Vista Research, Inc., has developed an innovative technology for the detection of small leaks in underground pipelines that are part of the aviation fueling systems found at commercial airports and military airfields. These include hydrant fuel distribution lines, which are typically 10 in. or more in diameter and up to several miles long, as well as the smaller fuel-farm pipelines associated with aboveground or bulk underground storage tanks that supply fuel to the hydrant lines. The fuel farm lines are typically 8 to 10 in. in diameter and are generally less than 1,000 ft long. On the hydrant lines, the new technology is implemented as a computer-controlled system called the Fully Automatic Line Tester, or FALT. On the underground lines associated with fuel-farm tanks, it is implemented as a system called the MAnual Line Tester (MALT). The MALTplus is a MALT that is equipped an electronic data acquisition system.
The MALT, MALTplus and FALT can be used as portable systems and transported from line to line for quarterly, semi-annual or annual tightness testing, or they can be permanently installed for periodic monitoring on a daily, weekly or monthly basis. A tightness test can be completed in approximately 2 h, and a test for monitoring purposes in approximately 1 h. They are attached to the line at a single location by means of a valve; any location along the line is suitable. No additional instrumentation or sensors have to be installed. These systems make a direct measurement, at the operating pressure of the line, of the rate of change in liquid volume that is due to a leak. The MALT, MALTplus and FALT achieve high performance because they compensate for thermal expansion and contraction of the product as part of the test protocol. To achieve a similar level of performance with conventional pressure or volumetric leak detection systems would require a pre-test waiting period of 24 to 48 h after the cessation of normal operations to allow the thermal changes to subside.
The FALT was demonstrated at the Miami International Airport, on a 1.86-mile-long underground hydrant line containing 45,750 gal of Jet-A fuel. Testing was conducted between midnight and 5:00 A.M. each day, after fueling operations had been terminated for the night. During each of two demonstration tests conducted, personnel simulated a leak in the line by withdrawing a small, measured volume of fuel. Agreement between the amount withdrawn and the rate of flow measured by the FALT was within 0.07 gal/h during the first test and within 0.31 gal/h during the second.
The MALT and the MALTplus were demonstrated at the Naval Air Station (NAS) North Island, Coronado, as part of the Naval Environmental Leadership Program (NELP). Over a three-day period, nine leak detection tests were conducted on a 650-ft, 8-in.-diameter underground line containing 1,700 gal of diesel marine fuel. During three of the tests, leaks of 0.08, 0.13, and 0.16 gal/h, respectively, were induced. Measurements of volume rate made by the MALT and MALTplus were in excellent agreement with the actual status of the line; for all nine tests, the one standard deviation uncertainty in the test results was 0.012 gal/h. The results of the demonstration indicated that the MALT and MALTplus could detect leaks as small as 0.1 gal/h accurately and reliably.