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OIL STORAGE TANKS - home
ABANDONING OIL TANKS
ABOVE GROUND OIL TANK (AST) GUIDE
BURIED OIL TANK (UST) GUIDE
HEATING OIL TYPES & PROPERTIES - home
HOME BUYERS GUIDE TO OIL TANKS
OIL SPILL CLEANUP / PREVENTION
OIL TANK ABANDONING PROCEDURE
OIL TANK INSPECTION & TROUBLESHOOTING
OIL TANK LEAKS & SMELLS
OIL TANK PIPING & PIPING DEFECTS
OIL TANK REGULATIONS
OIL TANK REMOVAL COs
OIL TANK SPILL CLEANUP / PREVENTION
OIL TANK LEAK TEST METHODS
OIL TANK TESTING & REMOVAL COs
OIL TANK WATER CONTAMINATION
Guide to types of oil storage tank leak tests available:
This article discusses the types of oil storage tank tests that may be performed on buried oil tanks and above ground oil storage tanks to check for leaks or imminent leaks. Not all storage tank tests are equal in accuracy nor cost, and some are more appropriate than others, depending on other factors.
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Oil tank leak testing guide: this document describes the common methods used to test oil storage tanks for evidence of leakage, either by soil testing, pressure testing of the tank, or by other tank screening measurements.
[Click to enlarge any image]
Other steps to locate and test heating oil storage tanks at properties, both buried tanks and above ground tanks are discussed at other documents at this website.
Leaking oil tanks are not only a concern as contaminants of the water supply, but have become an increasing general environmental concern addressed by the DEC. Leaking commercial oil storage equipment and even simply-suspect oil storage equipment have been extremely costly to address.
Such burdens were never anticipated when the equipment was installed. While similar regulations pertaining to residential installations are scarce, this topic is of growing concern to home owners and home buyers.
Look for yourself: Before deciding to hire a tank testing company for professional inspection and testing, some basic information such as the age (property and tank), tank location, and type of oil tank, and for above-ground tanks, a simple visual inspection of the tank and its piping, can give you and idea of the risks involved.
Look for obvious leaks such as oil stains on the ground or floor under or around the tank and around the oil fired equipment. Remember to look under the oil tank at its bottom, as most leaks occur in the lower portion of the tank.
The leaky oil storage tank shown at left is discussed
Hire an expert: Specialty companies and some oil companies have equipment to test buried tanks for leaks. Soil testing, simple low-psi pressure-testing and sophisticated electronic testing are commonly used.
I advise home buyers to have a soil test performed rather than a pressure test of an existing oil tank, since even if the tank is not currently leaking we would prefer an assurance that it didn't leak before, say from a plumbing connection that was repaired.
Many storage tank testing companies also offer storage tank removal and site cleanup services as well.
From a previous use, a buried oil tank may be present or may have been present at a property now served by an indoor, above ground oil tank or even by LP or natural gas.
So don't assume that because you don't see a tank that none was ever used or present at a property.
OIL TANK LEAK TESTING METHODS - How Oil Tanks are Tested for Evidence of Leakage
Testing for water in an oil tank (above ground or buried) is simple and can be done by any service person. Tank testing methods for oil leaks or for the risk of oil leakage vary in risk to the tank, cost, invasiveness, length of time to complete, and more.
In addition to oil tank inspection, oil piping inspection, and oil tank testing to "pass" or "fail" an oil storage tank, more sophisticated tests are available to assess the chances that an existing heating oil storage tank has leaked or is likely to have a serious leak soon.
These include a oil tank corrosion analysis which adds to the basic tank inspection and tests an assessment of the level of corrosion of the tank walls and thus the chances of its leaking or failure, and soil corrosion or soil corrosivity evaluation which includes an evaluation of soil samples collected from around the tank in order to assess the degree to which the soil in which the oil tank has been buried will contribute to the process of corrosion of the (presumably steel) buried oil tank.
Specialists and some oil companies have equipment to test buried tanks for
leaks. Both simple pressure-testing and sophisticated electronic testing are
used, mostly on commercial equipment, and more recently on residential tanks.
