How to Prevent Water Accumulation in Oil Storage Tanks

  • OIL TANK WATER PREVENTION - CONTENTS: Avoid water leaks into oil tanks to avoid loss of heat or oil tank rust-through. Proper oil tank fill and vent pipe location keeps out water. Seal oil tank fill and vent pipes to prevent water contamination. How to prevent water condensation in oil storage tanks. How to keep ground water out of buried oil tanks. Did water in oil tanks come from a delivery of water-contaminated oil
  • POST a QUESTION or READ FAQs on how to keep water contamination out of oil tanks

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Prevent water contamination in heating oil storage tanks:

This article explains how to keep water out of oil storage tanks, both buried tanks (USTs) and above ground storage tanks (ASTs).

This article series explains the problems caused by water accumulation in oil tanks, how water gets into the oil tank, how to measure water in the oil tank, how to remove water from oil storage tanks regardless of whether the oil tank is indoors, outdoors above ground, or buried, and how to prevent water from getting into an oil storage tank.

We explain how to test for or visually check for water in a buried or above-ground oil storage tank, and how to get water out of an oil tank.

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How to Keep Water Out of Oil Storage Tanks

Photograph of an oil tank filler flush with the ground.Tips for Keeping Water out of a Buried Oil Tank

[Click to enlarge any image]

  • Water enters a buried or above ground tank by condensation: as temperatures vary moisture-containing air may be drawn into and then out of an oil tank.

    Air leaves the tank as oil is consumed; air enters and leaves the oil tank through the oil tank vent. Moist air entering the tank from outside can bring water which, on entering the cooler tank interior, condenses out of vapor form into water droplets which can, over time accumulate.
  • Water enters a tank filler pipe: from roof spillage onto the tank or filler top (particularly and obviously if the filler cap is left off), or from ground or surface runoff entering the oil storage tank (particularly and obviously if the filler cap is near, at, or below ground surface level).
  • Leaving off an outside oil tank filler cap for a few days is not itself a likely source of a problem unless the filler was exposed to heavy rain, roof runoff spillage onto the open filler pipe, or surface runoff entering the tank (such as for a filler pipe flush with the ground).
  • Water leaks into a buried oil tank from an actual tank perforation that admits ground water, or from a bad plumbing fitting on the tank. When oil levels in the tank is below an oil tank perforation or a leak in oil tank piping, it is possible for ground water to leak into a buried oil tank just heating oil may leak out of the oil tank when it is filled above the perforation or leak point.
Oil storage tank underground (C) Carson Dunlop Associates
  • Water leaks into the buried oil tank from a faulty filler cap gasket around the oil tank filler pipe plug, especially at installations whose oil tank filler pipe is located in a box whose top is flush with the ground surface.

    Rainwater or snow-melt water then enter the oil storage tank. The buried oil tank illustration (left) is provided courtesy of Carson Dunlop Associates. You'll notice that the oil tank is sloped away from the tank bottom oil piping connection, as we discuss below.
  • Water leaks into the buried oil tank from an oil tank vent pipe that is missing a cap to protect against rainwater or roof runoff spillage into the tank, especially if the vent (or filler pipe) are located under the roof's drip-line.
  • Water leaks into a buried oil storage tank from leaky oil piping fittings. R.W. Beckett recommends that [Quoting]
    All pipe fittings must be tightened securely and have the threads sealed with a resilient compound that can endure the environmental variables in temperature. Any loose or poorly sealed [oil tank fuel piping, fill, or vent piping] joints can permit ground water to infiltrate the [oil] storage tank.
  • Water is delivered to the oil tank along with the heating oil fuel: This is not common, but it is possible to get a delivery of "bad" heating oil that is water contaminated, especially if the oil truck happens to fill-up at the oil storage depot when an oil barge is unloading oil since during that operation water which is normally kept in the bottom of oil depot storage tanks may be stirred-up.

    Most oil companies know to avoid this problem and some also have water filters installed at their oil trucks. No oil company is going to admit that they picked up and delivered water-contaminated oil to your home so don't waste time asking them if they are guilty of this crime.

    R.W. Beckett referred to this [quoting] "possible but rare contributor due to storage and maintenance practices in the [heating oil] distribution system. Large bulk [oil storage] tanks must be checked for condensation accumulation and bled periodically.

