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10115 A New Thermodynamic Criterion and a New Field Methodology to Verify the Probability of AC Corrosion in Buried Pipelines

Picture for 10115 A New Thermodynamic Criterion and New Field Methodology to Verify Probability of AC Corrosion
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Product Number: 51300-10115-SG
ISBN: 10115 2010 CP
Author: Panossian, Filho, Almeida, Silva, Laurino, Oliver, Albertini
Publication Date: 2010
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One of the current and important challenges faced by cathodic protection professionals is to access the corrosion probability of cathodically protected buried pipes subject to alternating current (AC) interference (i.e., AC corrosion). In practice, it is very common for cathodically protected pipes to be buried adjacent high voltage AC electrical power lines and electric energy distribution systems. These electric power systems can produce stray AC current in soil or induced AC current in the pipe. This AC current can cause severe corrosion on buried pipes which are supposed to be catholically protected. There are several criteria cited by the literature to evaluate the probability of AC corrosion; however, they are inefficient since failures due to AC corrosion have been reported on pipelines which displayed electric and electrochemical parameters within the acceptable limits of those criteria. This work has as an objective to propose a new thermodynamic criterion and presents all the necessary equipment for obtaining in the field the necessary electric and electrochemical parameters to apply the proposed criterion in a safe way. Those parameters are obtained from the waveform of pipe-soil interface AC+DC off potential. Two devices were developed: a probe composed of a modified permanent Cu/CuSO4 reference electrode coupled with corrosion coupons and an electronic alternating switch device. Some measurements conducted on existing pipelines are also presented.

Keywords: cathodic protection, AC current, AC corrosion
One of the current and important challenges faced by cathodic protection professionals is to access the corrosion probability of cathodically protected buried pipes subject to alternating current (AC) interference (i.e., AC corrosion). In practice, it is very common for cathodically protected pipes to be buried adjacent high voltage AC electrical power lines and electric energy distribution systems. These electric power systems can produce stray AC current in soil or induced AC current in the pipe. This AC current can cause severe corrosion on buried pipes which are supposed to be catholically protected. There are several criteria cited by the literature to evaluate the probability of AC corrosion; however, they are inefficient since failures due to AC corrosion have been reported on pipelines which displayed electric and electrochemical parameters within the acceptable limits of those criteria. This work has as an objective to propose a new thermodynamic criterion and presents all the necessary equipment for obtaining in the field the necessary electric and electrochemical parameters to apply the proposed criterion in a safe way. Those parameters are obtained from the waveform of pipe-soil interface AC+DC off potential. Two devices were developed: a probe composed of a modified permanent Cu/CuSO4 reference electrode coupled with corrosion coupons and an electronic alternating switch device. Some measurements conducted on existing pipelines are also presented.

Keywords: cathodic protection, AC current, AC corrosion
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