Testing for water in the tank is simple and can be done by any service person
using a simple chemical paste on a probe. A lot of water in the tank is a reason
This test for oil tank tightness developed by Mesa Engineering, uses a digital probe and using ultrasound, examines frequency changes to detect a leak in the oil tank or its piping.
The Mesa 2-D Digital test includes a "U-L" frequency leak test that detects leaks in the oil tank or its piping. The Mesa 2-D test also detects vapor bubbling ("P-L" frequency leak) indicating that the oil storage tank or its piping contains a leak in the oil piping or oil filler piping portion of the system.
This is a low "negative pressure" or vacuum test using a vacuum of 60 inches of water or –2.16 psig. The manufacturer requires that test operators be certified at least every two years.
According to the developer, Mesa Engineering, a U-L frequency leak typically occurs in the oil vent pipe or fill pipe, and can often be repaired, while a P-L frequency leak usually indicates a critical system failure that means the tank will probably be taken out of service and abandoned.
Watch out: In reader correspondence we have a report of an owner's concern about an apparent "coincidence" that within two weeks following a Mesa 2-D oil tank test a catastrophic oil tank leak was found and a costly cleanup followed. Not only is the Mesa 2-D oil tank test considered "safe" (it does not expose the oil tank to high pressure or high vacuum), but a review of the Mesa 2-D tank test report for this case disclosed that the test itself detected a tank failure.
Our OPINION was that provided the test was conducted properly, the most likely explanation of the apparent coincidence was that the test had correctly detected an oil tank leak that was not previously recognized, and that had existed for a considerable time.
Mesa 2-D Oil Tank Test Report Example #1 - see this example of a Mesa 2-D oil tank leak test that found significant evidence of an oil tank leak. The owners reported that within two weeks a major oil leak was confirmed and a cost underground oil tank replacement and oil spill cleanup was required.
The company who conducted this test, ATS Environmental Services Co., includes in their Mesa 2-D test description
Mesa Oil Tank Test Report Example #2 - this example of a MESA oil tank test also found that the tank was leaking. As we pointed out to the reader who contributed this oil tank test report, the test found a tank leak, called for appropriate repair action, and did not (indeed could not) indicate the extent of soil contamination that may be present.
Interpreting a MESA 2-D oil tank test report
In the example MESA 2-D oil tank leak test Mesa Oil Tank Test Report Example #2 the test company recommended that possibly leaking oil piping be inspected and repaired if found faulty (though it appears that the technician didn't think that was the problem. The company continues to indicate that if piping repairs do not stop the leak, the tank will need to be abandoned according to proper procedures.
OPINION-DF: even if the oil piping is repaired and the repairperson believes that a leak was fixed, there is a potential for significant increases in the later cost to abandon the oil tank if in fact it continues to leak, and because there can be multiple leak defects in any tank and piping system (so that fixing one may not fix them all). For that reason, a follow-up test might be appropriate.
Mesa 2-D Method with ACT v1 Water Level Sensor - test description and specifications from Mesa Engineering - web search 6/22/2010. Mesa Engineering, 5801 Dierker, Houston TX 77041 713-895-7000, [company website link in this literature is not functional]
Using this tank testing method the oil tank is sealed and pressurized to a low psi level, then carefully monitored for a pressure drop, perhaps for 24 hours. This method is comparatively quick to execute but I don't care for it.
Notice (in our photo at left) that some oil tank manufacturers do not want their oil tanks pressure-tested after the tank has been installed.
Details are at OIL TANK PRESSURE.
Some home owners balk at this test, fearing that the pressure of the test procedure will "burst" an oil tank that is about to fail. I am doubtful that this is a legitimate concern. The pressure at which the tank is being tested is almost certainly a much lower psi than the pressure to which the tank is subjected while it is being filled by the oil delivery truck and driver.
We prefer this method for testing for evidence of leaks at buried oil tanks if there is a question of whether or not an oil tank has already leaked. The cost for soil testing is about the same as the first method where buried tanks are installed.
