L51656 Shielding Effects on Concrete and Foam External Pipeline Coatings

Protection of gas-transmission pipelines from external corrosion is achieved by the application of a good anticorrosion coating and cathodic protection. In very rocky areas, pipeline-construction operations sometimes dictate that an external impact-resistant or barrier material be applied over the pipe to protect the anticorrosion coating from damage during backfilling. The use of a select backfill, such as compacted sand, is often specified, but transportation of the backfill and access to sufficient right-of-way to truck the sand into more remote areas becomes costly. As an alternative, recent practice has been to specify that a barrier coating of concrete or urethane foam be applied over the anticorrosion coating. However, concern has been raised regarding possible shielding of cathodic-protection currents by these external barrier materials.

This project investigates the shielding effects of barrier coatings on attempts to maintain CP levels on natural gas pipelines. Investigation included lab experiments with five representative barrier coatings materials carried out to determine the degree to which shielding occurred and the levels of CP needed to overcome this effect when occurring.