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• Applications Note 1 1 <br /> STORAGE TANK LEAK DETECTION <br /> Problem Description <br /> Many above-grade storage tans now in service were constructed 20 or <br /> more years ago - sufficient time for the mechanisms of metal corrosion and <br /> stress-fatigue cracking to weaken and perhaps breach the tank floors. The <br /> resultant tank floor leaks are often unnoticed by plant personnel during <br /> . tie performance of their daily routines. These leaks can be costly, both <br /> interms of product loss and potential liability for environmental <br /> pollution. <br /> Until recently, techniques for tank-floor integrity testing were <br /> generally limited to visual i Lapection or still gauging. Visual <br /> inspections require the tank to be emptied, cleaned and carefully examined, <br /> putting the tank out of service f r weeks or more. Even then, some small <br /> leaks can be overlooked. <br /> Still-gauging methods are adequate for only the largest leaks. The <br /> accuracy of most tank-installed liquid level gauges is usually one-eighth <br /> inch at best. A proauct loss reflected by a 0.062-inch level drop for a ' <br /> 100-foot diameter tank translates to a 306 gal/day leak. If this 1/16-inch <br /> drop in product level is not discernible from the masking effects of fluid <br /> expansion, losses in excess of 2650 barrels annually will go undetected. <br /> At twenty dollars per barrel, th s loss amounts to over $53,000 for a <br /> single tank. The associated liability risks of ground-water contamination <br /> could involve much greater potential costs. <br /> Acoustic-emission (AE) technology offers an economical solution to `, <br /> leak detection in these large-volume above-grade storage tanks as well as <br /> in pipelines, heat exchangers, valves and pressure vessels. <br /> P-Ma(�c}F� <br /> 'Cb�tl�V'a 9173 Chesapeake Drive <br /> !� Son Diego, California 92123 <br /> Telaphone:t619) 292-8922 0 Telex 295468PLGS UR <br />