ABSTRACT
Structural polyurethane foam (SPF) materials are being used to provide physical support (“ditch pads”) and erosion control (“trench breakers”) with pipeline installations. These SPF materials are either sprayed with the pipeline in place or pre-sprayed into a cured shape to support a pipeline. As an organic material that comes into contact with a coated-steel pipeline, concerns have been raised about the potential, if any, for a SPF to create “electrical shielding” and limit or prohibit cathodic protection current from reaching a coating holiday or defect in a coated steel pipeline.
The paper summarizes the results of research sponsored by the Pipeline Research Council International concerning the subject of shielding. The testing covers the impacts of various commercial SPF materials on cathodic protection current distribution on coated pipelines based on laboratory testing of key performance parameters.
INTRODUCTION
The subject program addresses concerns of cathodic protection “shielding.” Cathodic protection is required to control corrosion of a steel pipeline at coating defects exposing the underlying metal. Cathodic protection shielding may be defined as a design or natural feature that limits or prohibits cathodic protection current from reaching specific areas of a pipe surface requiring current for corrosion control. Many features that may limit cathodic protection current must be accounted for in a proper design. This program specifically examines the use or application of structural polyurethane foams (SPF) in contact with a coated underground pipeline and the impact of the SPF on cathodic protection current. Concerns exist for corrosion control at holidays in the pipeline coating if significant shielding occurs. (1), (2), (3) SPF products enter into the shielding question when used to physically support pipeline installations or retard water erosion. As an alternative to traditional sandbags, industry developed “foam ditch pads” (FDP) fabricated from SPF. The SPF offers high levels of stability, substantial load-carrying ability, and comparatively simple installation. The FDP can be pre-cast or cast on-site. The pipeline will typically be lowered and rest on the FDP. This results in direct foam-to-pipeline contact; the foam would not be bonded to the pipeline.
