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Excavation, Removal And Evaluation Of Coupons Exposed To AC Interference While Connected To An Operating Product Transmission Pipeline

Picture for Excavation, Removal And Evaluation Of Coupons Exposed To AC Interference While Connected To An Operating Product Transmission Pipeline
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Product Number: 51321-16566-SG
Author: Philip Simon, P.E / John McCaffery
Publication Date: 2021
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This paper presents the results of an investigation that included the excavation and analysis of six (6) coupons test stations exposed to changing levels of induced AC interference from adjacent HVAC transmission lines. The coupon test stations were installed on a liquid product pipeline. The locations were selected based on AC interference historical records and accessibility. The coupon excavation and removal procedures were performed in a manner that allowed the soil near the coupons to be observed intact and separated from the surrounding backfill. The coupon conditions were photographed and documented upon excavation, prior to cleaning and after all deposits and corrosion products were removed. The maximum pit depth, diameter reduction and morphology all were documented and compared to the AC interference history (A/m2 levels and time of exposure). Notable findings include that all the examined CP coupons showed some AC assisted corrosion damage. In some cases, this damage was severe even with a high level of cathodic protection. The field testing and laboratory analysis showed that the CP current collecting on the bonded coupon caused significant changes in the chemistry in the adjacent soil compared to the nearby backfill.

Key words: liquid product pipeline, induced AC interference, soil chemistry, AC assisted corrosion damage

This paper presents the results of an investigation that included the excavation and analysis of six (6) coupons test stations exposed to changing levels of induced AC interference from adjacent HVAC transmission lines. The coupon test stations were installed on a liquid product pipeline. The locations were selected based on AC interference historical records and accessibility. The coupon excavation and removal procedures were performed in a manner that allowed the soil near the coupons to be observed intact and separated from the surrounding backfill. The coupon conditions were photographed and documented upon excavation, prior to cleaning and after all deposits and corrosion products were removed. The maximum pit depth, diameter reduction and morphology all were documented and compared to the AC interference history (A/m2 levels and time of exposure). Notable findings include that all the examined CP coupons showed some AC assisted corrosion damage. In some cases, this damage was severe even with a high level of cathodic protection. The field testing and laboratory analysis showed that the CP current collecting on the bonded coupon caused significant changes in the chemistry in the adjacent soil compared to the nearby backfill.

Key words: liquid product pipeline, induced AC interference, soil chemistry, AC assisted corrosion damage

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