Challenges in the application of DCVG-survey to predict coating defect size on pipelines

Abstract

Corrosion is often the cause of pipeline failure potentially resulting in disasters causing damage and fatalities. To maintain the integrity of non-piggable lines, NACE’s External Corrosion Direct Assessment (ECDA) methodology is commonly applied to assess external corrosion that can occur at coating defects on underground pipelines. Work presented here is from a validation exercise carried out on the results of ECDA assessment using subsequent excavation data. The ECDA was carried out over 300 kilometres of crude oil pipelines with excavation carried out at 200 locations. This paper models the relationships between pipeline coating defect area (area with coating breakdown) , corrosion depth, Direct Current Voltage Gradient (DCVG) measurements (in terms of %IR values), and factors capturing diverse environmental conditions through novel application of regression models. This paper sheds light on the challenges in drawing conclusions in the assessment of corrosion from Direct Current Voltage Gradient (DCVG) inspection data and other types of data that form key inputs to ECDA. We expect that the analyses shown here using innovative regression models will support more reliable predictions of external corrosion in pipelines.