Locating Heating Oil Storage Tank Leaks
Where do leaks occur in heating oil storage tanks & what causes them?

  • OIL TANK LEAK POINTS - CONTENTS: Most common locations of leaks in oil storage tanks & piping systems. What causes a leak in an underground oil storage tank? What causes leaks in above ground heating oil tanks?
  • POST a QUESTION or READ FAQs about the cause, detection, and repair of leaky oil storage tanks at residential & light commercial properties

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Causes & locations of oil storage tank leaks:

This article describes the causes of leaks in buried oil tanks and above ground oil storage tanks and the common points at which oil storage tank leaks are most likely to be found.

Water may leak into oil storage tanks, or may enter tanks by other means; oil such as heating oil or fuel oil may leak out of oil storage tanks, risking a costly environmental problem.

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What are the Causes of Oil Tank Leaks & Spills?

Oil storage tank leak on tank bottom (C) Daniel FriedmanAt least some of these causes of oil leaks or spills can be avoided by simple inspection and maintenance. The modest oil spill shown in this photo could have been avoided by properly sealing the brass oil line fittings at the bottom of the oil storage tank.

[Click to enlarge any image]

On an outdoor or buried oil tank a leak like this could go un-detected for many years and could form a more serious oil spill.

This is a chapter of our "Heating Oil Underground & Above ground Oil Storage Tank Leaks, Testing, Problems & Solutions, Home Buyer's / Home Owner's Guide" which offers extensive free un-biased oil storage tank inspection and testing advice for property buyers and owners.

In-Tank corrosion: Underground fuel or heating oil storage tanks usually fail from rust perforation due to several effects of water inside the tank including, in the case of heating oil, combination of water with sulphur in the fuel, bacterial action, and other factors.

External rust, unless very heavy, isn't highly correlated with internal rust. Leaks can occur due to tank damage or at piping connections.

Oil Tanks in Corrosive Soils: Oil storage tank leaks are more likely if a steel tank has been buried in corrosive soil or if the tank was damaged during installation, such as gouging it or bouncing it off of a rock as it was placed into a hole for burying.

Oil Tank Piping Leaks: Oil tank leaks may occur at buried piping connections as well.

Delivery Oil Spills: occur around the tank fill pipe and range from trivial to more extensive requiring soil removal and cleaning. These leaks are usually obvious at the ground surface around the oil tank or tank filler.

Inadequate fill or vent pipe diameter is blamed by some for leaks at buried or above ground oil tanks, asserting that because oil tanks are filled under pressure from the oil delivery pumper-truck, a corroded, damaged, or poorly-plumbed oil storage tank, or one with a too-small vent opening, may not withstand the pressure of the filling process.

Indoor oil spills during tank fill or later from a leaky oil tank range from trivial local cleanup and deodorizing efforts to very serious contamination problems if an oil tank bursts during oil delivery (which I suspect is rare) and on occasions when an indoor oil tank has been removed but someone (some fool) has left the oil filler pipe installed on the building, and when subsequently an oil delivery is mistakenly made through the filler pipe onto the empty basement or crawl space floor. This may sound crazy but it actually happens.

Home buyers should be sure to review OIL TANK LEAK TEST METHODS - Leaky Heating Oil Tanks - How Oil Tanks are Tested for Evidence Leaks, of Current or Previous Oil Spills and OIL TANK LEGAL ISSUES - home Buyers and Home Owners Guide to Leaky Heating Oil Tanks - What to Do About & When to Report Oil Tank Leaks. Leaky Heating Oil Tanks.

Home owners who have old oil tanks above ground or any age oil tank below ground should also be sure to review OIL TANK ABANDONING PROCEDURE - Abandoning Commercial vs. Residential Underground Oil Storage Tanks (UST) - Procedures & Regulations A separate website addresses Septic Tanks.

What are the most-common sources of heating & fuel oil leaks in storage systems?

Question/Comment: researching statistical data on percentage of leaks in oil piping systems vs. leaks in oil storage tanks

Leaky heating oil pipe connectors (C) Daniel Friedman 2010I am searching for reliable information on statistical data about the percentage of leaks in suction piping systems, considering USTs before USEPA Regulations (80’s), in comparison to leaks in USTs.