Multiple soil borings are collected around the tank, at a depth just past the level of the tank bottom. The soil samples are tested for petroleum product contamination.
This is considered the definitive test for oil tank leakage, and if the tank has not leaked, it provides more reliable documentation of that fact. More time is needed to complete the test as there is a delay for the lab work.
Consider that if you opted for the tank pressure test described earlier, and if the test showed that the tank has leaked oil into its surrounding soil, some additional testing is going to be needed to confirm the extent of soil contamination. It seems to me it's better to test the soil in the first place, thus also covering not only current but past conditions.
Finally, if we are told that an oil tank has been "remove" or "abandoned" at a property, we expect to be given the documentation that outlines who did what when, and importantly, what steps were taken to assure that there was no oil leak that was simply left for the next owner to discover and clean-up.
If adequate documentation is not provided, a soil test is certainly appropriate. One of my clients took this advice and discovered, and avoided having to pay for, a $60,000. site cleanup at the property he was buying.
See OIL TANK WATER CONTAMINATION for detailed advice on how to remove water from oil storage tanks. Excerpts are below.
Buried tanks, such as heating oil tanks, should be tested for amount of water present in tank bottom, and water should be pumped out. Even above-ground tanks can take on large amounts of water from roof spillage, condensation, or a bad oil delivery. (Photo at left).
In fact, water can accumulate in indoor or outdoor above ground oil storage tanks too, either from exposure to varying temperatures (in-tank condensation) or from the occasional delivery of bad oil which contains excessive water content.
A neat way to look for a history of water in the heating oil storage tank is to check the oil filter canister itself. Many oil burners are protected by a heating oil filter installed either at the tank or at the oil burner. (Every heating boiler burning oil should have one of these filters installed to protect the equipment.)
If the oil tank has a high level of water, especially if the oil lines run to the oil burner from the bottom of the oil tank, some of that water will have been making its way to the oil burner where, en route, it is (usually) trapped in the oil filter. If you open an oil filter container and see that its metal parts are rusted, or that there is a lot of rusty sludge in the bottom of the filter holding canister, the oil tank needs to be checked further for water
The oil service technician can check the level of water in an oil tank by putting some "oil finder paste" on the bottom of a stick or probe which is inserted into the tank and to its bottom. The paste changes color in the presence of water, showing, by the length of color change on the probe, the depth of water in the bottom of the tank. Obviously this trick is much easier if the tank is outside than indoors where a basement ceiling can make probing the oil tank difficult.
Ask your oil service company to perform this test.
Alternatively, if an underground oil storage tank also needs an oil tank tightness test or oil tank leak test, the Mesa 2-D TEST for OIL TANK LEAKS can also detect water leakage into the tank.
While we've found them lasting longer, a common life expectancy of buried oil tanks is 10-15 years. We do not have the same data for gas tanks. Life may be similar.
If the tank is to remain in use, ask your fuel supplier about using an additive or other methods to help remove water. Warning: on some older oil tanks which had a lot of sludge in the tank, as the de-watering additive (such as "4-in-1-HOT (TM)") was added to the tank we found an increase in the debris making its way to the heating oil filter. You should inspect the filter cartridge for water and debris and have it changed more frequently until this question is closed. It's more trouble but the end result is a more reliable oil storage tank and heating system.
See OIL TANK WATER CONTAMINATION for detailed advice on how to remove water from oil storage tanks.
Oil tank ultrasound screening program (photo above) is offered by some oil companies who scan the bottom section of above ground oil tanks to measure the thickness of the tank steel. Tanks that pass an ultrasound screening test may be insured against future leakage.
Typical oil tank thickness readings on an older above-ground indoor oil tank may range from 0.105 to 0.185 inches in thickness.
As a result we have seen tank test technicians "memorize" ten or 20 readings and then write them down by recollection of the "ballpark" figures. This is reasonable in that the technician is really just looking for any readings that cross the threshold of unacceptable tank steel thickness.
But it remains inaccurate and risks oil tank test data errors or skewing by operator error.
