AE06.pdf

Results showed that two were leaking and that product

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results showed that two were leaking and that product was being lost at a rate of 85 L·s –1 (5.1 m 3 ·min –1 or 2.5 kt·yr –1 ). A 25 mm (1 in.) leaking valve was detected and fixed on the spot just by adjusting the stop. The largest leaker found to date was a 0.6 m (24 in.) valve leaking at a rate estimated at 63 L·s –1 (134 ft 3 ·min –1 ). Inservice Leak Detection for Aboveground Storage Tanks A proprietary technology has been developed for inservice testing and assessment of tank bottoms for aboveground storage tanks. The development started with the desire to locate leaks in tank floors, during which time it became apparent that badly corroded floors, even when not leaking, made a lot of noise. The details of how to use acoustic emission for evaluating tank integrity and floor condition are available in the literature. 10 The leak test is performed by instrumenting a tank with low frequency acoustic emission sensors. These sensors are designed to give the optimum performance when faced with high signal attenuation for large tanks and the possibility of background noise interference from environmental and mechanical noises. Sensors are coupled to the outside of the tank wall, evenly spaced and mounted near the shell-to-floor interface. Before testing commences, calibration is performed to ensure that the sensors are 221 Acoustic Leak Testing F IGURE 21. Flare gas valve. Arrows indicate points of interrogation for acoustic sensors.
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222 Acoustic Emission Testing F IGURE 22. Computer generated maps of acoustic data: (a) 24 m (79 ft) diameter diesel fuel storage tank; (b) 38 m (125 ft) diameter naphtha storage tank; (c) glass reinforced plastic liner for 67 m (220 ft) diameter crude oil tank. (a) (b) (c) X position Events Y position X position Events Y position X position Events Y position
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properly coupled and that the instrumentation is functioning satisfactorily. Because of low frequency sensor operation, the tank is allowed to still; pumps, agitators and valves are shut off; and piping attached to the tank is checked for possible extraneous noise sources. Weather permitting, data are collected in about 1 h. High winds, rain and hail generate considerable noise and are grounds for stopping or delaying the test. Tanks are generally filled with product to a prescribed level for this test. Under normal conditions, one to two large diameter tanks may be tested per work day. More can be tested if they are smaller and close together. Once data are collected, they are processed to determine where the noise sources originated. For determining the existence of a potential leak, the signature of the signal is examined and filtered to remove other possible noise sources. The filtered data are plotted on a location map to display potential leak locations. Sometimes, the process is rather straightforward, as shown in Fig. 22a.
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  • Fall '19
  • Acoustic Emission

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