For more than half a century, cased crossings have been used to support oil and gas steel pipes for crossing highways, railways, or rivers. Leaks or ruptures of cased crossings have occurred that resulted in casualties and property damage. Unlike uncased pipes buried in soils, which can be assessed for external corrosion directly and indirectly, the presence of a steel casing wall makes it challenging, even if possible, to conduct these assessments. The effect of the casing wall on the external corrosion of the carrier pipe inside the annulus is not well understood; it is unclear what tools can be used to effectively inspect the cased pipes. Empirical experience from the pipeline industry has shown that a few tools can be used to detect the contact status between a casing and the carrier pipe, which can help assess the severity of the carrier pipe external corrosion. Unfortunately, the criteria used to detect a contact status vary by user for the same tool and thus, the effectiveness of these criteria is uncertain. This paper reports results from a recent study aimed at evaluating the effectiveness of AC current attenuation, AC voltage gradient, and close interval (potential) survey as tools for detecting the contact status between a casing and the carrier pipe.
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