I have worked for Shell in Brazil for several years, our petroleum regulatory agency has no data on it, and the state environmental regulatory agency has no data either.

If there is any link or peace of good information that you van lead me to it, I will appreciate the indication.

[Photo at left by illustrates leaky flange and brass-to-steel threaaded adapter at an oil burner]]

Roberto Abdalla Concré-S Gestão Empresarial
Diretor de Meio Ambiente

Reply: some reasons for lack of early UST, AST, & fuel or heating oil piping leak data

OIl tank inspection (C) D Friedman S Vermilye 2009Siento que eo não falo portugés Sr. Roberto but discussing in Ingléa, you raise a very interesting oil leak data question for which I have not seen nor been able to find satisfying data; but as I'm not an expert researcher on the topic, we can probably find some credible research - perhaps via Google Scholar or from other industry experts.

Previously I have reported on old data on oil tank leaks in the northeastern U.S. - that original data at the source (Fuel Oil & Oil Heat Magazine) subsequently seemed to disappear from public view though the publication itself continues. (OIL TANK LIFE, ABOVEGROUND)

We might approach EPA and other sources to see if there is funding to finance a well-designed study. However as later discussion and comments from both of us will make clear, there are some uncertainties about just manyreports of oil storage system leak rates & occurences, even though leak reporting is mandatory in some countries (such as the U.S. EPA regulations to which you refer.)

As a property inspector alert for signs of possible UST or UST piping leaks over some years I developed some opinions about clues one might see that would raise a red flag and call further testing.

Because of the occasional very large oil spill cleanup costs involved, I and surely other field investigators encounter questionable situations (to put it politely) where a property owner or even an oil delivery company knew that leaks had occurred but didn't want to report that condition.

At a few inspections the property owner basically threw us off of the land rather than permit us to even raise a question about the possibility of underground oil storage tanks, and in other cases clients reported that a seller would not permit leak or contamination testing.

Such oil contamination problems linger until the property is sold and the new buyer, being diligent, has some inspetions and tests performed. Some of my advice to property buyers is at OIL TANK, BURIED, ADVICE.

Follow-up & Discussion about the most-common sources of heating & fuel oil leaks in storage systems

Table of types of leaks in underground oil storage tanks - Missouri PSTFStudy Reports Sources of Underground Oil Storage Tank Leaks

R.A. -> D.F.

I have done some library search and found a very interesting study from the Missouri Petroleum Storage Tank Insurance Fund [8][23][24][25][29] (figure at left) and some additional data from Maryland [30].

[Click to enlarge any image]

[Underpinning the data shown at left, the PSIF has insured 7093 oil storage tanks thorugh December 2012, has paid 1061 claims and has 421 outstanding. Ed. - Source MIssouri PSIF Facts & Finances Decembe 2012][8]

Those two studies make sense to me and are well aligned with my initial perception and personal experience.

Steel piping failures are harder to detect especially when we consider hand stick measuring systems and no automatic reconciliation procedures as it was by the eight´s.

In Brazil, we started moving from steel piping to HDPE in 1994 and by 1996 100% off all new installations were made off HDPE pipes, HDPE sumps, etc.

In general, we do not use pressure lines and we can consider that all of it is based on suctions systems (Tank/Pump System) with check valves.

Reply: DF -> R.A. - About the the most common UST, AST & Oil piping leak points,

Documented in more detail at OIL TANK LEAK POINTS it is my OPINION that

Plastic coated L copper heating oil piping (C) Daniel Friedman 2013For oil piping leaks, soil chemistry, movement, mechanical damage are most common problem causes if we exclude poorly made pipe joints;

Poorly made pipe joint leaks probably occur more often than piping damage leaks along the length of the pipe itself, though flexible copper oil piping widely used at residential UST and AST installations can be leaky from corrosion and abrasion. That's surely why new residential oil piping is usually installed using HDPE-covered flexible 3/8" or larger L-copper.

