Tank Tightness Testing

TANK TIGHTNESS TESTING, "precision testing", or "volumetric testing"

This test must be combined with either manual tank gauging or inventory control. Used primarily on tanks of less than 15,000 gallons capacity containing gasoline and diesel fuel.

OPERATION

Most tightness tests are "volumetric" methods in which change in product level or volume in a tank is measured very precisely over several hours. Consequently, product temperature may also have to be measured very precisely since changes in temperature can affect product volume.

For most methods, a net decrease in volume over the time of the test indicates a leak.

Testing equipment is temporarily installed in the tank, usually through the fill pipe. The tank must be taken out of service during the test. Testing normally takes from 6 to 12 hours. Many test methods require the product in the tank be at a certain level before testing. This may require the addition of product. Most methods require the services of a testing company.

VARIATIONS

Some methods require all measurements and calculations be made by hand. Other methods are highly automated. After the tester sets up the equipment, a computer controls the measurements and analyses the results.

There are several acceptable ways of measuring product temperature including mixing the product so that it is a uniform temperature, using a sensor that calculates average temperature from measurements made throughout the product depth, and using at least 3 temperature sensors at different product levels to calculate an average value.

Some methods measure product properties that are temperature independent, such as mass, to avoid temperature measurements.

REQUIREMENTS

A test must be able to detect a leak as small as 0.1 gallon/hr. Tightness tests must be performed periodically as follows:

TANK TYPEMINIMUM FREQUENCY
newevery 5 years for 10 years following installation
existing, upgradedevery 5 years for 10 years following installation
existing, not upgradedevery year until 1998

After the time periods given above, you must have a monitoring system that can be performed at least once a month.

COST

Testing companies charge from $250 to $1000 for a simple tank tightness test. Many factors may increase this cost, including:

Reduce costs by testing several tanks and by doing any necessary repairs/preparations before the testing crew arrives.

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