News
Con Edison Media Relations
Richard D. Mulieri, Director
Telephone: (212) 460-4111
For Immediate Release: September 3, 1997
NEW DEVICE HELPS ENSURE LEAK-FREE
OPERATION OF LARGE FUEL TANKS
As part of Con Edison's program to achieve
environmental excellence, company engineers, working with
ASTTest Services Inc. of Melbourne, Florida, have developed
a device capable of detecting oil leaks as small as one-half
gallon per hour from a one million gallon tank. The device
is designed to test tanks to ensure leak-free operation and
can be used prior to or following internal inspections to
detect leaks.
A United States patent was granted to ASTTest Services
Inc. for the leak-detection system on April 17, 1997. Con
Edison will share the patent royalties.
"The standpipe leak-detection system shows great
promise for testing large underground and above-ground oil
tanks," said Vincent dePass, Con Edison's senior
environmental engineer. "The test doesn't require the tank
to be drained and can be completed in 48 hours after a short
setup time. It's a winner for the environment and a
practical tool," he added.
The fuel oils and kerosene that are used by Con Edison
in its power plants to generate electricity and steam, are
sometimes stored in above-ground and
underground tanks.
Regulatory Requirements and Testing Difficulties
New York state code requires that all large underground
and above-ground tanks with access via a hatch or manway be
internally inspected every 10 years. An ASTTest Services
tank-bottom study determined that routine internal
inspections may not detect very small holes in tanks. This
can mean that after incurring expensive tank draining, oil
sludge removal, cleaning and integrity testing of the tank
bottom, a very small leak may still go undetected.
Internal tank inspections also require the tank to be
out of service for extended periods of time and unavailable
to supply oil to company power plants. In addition, if
internal inspections miss a small hole, a tank could be
returned to service with a small leak that could contaminate
the environment.
A New Testing Device Is Developed
Engineers from the company's Environment, Health and
Safety, and Research and Development departments worked with
ASTTest Services to develop a new leak- detection system
using an open bottom vertical tube, or standpipe. While the
tank is full of oil, the standpipe assembly is inserted. It
contains a level sensor and several oil temperature
detectors, or thermistors, inside the pipe's entire length.
Other thermistors measure the temperature on the outside
skin of the tank. The system works by developing a
correlation between the downward pressure of oil called the
pressure head, temperature and level in the standpipe as
compared to the bulk oil in the tank, taking into account
thermal expansion and contraction. A nearby van equipped
with electronic equipment periodically polls and records
data from the detectors.
A portable weather station monitors barometric
pressure, ground-level temperature, dew point and wind
direction and speed during the test. These measurements
make it possible to correct for any abnormal test results
due to weather.
Tests Are Successful
A test of the system was conducted on a one million gallon
oil tank at the company's Arthur Kill power plant over a 116-
hour period with an indicated leak of 0.25 gallons per hour.
The test met the objective of detecting a leak of less than
0.5 gallons per hour, which can occur through a hole of 0.5
millimeters or 0.02 inches in diameter, the size of a pencil-
point.
Future Approved Use
In December 1995 the American Petroleum Institute (API)
amended Standard 653 Tank Inspection, Repair, Alteration and
Reconstruction to include a statement approving the use of
leak detection tests for periodic assessment between
internal inspections.
New York State Department of Environmental Conservation
officials have agreed that testing with the Con
Edison/ASTTest device of in-service large underground and
above-ground tanks would provide an immediate environmental
benefit with early detection of suspected leaks. The device
can be used to test these tanks prior to or after
internal inspection in order to identify leakage.
Con Edison is one of the nation's largest investor-
owned utilities, with nearly $7 billion in annual revenues
and $14 billion in assets. The company provides electric,
gas and steam service to three million customers in New York
City and Westchester County, New York.
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