External corrosion risk assessment (ECRA) has been conducted on steel pipelines that have been buried in high consequence areas for more than thirty years. The ECRA program included the following four steps: 1) Risk Identification, 2) Cathodic Protection (CP) History survey, 3) Alternating Current Voltage Gradient (ACVG) survey and 4) In-line Inspection (ILI) using Magnetic Flux Leakage (MFL) tools. As a result of risk identification, the corrosion risk was roughly divided into two categories: 1) corrosion at coating holidays, 2) corrosion due to electrical shielding. Evaluations of the pipe surface at more than a hundred of excavation sites based on ACVG survey have ensured the successful elimination of the corrosion risk at coating holidays. Thus continuous CP maintenance was proven to be extremely effective to eliminate severe corrosion risks including DC stray current corrosion and AC corrosion. Scheduled in-line inspection using MFL tools will be conducted to assess the other corrosion risks such as corrosion under disbonded coatings. ECRA proactively seeks to prevent the size of external corrosion anomalies from growing to the extent that it will threaten structural integrity.

Subject
Holidays, Rail, Pipe surfaces, Pipe to soil potential, Pipelines, Coating surveys, Metallic structures, Current densities, AC voltage gradient, Alternating current corrosion, Risk management, Construction, External corrosion
Keywords:
External corrosion, Pipeline, Cathodic protection, Alternating current voltage gradient survey, Coatings, Coating holiday
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2005
Association for Materials Protection and Performance (AMPP)
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