|
Objective:
The Department of Defense (DoD) owns more than 4,000 aboveground
storage tanks (AST) of varying capacities. Current federal
regulations deferred ASTs from the requirement to perform
monthly monitoring and/or annual precision testing because
no online leak detection system was available, but some states
require DoD facilities to remove their tanks from service
to install double bottoms and perform interstitial monitoring.
This project demonstrated the Low Range Differential Pressure
(LRDP) leak-detection system, which had previously been successfully
demonstrated on bulk underground storage tanks, on ASTs.
Technology
Description:
The
LRDP is an automatic, computer-controlled, mass-based measurement
system capable of detecting very small leaks in bulk fuel
ASTs. It relies on a closed reference tube that is the same
height as the tank and filled with fuel to the same level
as the fuel in the tank. If a leak occurs, a difference between
the height of the liquid inside the reference tube and the
bulk liquid develops, which is detected by a differential
pressure (DP) sensor. Because of the short dynamic range required
of the sensor, a dependable and robust, off-the-shelf DP transducer
can be used, while maintaining the precision required for
leak detection. The only difference in comparison to the underground
tank application for which the LRDP was earlier validated
is that a temperature sensor must be attached to the exterior
wall to compensate for diurnal expansion and contraction,
and tests should begin and end at night to minimize the effects
of these temperature variations.
Results:
The
system was first tested on a 54-foot-diameter, fixed-roof
tank to ensure that it could be used to perform accurate leak-detection
tests in a tank with a floating pan. A third-party evaluation
of the LRDP system, which was similar to and compliant with
the Environmental Protection Agency&8217;s standard test
procedure for bulk underground tanks, was then conducted over
a wide range of temperatures and induced leak conditions in
a 164.5-foot-diameter, 6,470,000-gallon bulk AST located at
the Fleet Industrial Service Center, Pearl Harbor, Hawaii.
Results showed that a single 20-hour test could detect a leak
of 0.932 gallons per hour with a 95 percent probability of
detection and 5 percent probability of false alarm. By averaging
multiple tests, the LRDP could detect leaks as small as 0.2
gallons per hour in a 108-foot-diameter tank with less than
5 percent probability of false alarm. Sensitivity improved
further with smaller diameter tanks.
Benefits
and Implications:
The
costs of installation and testing using the LRDP over a 10-year
period are 3-12 times less than conventional tracer methods
or other mass-based systems. Therefore, significant savings
can be realized across the DoD. Payback of the $50,000 capital
cost for the LRDP is 1-3 years. The technology also allows
facility operators to avoid out-of-compliance fines, the costs
of removing the tank from service for modifications (such
as installing a double bottom) or premature replacement, and
the cost of remediation for cleanup of undetected fuel spills.
The 24-hour LRDP test can meet the monthly monitoring requirements
for the full range of ASTs owned or operated by the DoD and
can be readily integrated into the DoD tank farm Fuel Automated
System. (Project Completed - 2004)
References:
1.
ESTCP Cost and Performance Report. May 2004. (PDF File
Format)
2. Major,
William R., Leslie A. Karr, George E. Warren, John A. Norbutas,
Frank Dellalibera and Kit L. Mack. United States Patent
Number: 6,148,854. System for Leak Detection from Underground
and Aboveground Fuel Storage Tanks. November 2000.
Principal
Investigator:
Ms. Leslie Karr
Naval Facilities Engineering Service Center
1100 23rd Avenue, Code ESC411
Port Hueneme, CA 93043-4370
Telephone: (805) 982-1618
Fax: (805) 982-4304
E-mail: leslie.karr@navy.mil
|
