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' TEST METHOD ' Operations were conducted from a test van which has been designed specifically for leak detection applications by Pelagos' engineers. All AE ' sensors, interface electronic and control-analysis software mounted inside the van and used for the tanktestingwere designed, fabricated and installed by Pelagos Corporation. 1 i Leak locations were determined by measurement of the arrival times of leak ' transient signals at sensors placed in an array on the exterior wall of the storage tank. Improved sensitivity over older AE systems has been realized by ' the use of high-speed analog'-to-digital (A/D) converters. The high-speed converters allow the acoustic signals, after analog amplification and ' filtering, to be digitized and input into a computer system, where rigorous statistical analysis is performed by proprietary software. The process t measures amplitudes of continuous-noiae (ambient) background and of all transient events (i.e., those caused by leaks) to better than one-percent accuracy full scale. The high resolution of the measurement techniques means ' that leak events with signal strengths of only a few percent above background noise levels can be detected'. All raw test data were recorded on an instrument-grade analog tape recorder. The archived (taped) AE data allow subsequent off-site analysis a 7 d further study be necessary. ' The testing of each tank was performed using six AE sensors. Four sensors were attached at equally spaced intervals around the perimeter near the base of the tank and two approximately eight feet above the bottom sensors. All sensors were coupled to the outside tank wall with a silicone lubricant after a small surface area had been cleaned of paint and rust. Sensor-mounting procedures followed closely the guidelines in ASTM designation E650-85. ' Sensors were held in place magnetically. Sensor identifications for each tank are specified in Table 2. 1 ' -4-