Corrosion Defect Management Based on a Quantitative Growth Approach

Enbridge Pipelines Inc. operates one of the longest and most complex pipeline systems in the world. As such, thorough, system-wide understanding of defect behavior is a critical aspect of Enbridge’s Integrity Management Program (IMP). To enhance understanding of corrosion behavior, and aid in determination of in-line inspection revalidation intervals, a quantitative corrosion defect assessment approach has been developed and implemented for the Enbridge system. To date nine trap-to-trap pipeline sections have been completed using this approach. Utilizing defect data from consecutive high-resolution corrosion in-line inspection tool runs in correlation with pipe attribute information and environmental characteristics, a statistical approach has been developed to determine the distribution of the corrosion growth rates along these nine sections of pipeline. Validation was achieved through comparison with other corrosion growth rate assessment methods. This comparison was also used to develop refinements to the approach. The approach provided an upper-bound estimate of corrosion growth and was considered appropriate for system-wide application where other defect-by-defect comparison methods can be time, labour, and cost intensive. Use of this upper-bound estimate of corrosion growth in combination with field metrics, operational history of the pipeline, defect trending and, where available, additional sources of corrosion growth rate determination have provided the operator with an effective, practical, and defensible tool set for determining subsequent in-line inspection reassessment intervals across the pipeline system. Data integration inherent in the process has also provided valuable insight regarding corrosion growth rate drivers as affected by pipeline and environmental factors. While focusing on trap-to-trap sections of the Enbridge system that have been inspected with multiple high-resolution in-line inspection tools, this paper/presentation will also discuss a statistical corrosion growth rate approach for trap-to-trap sections with only one high-resolution in-line inspection run.