Abstract
Indirect survey techniques for underground pipelines are used to identify and define the severity of coating flaws, other anomalies and areas at which corrosion activity may have occurred or may be occurring. Of the several indirect inspection methods that are commonly used for External Corrosion Direct Assessment (ECDA), close-interval survey (CIS) is considered the most widely accepted and accurate method for determining the probability and severity of external corrosion threats to underground pipelines. For valid interpretation of the CIS inspection results, the pipeline operator must consider the specific conditions along the pipeline right-of-way and the expertise level of personnel analyzing the data. Typical criteria used to assess the severity of the indication include the actual measured potential at the base of the dip, the magnitude of potential change of the dip, the separation distance between ON and OFF potentials, and whether the ON and OFF potentials are above or below cathodic protection criteria. Depending on the experience of the individual analyzing the data, interpretation and classification of the CIS indications can often be inconsistent. This paper provides an analysis of CIS potential profile data based on practical experience using ECDA methodology under various pipeline conditions.
