LRDP
Leak Detection and Integrity Monitoring for Bulk Underground Storage Tanks
The Vista LRDP (Low-Range Differential-Pressure) system is a mass-based leak detection and monitoring system for bulk fuel tanks, including USTs (underground storage tanks) and ASTs (aboveground storage tanks). It quantitatively measures the rate of any leak that might be present, giving the results in gallons per hour.
The LRDP was initially developed for the world's largest USTs, which are owned and operated by the U.S. Navy [2]. The Red Hill tanks, buried over 100 feet deep in the hills above Honolulu, are 100 feet in diameter and 250 feet high, and each contains 12.5 million gallons of fuel. The LRDP has also been used for testing some of the bulk USTs owned by the Department of Defense (DoD) [1]. The LRDP has been integrated into the DoD Fuels Automated System (FAS), making it compatible with all the DoD's bulk fuel storage facilities.
The LRDP consists of three integrated components:
an in-tank sensor unit for making measurements
a local controller to implement a test and analyze the data from the test
a host computer to initiate a test and to report and archive the results of the test
The LRDP can, with only minor hardware and software modifications, also conduct leak detection tests on ASTs.
How the LRDP Works
The key component of the LRDP is the vertical "reference" tube, which spans the full usable height of the tank (see diagram). The fuel in the tank is allowed to enter or leave the reference tube through a valve located at the bottom of the tube. When the tank is to be tested, the valve is closed, isolating the fuel in the tube from the fuel in the rest of the tank.
The level of fuel in the reference tube mimics that in the tank in every way except for the level changes due to a leak. A differential-pressure sensor, which is housed in a sealed container at the bottom of the tube (which is itself at the bottom of the tank) then detects very small changes in pressure between the fuel in the tank and the fuel in the tube, with the LRDP converting pressure changes to the equivalent level changes. Thus, when the valve is closed, the differential-pressure sensor directly senses, and the LRDP quantifies, the level changes due to a leak (if a leak is present).
The LRDP achieves a very high level of performance against small leaks because of (1) its high precision and (2) its inherent method of compensating for the thermal expansion and contraction of the fuel in the tank. In addition, the LRDP compensates for evaporation and condensation within the tank.
The LRDP not only delivers high performance but is rugged and fieldworthy.
Most importantly, because of its unique, patented design, the LRDP eliminates the two factors responsible for the poor performance of other mass-based measurement systems—thermal drift of the pressure sensors and thermally induced vertical movement of the in-tank sensor unit. All of the sensors are mounted in a sealed container at the bottom of the tank, where temperature changes are too small to affect sensor performance; and the in-tank sensor is held in place by a bellows-type mounting system that prevents changes in tank geometry from affecting the position of the sensor.
The LRDP was developed by Vista Research with technical support from the U.S. Naval Facilities Engineering Service Center (NFESC) and funding from the Pollution Abatement Ashore Program managed by the Naval Facilities Engineering Command and sponsored by the Environmental Protection, Safety and Occupational Health Division (N45) of the Chief of Naval Operations. The LRDP was demonstrated and validated under the Department of Defense's Environmental Security Technology Certification Program (ESTCP).
