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51315-5780-Cathodic Shielding Effects of In-Trench Pipeline Supports

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Product Number: 51315-5780-SG
ISBN: 5780 2015 CP
Author: Daniel Fingas
Publication Date: 2015
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When installing pipelines in rocky areas additional mechanical safeguards may be necessary to protect the coating. These safeguards may take the form of intermittent supports which elevate the pipeline off the trench bottom. As such supports are non-metallic and are installed directly against the pipeline coating the pipeline at the location of the supports may be shielded from cathodic protection current.The cathodic shielding effects of two such supports a structured pipeline pillow and a standard spray-in polyurethane foam support are investigated and compared. Coating defects were simulated with coupons installed under both supports on the surface of a fusion bonded epoxy coated NPS24 pipe section with an additional coupon installed to act as a control. The pipe coupons and supports were immersed in a tap water electrolyte until stable corrosion potentials were reached. Cathodic protection supplied by a magnesium anode was applied until the system reached a steady-state. The resistance between each coupon and the anode was measured at the start and end of the experiment. At suitable intervals the cathodic protection current for each coupon was measured independently and the cathodic protection current density was calculated. In addition coupon instant-off potentials were measured in order to characterize the polarization of each coupon. The current density and potential results are compared to one another to assess the relative cathodic shielding effects.Keywords: Cathodic Shielding Foam In-Trench Pipeline Supports Shielding.
When installing pipelines in rocky areas additional mechanical safeguards may be necessary to protect the coating. These safeguards may take the form of intermittent supports which elevate the pipeline off the trench bottom. As such supports are non-metallic and are installed directly against the pipeline coating the pipeline at the location of the supports may be shielded from cathodic protection current.The cathodic shielding effects of two such supports a structured pipeline pillow and a standard spray-in polyurethane foam support are investigated and compared. Coating defects were simulated with coupons installed under both supports on the surface of a fusion bonded epoxy coated NPS24 pipe section with an additional coupon installed to act as a control. The pipe coupons and supports were immersed in a tap water electrolyte until stable corrosion potentials were reached. Cathodic protection supplied by a magnesium anode was applied until the system reached a steady-state. The resistance between each coupon and the anode was measured at the start and end of the experiment. At suitable intervals the cathodic protection current for each coupon was measured independently and the cathodic protection current density was calculated. In addition coupon instant-off potentials were measured in order to characterize the polarization of each coupon. The current density and potential results are compared to one another to assess the relative cathodic shielding effects.Keywords: Cathodic Shielding Foam In-Trench Pipeline Supports Shielding.
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Two different types of foams, open cell (low density) and closed cell (high density), were used. The testing was conducted on two FBE-coated pipelines buried in a trench with various foaming system combinations applied as breakers.

 
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Impact of Foam Trench Breakers and Ditch Pads on Pipeline Cathodic Protection

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The testing covers the impacts of various commercial Structural polyurethane foam materials on cathodic protection current distribution on coated pipelines based on laboratory testing of key performance parameters.
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06043 DETERMINING THE CP SHIELDING BEHAVIOR OF PIPELINE COATINGS IN THE LABORATORY

Product Number: 51300-06043-SG
ISBN: 06043 2006 CP
Author: G.R. Ruschau, Y.Chen
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The tendency of pipeline girth weld coatings to shield cathodic protection (CP) current was studied in the laboratory. Epoxy, epoxypolyurethane, polyurethane, and wax were investigated.  Results showed that the liquid coatings, when applied extra thin to accelerate the kinetics of absorption and current transmission, all disbonded by blistering, and all allowed CP current to be transmitted.
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