The interpretation of indirect inspection data and selection of direct examination locations are crucial steps in conducting a successful external corrosion direct assessment (ECDA) process. This paper presents advances in the interpretation of indirect inspection data and selection of ECDA direct examination locations and how the accurate selection of locations most susceptible to external corrosion would improve pipeline integrity. Comprehensive case studies from several ECDA digs, practical experience and lessons learnt from these case studies are fully presented.

Failures in oil and gas pipelines due to leaks have led regulators to require operators to implement ever more rigorous inspections. ANSI(1)/NACE(2) SP0502– Pipeline External Corrosion Direct Assessment Methodology has been developed to ensure the safe operation of pipelines and prevention of external corrosion in non-piggable pipelines, as well as piggable pipelines, where it can be used as a supplement to ILI. This standard requires a minimum of two indirect inspections to confirm the locations on a pipeline most susceptible to external corrosion.

The direct examination step of ECDA involves prioritizing the findings of indirect inspections and excavation (for underground pipelines) of locations where coating flaws and corrosion are most likely, the measurement of coating damage and corrosion defects, evaluation of damage severity, and root cause analysis.

The precise selection of direct examination locations would ensure that pipeline operators can reduce unnecessary and costly excavations while making sure locations most susceptible to external corrosion are addressed to prevent future wall loss due to corrosion.

Subject
Indirect inspection, External corrosion direct assessment, Cathodic protection, Cathodic potential, Pipeline integrity management, Pipelines, Coating damage, AC voltage gradient, Anomalies, Corrosion data, External corrosion, Instant off potential, Types of corrosion
Keywords:
ECDA digs, External Corrosion Direct Assessment, DC voltage gradient, AC voltage gradient, AC current attenuation, close interval survey, cathodic protection, coating anomaly, data interpretation, severity classification
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2017
Association for Materials Protection and Performance (AMPP)
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