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ECDA Techniques for Shorted and Non-shorted Cased Crossings
With outside force damage and third-party damage shielded by the casing wall, the leading cause of failures of cased pipe segments is external corrosion. Where inline inspection or pressure testing is inapplicable or impractical, external corrosion direct assessment (ECDA) methodology may be used. Due to shielding of the casing wall, the indirect inspection tools traditionally used for ECDA of uncased pipes had not been considered to be applicable to cased segments until Table 2 on tool selection for ECDA in the NACE ECDA Standard RP 0502-2002 was clarified (now SP0502-2010 version).
To apply ECDA methodology to cased pipe segments, not all indirect inspection tools traditionally applicable to uncased pipe segments are applicable. The most challenging casings for ECDA are the ones that lack test facilities. For those casings, wireless tools such as Pipeline Current Mapper (PCM) and PCM with A-Frame (A-Frame) have been used in the industry for casing ECDA. Although these tools have been in field use for several years, their performance for cased segments is not well understood. When the test facilities are present, the Close Interval Survey (CIS) with or without current interruptions is often used. The three tools mentioned above can be used to detect if a casing and the carrier pipe have metal-to-metal contact or a short, or if they are isolated (casing annulus clear), or if there is electrolyte in the casing annulus (electrolytic coupling). Since the severity of external corrosion of cased segments is dependent on the contact status between a casing and the carrier pipe, it is important to detect the contact status. The result of the detection can help to distinguish if an immediate (shorted casing) or a scheduled (electrolytically coupled casing) or a monitoring (clear casing) action needs to be taken in order to manage the integrity of the cased segments.
The objective of this project is to validate the effectiveness of PCM, A-Frame and CIS in detecting the contact status between a casing and the carrier pipe. Since the detection of the contact status is made based on the criteria set for each of the tools, the effectiveness of each tool depends on the tool criteria. When possible, the criteria of the tools will be evaluated and modified to improve the tool effectiveness.