Further, if the test finds steel thickness readings close to the threshold of acceptability, we recommend that additional "spot checks" be taken of the tank's thickness in that area, rather than simply screening the tank bottom at larger spatial intervals.
See OIL TANK TREATMENTS for an oil treatment manufacturer's cautions about spot tests of oil tank thickness.
See WATER in OIL TANKS for added suggestions for finding and removing water from oil storage tanks.
What is the Most Reliable Approach to Evaluating an Oil Storage Tank for Risk of Near Term Leaks & Spills?
Watch out: critics argue that spot testing the oil tank bottom and lower sides for thin metal will not detect find all possible oil tank problems and may itself miss an existing pinhole oil leak. While I agree with that caveat there is more to be said.
Our tank photo at left shows an oil storage tank whose bottom area has been coated with an epoxy sealant in an attempt to cope with leaks. We already know the condition of this tank, without testing. It leaks.
U.S. & Canadian Standards groups and authorities pertaining to oil or other fuel storage tanks and tank testing include
A discussion of methods for finding evidence of previous or current buried tanks
at properties is
More detail about the causes of oil tank leaks, both buried and above ground tanks,
Home buyers should be sure to also review
Home owners who have old oil tanks above ground or any age oil tank below ground should also be sure to review
Continue reading at OIL TANK LIFE or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: vehicle tank or tank truck tank leak testing methodologies & research
Sirs: [Regarding your description of ultrasonic testing of oil storage tanks found at OIL TANK LEAK TEST METHODS]
We are an ISO/IEC 17020:2012 accredited inspection body and among our accredited activities is the inpection of tanks used for the transportation of dangerous goods, in accordance with the Unece ADR Agreement.
In order to conclude about the acceptability of the tank concerning its thickness, we must have a sampling plan including the places of measurements on the whole surface of the tank as well as the total number of measurements to be performed.
In your text above, you perform 12 measurements in the bottom of the oil tank and you give also the corresponding acceptability criteria.
So, I would strongly appreciate if you could inform me about an analogous statistical sampling plan as well as its reference, in order to perform my thickness measurements.
Thanks for your interesting note and question. I am not an expert on testing tanks of transport vehicles.
Our article discusses only stationary above ground heating oil storage tanks for which I do have some experience and for which I've done some research. What we've learned there might be of some help to you, but in my opinion the tanks on transport vehicles are subject to very different stresses and conditions so are likely to need a different sampling procedure than what we describe for home heating oil tanks.
The sampling plan used by the oil tank test technician was most likely never derived from statistical analysis but rather is based on decades of opinion and field observation about where leaks occur on heating oil storage tanks - particlularly along the bottom (water resides there in an oil tank thus rusts the steel) and also at the typical line along the tank side that would represent the average oil-water interface line (bacteria operating at that oil-water interface can increase corrosive action in the tank).
I think the leak testing approach for oil storage tanks would also be informed by the usual size of detectable leaks or leak-risk corroded spots on the tank (observed on cutting open of abandoned tanks or perhaps by other means) and thus would define the minumum spacing of the test points.
In other words, the number of samples must consider the total area that is at particular risk - something that will of course be different on larger tanks, tanks carrying different types of liquids and gases, tanks of different structures.
In my opinion, for transport vehicle type tanks, where mechanical stresses are involved, and where the tanks might be custom-assembled on or for particular vehicles, you must surely also want to check the condition of welds, joints, plumbing connections, and mounting points all subject to vibrational or other stresses, even vehicular collisions or other accidents.
Therefore also in my opinion, reliance only on a statistical sampling approach to choosing the type of vehicle tank test to be performed and the locus of the test sites, if it simply came up with a number of tank thickness tests, uninformed by tank type, uses, construction and mounting details, would be dangerous.
One might also want to look at some of the highest-risk applications of tank-like structures, such as underwater exploratory vehicles and submarines or space vehicles. Rakheja has published some interesting research that may particularly interest you.
Vehicle Tank or Transport Tank Truck Leak Testing & Standards Research
For other readers we identify the ISO/IEC standard to which you refer.
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