oil interface, digesting organics and excreting acids.

The corrosiveness of this activity is often most significant at the water-oil interface in the tank, which explains why some tank leaks will develop not at the very bottom of the tank (but look there too) but instead, a few inches up, along the side of the tank.

The height of this corrosion line along the sides of the inside of the oil storage tank depends on the amount of water in the tank and thus the location of the water/oil interface line on the side of the tank.

HOW WATER GETS IN - How water gets into an oil storage tank

Bad oil tank filler location

Water, enters a heating or fuel oil tank from a poorly sealed fill box which is flush with the ground or which is located below a roof edge, from missing fill pipe or vent pipe caps, from loose pipe fittings, and less commonly, from water delivered with fuel from an improperly maintained bulk storage facility.

Condensation inside oil tanks and groundwater leaks into oil tanks

In outside above-ground tanks water also often enters the fuel oil tank from condensation as temperatures change, particularly when the tank is not kept filled. Above ground tanks in cold climates may be exposed to temperature variations drawing and expelling air from a partly-empty tank. When warm moist outdoor air is drawn into a steel tank, moisture in the air may condense and accumulate in the tank.

Water can also leak into a tank from ground water when the oil level is low if the tank is damaged. [R.W. Beckett Corporation, Technical Information Bulletin, October 15, 1990.]

Delivery of bad oil

Most oil delivery companies store their product in very large storage tanks near a rail or waterway delivery point. Large oil storage facilities may deliberately keep water in the bottom of those tanks so that if the large (above ground oil storage depot tank) begins to leak, water will leak out first and thus be observed before there is a large oil spill. An oil truck which is filled when oil has just been delivered to the oil depot tank might in unusual circumstances pick up excessive amounts of water in the oil it obtains, thus potentially delivering it to its customers. Equipment is often used to attempt to trap and filter water in oil and other fuel delivery systems to reduce this risk.

IMPROPER INSTALLATION - Improper oil tank installation can cause leaks

Placing a tank in cinders or ash or acidic soil: tanks set in beds of cinders or ashes cause outside-in corrosion and leaks.

Tanks may also be damaged by being dropped or pushed into the excavated hole rather than being carefully lowered by a rope.

Burying an indoor-rated tank: That an installer would bury an indoor-rated 275-gallon tank outdoors may come as a surprise to some readers but I've been surprised at how often we've found either completely or partially buried indoor-tanks.

At least on older oil tanks (perhaps before 2000), the UL label affixed to the tank explicitly says "indoor use only" right there for the installer to read. I contacted a few manufacturers and wrote to UL to ask if it was a building code violation to bury a tank with this indoor use rating. I haven't received a reply, but interestingly, newer 275-gallon steel oil storage tank UL rating labels simply dropped the wording that indicated where the tank could be used. Our concern was that an indoor-rated tank may lack the thickness of steel or an anti-corrosion coating that a buried tank needs.

Placing an indoor-rated tank outside with no weather protection also risks water entry in the tank (from roof spillage or condensation), gelling of the oil and loss of heat in cold climates, and perhaps extra corrosion.

MECHANICAL DAMAGE - Mechanical damage to oil storage tanks

oil tanks may be damaged during their installation, such as being dropped or gouged against a rock or other item which scratches or dents the tank, increasing its vulnerability to outside corrosion.

While it's speculative (we have no field data on this item) tanks or tank piping may be damaged by vehicle traffic in some locations as well.

IMPROPER PIPING - Improper oil piping can cause leaks

Oil tank piping materials or connections can lead to oil leaks. If you didn't know, residential oil tanks are usually filled under pressure. The oil filler nozzle is actually linked to the top of the inlet pipe and the truck pumps into the tank at pressure - most-likely to speed the delivery process. This fill-pressure can be considerable and can cause leakage or even catastrophic tank failure and leaks into a building if the tank piping is improper or if the tank is damaged.

