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Methodology to Estimate Edge Effect on Direct Current Cathodic Protection Coupons

Picture for Methodology to Estimate Edge Effect on Direct Current Cathodic Protection Coupons
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A model was developed to study the effects on the CP coupon current density and interpretation of the CP coupon data for a given holiday. The model results indicate that the most dominant factor affecting coupon is the size, followed by corrosion potential.

Product Number: 51317--8976-SG
ISBN: 8976 2017 CP
Author: Pavan Shukla
Publication Date: 2017
Industry: Corrosion Monitoring and Control
$0.00
$20.00
$20.00

Direct Current (DC) Cathodic Protection (CP) coupons are widely used in the pipeline industry to monitor CP potential and estimate current densities at the holidays. Various DC coupon shapes include flat metal surface embedded in an insulating plane long and small rods and stubby cylinders. Of these flat coupons including rectangular and disk shapes are most widely used as they are assumed to be representative of the holidays at the pipe surface. However flat coupons embedded in insulating plane are prone to current density measurement errors due to edge effect. The current density at the coupon’s edges is expected to be several times higher than the center of the coupon. Because the holidays on pipeline are surrounded by coated surfaces the current density distribution at the coupons is expected to be different than the holidays. Specifically a holiday surrounded by the coating will have lesser degree of edge effect due to coating thickness compared to the coupon surface. This paper investigates edge effect on the CP coupon current density and identified a methodology to interpret the coupon current data at the holiday surface.

Keywords: coating holidays, cathodic protection, test coupons

Direct Current (DC) Cathodic Protection (CP) coupons are widely used in the pipeline industry to monitor CP potential and estimate current densities at the holidays. Various DC coupon shapes include flat metal surface embedded in an insulating plane long and small rods and stubby cylinders. Of these flat coupons including rectangular and disk shapes are most widely used as they are assumed to be representative of the holidays at the pipe surface. However flat coupons embedded in insulating plane are prone to current density measurement errors due to edge effect. The current density at the coupon’s edges is expected to be several times higher than the center of the coupon. Because the holidays on pipeline are surrounded by coated surfaces the current density distribution at the coupons is expected to be different than the holidays. Specifically a holiday surrounded by the coating will have lesser degree of edge effect due to coating thickness compared to the coupon surface. This paper investigates edge effect on the CP coupon current density and identified a methodology to interpret the coupon current data at the holiday surface.

Keywords: coating holidays, cathodic protection, test coupons

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