Above ground inspection methods such as Close Interval, AC Current Attenuation, Direct Voltage Gradient and Pearson surveys are often employed to examine pipelines for external corrosion, especially when in-line inspection and hydrotesting are not feasible. Compared to in-line inspection, these methods can be superior in identifying general areas of corrosion, however, they generally have a higher probability of missing significant defects. This paper examines the use of quantitative reliability-based methods for assessing the integrity of pipelines that have been inspected using above ground methods where these inspections are followed up by a selective excavation and defect sizing process. Special consideration is given to the inference of the size distribution of undetected defects when the number of detected defects is small.

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