• At an above-ground or indoor oil storage tank a small amount of seepage around the oil filler pipe is normal - having installed oil piping the author testifies that it requires very good workmanship to avoid this seepage as the tank top thread tapping and 2" steel pipe thread tapping can be a bit crude. If oil is running down the tank onto the floor or causing an odor problem this connection needs to be re-made. Because the work can be troublesome (a filler pipe disassembly may require demolition at a house wall) it should not be done unless really needed.
• At a buried oil storage tank loose or improper oil filler connections at the top of a buried tank or anywhere in the piping run can leak onto outdoor soil (luckily usually not deep underground) or indoors in a building.
• Under-sized fill or vent piping can cause leaks inside or out, including catastrophic oil leaks if a (plastic) pipe breaks.
• The most catastrophic in-building oil storage tank leaks are not from rust perforation itself as such leaks are usually slow drips. Extreme indoor oil contamination occurs in more unusual and very serious circumstances when indoor oil tank has been removed from a building, for example on conversion from oil to gas heat, but the oil filler pipe was left outside and through the house wall, though no longer connected to a tank inside. In an instance in Ulster County, New York, the contractor left plywood outside nailed against the building to prevent access to the old filler pipe pending its removal. But a neighbor called her oil company with an out-of-oil "no heat" condition in very cold weather. The oil delivery driver, intending to assist in an urgent case, went to the wrong house, removed the plywood, and pumped hundreds of gallons of oil directly into the home's basement.

SOIL CONDITIONS - Soil conditions as a contributor to buried oil tank failure

If a soil is acidic and particularly in areas where there is also a lot of groundwater or surface or roof runoff around a buried oil tank, the corrosivitiy of the soil may be a factor in oil tank external corrosion and ultimate leakage

Manufacturing defects: such as defects in the coating of a steel tank to be buried or poorly-welded seams may result in underground oil leakage. I have not seen reports of this occurrence - this may be a theoretical rather than a significant risk.

More Information on Oil, Gas, or other Fuel Storage Tank Hazards, Testing, Reporting, & Environmental and Building Diagnostic Inspections and Repairs

• Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
• Abandon a Buried Oil Tank, How To - Abandoning Commercial Underground Tanks, Russ Brauksieck, ASHI Tech. Journal, Vol.3 No.1 Spring 1993, P. 40-41 [Reprint]
• Above Ground Oil Tanks: Visual Inspection of Oil Storage Tanks for evidence of leaks, damage, improper piping - photos and text
• Above Ground Oil Tanks Checklist, an Oil Company's advice
• Above Ground Tanks UL Standards, UL Tank Listing Standards, guidance for home owners, buyers, and inspectors
• Buried Oil Tanks - Finding How to Find Buried Oil Tanks and "Nearly Hidden" and Leaky Oil Tanks - photos and text.
• Buried Fuel tank - Advice - Buried FUEL Tank - GAS or OIL advice for home buyers, inspection report language
• Environmental Issues & Regulations for Oil Tanks, Registration, Abandonment, Leak Reporting
• Home Inspection Report Language Library: Buried Oil Tanks, Basic home buyer advice - home inspection report language suggestions
• Home Inspection Report Language Library: Visible Defects in Oil Tank Installations, Tanks, and Heating Oil Piping
• Home Inspection Report Language Library: Gas Fuel Piping or Tank Faults Basic advice - home inspection report language suggestions
• Home Inspection Report Language Library: Oil Tanks text file list © Oil and Other Storage Tank Leaks, Testing, Abandonment, Inspection - UST home inspection report language files - Reference List
• Indoor Environment Website Indoor Building Environmental Hazard Detection, Testing, Repair, & Prevention - Main Web Page
• Leaky Heating Oil Tanks - Advice for Home Owners or Buyers: caused of leaks in oil tanks, oil tank testing alternatives, what to do about leaky tanks: D.J. Friedman, ASHI Tech. Journal, Vol.2 No.1, Winter, 1992 p. 42-43 Illus
• Leak or Failure Rates for Home Heating Oil Tanks
• Legal Issues Regarding Buried Oil Storage Tanks K.S. Rea, Attorney, summary from ASHI Chapter Seminar.
• Primer on Petroleum Bulk Storage Tanks & Petroleum Contamination of Property Paul H. Ciminello, ASHI Tech. Journal, Vol.3 No.1 Spring 1993, p 35-39
• Petroleum Bulk Storage J. Sibblies, NY State DEC, Advice to Home Owners and Home Inspectors about Oil Storage Tanks - summary from ASHI Chapter Seminar.
• Septic Tank inspection, testing, diagnosis, repair
• TANK FAILURE CAUSES - Oil Tank Failure Causes - oil tank leaks are caused by corrosion, damage, soil conditions, other factors
• TANK TESTING - - How Oil Tanks are Tested for Evidence Leaks, of Current or Previous Oil Spills
• TANK FAILURE RATES - Oil Tank Failure Rates - Oil Tank Leak Probability as a Function of Tank Age, Location, Condition, Soil Conditions and Other Factors
• Web Link Exchange: Contact Us to list your website or contact information for oil tank testing, tank corrosion research, oil industry experts

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