Abstract
The results of this work quantify the validity of external corrosion direct assessment (ECDA) as an integrity verification tool with respect to external corrosion. The ability of ECDA to detect pipeline coating flaws and corrosion damage was statistically verified by performing ECDA on approximately 20 miles of pipe and conducting 66 excavations. Out of the 66 excavations, 43 were ECDA indications (i.e., predicted to have a coating flaw and/or corrosion) and 23 were controls (i.e., predicted to have pipe and coating in good condition). Comparison of the median area of exposed metal at coating flaws, disbonded coating, and metal damage areas showed that the populations of indications and controls were different at a 95% confidence interval. This result demonstrates that the ECDA process, as performed by the NGA member companies, discriminated between pipeline locations with respect to coating and corrosion damage. The results of binary logistic regression showed that, for the pipelines in the project, the probability of finding a coating flaw or corrosion damage (of any size) at an ECDA indication was 98%, and the odds of finding a coating flaw or corrosion damage at an indication as compared to a control was approximately 300 to 1. Continuous logistic regression showed that larger coating flaws were more likely to be detected (i.e., the probability of detecting a coating flaw increased with area of exposed metal). Although the occurrence of mechanical damage (i.e., 3rd party damage) was not sufficient to allow statistical analysis, it is noteworthy that mechanical damage was found at three indications). Identification of mechanical damage in the project was consistent with the premise that it can be found when associated with coating damage.