A very common leak at above ground tanks that I see is around fill, vent, and fuel level gauges - particularly where deliveries are of large tanks (the driver walks away to smoke a cigarette and fails to stand by the fill pipe listening for the tank alarm to indicate that the tank is full) and in very cold weather (the driver retires to sit in the warm cab of the tank truck);  I also see leaks due to overfilling when the tank alarm (whistle) is not installed or not working; I've published details about oil piping leaks at OIL TANK PIPING & PIPING DEFECTS.

But I've not found statistical data on these occurrences nor their rates before and after various regulations are enacted.

Short of a funded study, we could of course informally poll oil delivery companies but I'm not optimistic that the data will be so accurate; oil leaks, spills, and cleanups are controversial and bad publicity for the oil industry, making for under-reporting at every opportunity; Those reservations make reports such as the one you fouind, from the insurance industry, all the more interesting and important. It is always useful to understand differences of practice among countries;

About not using pressure lines for oil piping, in North America (U.S. & Canada) larger heating systems and commercial processes using oil heated boilers & equipment often use NO. 6 heating oil - very thick dirty fuel that can only be moved successfully to the burner by a combination of heating and a pump system. There is still a vacuum type pump at the oil burner, but pressure-piping may be used to circulate and heat oil; And on a two-pipe oil line installation, a return pipe from the fuel unit (oil burner pump) takes excess oil back to the oil tank - that line is under pressure, not vacuum, when the burner is operating.

How do we prove that an oil tank is not leaking

The Missouri PSIF lists the following seven methods that the insurance fund will accept as evidence that a fuel/heating oil storage system is not leaking - listed just below, but because these tanks address different environments and kinds of potential leaks it's not clear to us that any single test is a complete guarantee about oil leaks:

  1. Automatic Tank Gauging (ATG)
  2. Stastical Inventory Reconciliation (SIR)
  3. Interstitial Monitoring (IM)
  4. Daily Inventory Control & Annual Tank tightness Testing (DIC)
  5. Vapor Monitoring (VM)
  6. Groundwater Monitoring (GW)
  7. Manual Tank Gauging (MTG)
  8. - Source MIssouri PSIF Insuring Tanks [8]

Reply: R.A. -> DF: further research on & field experience reports of sources of fuel oil & heating oil leak points

I could not agree more with your opinion about why [heating oil] pipes leak. Back in 1989, when I started working with gas stations, USTs & heating/fuel oil pump installations, every piece of pipe was made of steel and all joints were threaded. The biggest steel length used at that time was 6 meters, and a typical connection line between UST and pump was about 10 meters[ - requiring multiple connections, where more connections means more leak risk].

As an average, we can consider that those connection lines had about 10 to 12 threaded connections (Joints, curves, elbows), or potential leak points; and as you very correctly said, mechanical stress and poorly made services caused most of the leaks.

At that time, those[oil piping, tank to appliance] connection lines had no check valves; instead we used foot valves, turning [oil] leak detection an enormous challenge considering that leaks were of a very small in instantaneous volume, constant in duration and random in location.

Statistics about leaking points are very hard to find and the reason is quite simple

  1. First, nobody likes to talk about it. When a leak was found at that time all effort was made to fix the situation as fast as possible and a little or no attention was given to the reasons why the leak occurred.
  2. Second, we had no tightness test companies like in the US working in Brazil and the UST installation companies handled all UST testing services with pressure tests or hydrostatic tests. This system was not accurate and those companies generated no data.
  3. Third, our first legislation about tightness test started back in 1992 and the first major testing program started in 1994. Once again, all data generated at that time was lost. We were moving fast to HDPE, so every leaking steel pipeline found had to be changed by a new HDPE pipeline and a check valve have to inserted on the system in substitution to the foot valve. In fact, some companies decided that if there was any line leaking at the gas station, all pipelines have to replaced, using HDPE.

Taknology was one of the first companies to start a successful local operation and they really did an outstanding job. Several others came and then the market exploded for the UST tightness test segment until late 1990´s.

By 2000 no more steel pipes were allowed in gas stations in Brazil and all old ones were under conversion to HDPE with suction systems, as it is today. I took part in this study - it was very informative. I will be continuing to dig around for data on oil leaks.


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If your oil tank is leaking see OIL TANK LEAK ADVICE.

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