    If this is not done conscientiously, then it is possible for water to be drawn out with the oil when the stocks are extremely low or when the bulk storage is filled and the water is forced into temporary suspension. Fortunately, our industry has implemented effective maintenance measures and this has been virtually eliminated. However, if water and sludge are found in a tank that does not have a leak, then it must be thoroughly pumped out, cleaned, and treated with a chemical additive that disperses water, sludge and neutralizes bacterial growth."

Tips for Keeping Water Out of Above Ground Oil Tanks

Above ground oil storage tank (C) Carson Dunlop Associates

As we discussed at ABOVE GROUND OIL TANK WATER ENTRY Sources of water entry into above ground oil storage tanks are similar to the UST water leak sources listed at BURIED OIL TANK WATER ENTRY. [Paraphrased, edited, and expanded from R.W. Beckett] :

How to avoid condensation inside outdoor above ground oil storage tanks:

[Items below are paraphrased, edited, and expanded from R.W. Beckett and other sources]:

  • Paint the above-ground outdoor oil storage tank silver (aluminum paint) to reflect sunlight (and heat), or locate the tank in a shaded area if possible.

    If you consider that in freezing climates we recommend constructing a heated enclosure around an outside oil storage tank to avoid oil tank waxing or water freezing and loss of heat, that step will also reduce the problem of oil tank water accumulation due to condensation.

    Also as we discussed at ABOVE GROUND OIL TANK WATER ENTRY, Outdoor above-ground oil storage tank water condensation occurs when a partially-filled oil tank is exposed to variations in outdoor temperature. Oil in the tank and the tank steel itself are warmed by sunlight and higher daytime temperatures.

Oil tank taking water (C) Daniel Friedman

  • Install properly sealed fill and vent pipes on the oil storage tank, and avoid locating the tank where roof runoff spills onto the tank or its piping (see our oil tank photo at left).
  • Install the oil tank so that the oil tank fill pipe end is sloped downwards. This will cause water entering at the fill pipe to pool right below the filler cap where it can be observed and pumped out.
  • For oil tanks drawing oil from the oil tank bottom, install a 3" vertical riser (soldering a 3" x 1/2" O.D. copper tube) onto the oil tank side of the oil tank bottom fitting so that oil is always drawn off from 3" above the tank bottom, thus above water that may be accumulated on the oil tank bottom (as long as the water has accumulated to a level less than 3" this works).
  • Install a water tank drain port on the lower end of the above-ground oil storage tank. [Properly installed a aboveground oil tank is installed with a few inches of slope away from the tank bottom outlet fitting so that water and sludge accumulate first away from the oil supply piping connection point.

    Even if the oil piping is installed through the tank top fittings (a better, more water and sludge-resistant approach), an oil tank bottom drain can still be used to check for and remove water accumulated on the oil tank bottom.

Oil tank piping through tank top (C) Daniel Friedman

  • Install the oil supply and return piping through oil tank top fittings rather than at the oil tank bottom fittings.

    A 3/8" or 1/2" diameter compression fitting is installed in a special dual-port oil tank top fitting that permits the copper oil supply and return piping to be routed through the tank top fitting, extending continuously (without potentially leaky joints) to 3" above the oil tank bottom. (See our photo at left.)

    R.W. Beckett's illustration shows that the oil pickup and return tubing are also bent at an angle away from one another so that the oil pick-up line does not pick up sludge or air bubbles that are caused by excess oil returning to the oil tank through the oil return line.
  • Keep the heating oil tank filled during warm weather. By minimizing the air space above oil in the oil storage tank you will reduce the oil tank air "exhale" as the oil tank warms, and "inhale" as the oil tank cools, thus reducing outside air and moisture being drawn into the oil tank.

This website provides detailed information about underground (buried) oil storage tanks (USTs), aboveground oil storage tanks (ASTs), above ground fuel storage tanks, reporting and cleaning up oil tank leaks, and choosing among oil tank leak testing methods.

We include detailed information about underground (buried) oil storage tanks (USTs), aboveground oil storage tanks (ASTs), above ground fuel storage tanks, reporting and cleaning up oil tank leaks, and choosing among oil tank leak testing methods.



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