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00726 CASED CROSSING TEST METHODS

Product Number: 51300-00726-SG
ISBN: 00726 2000 CP
Author: Dr. Thomas J. Barlo, Aida Lopez
Industry: Highways & Bridges
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Six methods to test electrical isolation of pipeline casings at highway and railroad crossings are critically analyzed; some are field tested. Three of the methods give more qualitative indications of the casing status, and three give more quantitative measures with data interpretation. The latter three methods, namely on and off pipe and casing potential, annulus resistance, and forced depolarization, may give accurate indications when the casing is electrically isolated or metallically shorted. However, none of the test methods reviewed appears to determine unambiguously the presence of an electrolytically shorted casing, except by deduction from the extremes of an isolated casing and a metallically shorted casing. Moreover, the methods can neither determine a metallically shorted casing with electrolyte present in the annulus nor assess the level of protection on the carrier pipe in the casing with an electrolyte present in the annulus. Despite the limitations of the methods, a low frequency of occurrence of corrosion with cased and/or shorted pipelines has been observed, due possibly in part to timely recognition and remediation of shorted casings. Key Words: buried pipeline, casings, test methods, corrosion
Six methods to test electrical isolation of pipeline casings at highway and railroad crossings are critically analyzed; some are field tested. Three of the methods give more qualitative indications of the casing status, and three give more quantitative measures with data interpretation. The latter three methods, namely on and off pipe and casing potential, annulus resistance, and forced depolarization, may give accurate indications when the casing is electrically isolated or metallically shorted. However, none of the test methods reviewed appears to determine unambiguously the presence of an electrolytically shorted casing, except by deduction from the extremes of an isolated casing and a metallically shorted casing. Moreover, the methods can neither determine a metallically shorted casing with electrolyte present in the annulus nor assess the level of protection on the carrier pipe in the casing with an electrolyte present in the annulus. Despite the limitations of the methods, a low frequency of occurrence of corrosion with cased and/or shorted pipelines has been observed, due possibly in part to timely recognition and remediation of shorted casings. Key Words: buried pipeline, casings, test methods, corrosion
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