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98566 AC CORROSION - A NEW CHALLENGE TO PIPELINE INTEGRITY

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Product Number: 51300-98566-SG
ISBN: 98566 1998 CP
Author: R.A. Gummow, R.G. Wakelin, SM. Segall
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Corrosion of steel by alternating current was investigated as far back as the early 1900’s. These early studies and others in the 1950-60’s indicated that AC corrosion of steel was only a fraction of an equivalent amount of direct current (i.e. less than 1% of a like amount of DC) and in addition was controlled to negligible levels when cathodic protection was applied to industry standards. In 1986 however, an investigation into a corrosion failure on a high pressure gas pipeline in Germany indicated that the sole cause of the failure was AC corrosion. This corrosion failure on an otherwise well protected pipeline resulted in the initiation of several laboratory and field studies which indicated, that above a certain minimum AC current density, normal levels of cathodic protection will not control AC corrosion to acceptable levels and that AC mitigation is often required to prevent serious corrosion. Several other AC corrosion sites were discovered at coating holidays during the follow-up investigations in Germany. A graph, relating AC voltage to holiday size at the minimum AC current density for corrosion, is presented to assist the pipeline operator in determining whether or not a pipeline is susceptible to AC corrosion activity. Keywords: AC corrosion, current density, corrosion rate, frequency, temperature, soil conditions, corrosion susceptibility, pipeline
Corrosion of steel by alternating current was investigated as far back as the early 1900’s. These early studies and others in the 1950-60’s indicated that AC corrosion of steel was only a fraction of an equivalent amount of direct current (i.e. less than 1% of a like amount of DC) and in addition was controlled to negligible levels when cathodic protection was applied to industry standards. In 1986 however, an investigation into a corrosion failure on a high pressure gas pipeline in Germany indicated that the sole cause of the failure was AC corrosion. This corrosion failure on an otherwise well protected pipeline resulted in the initiation of several laboratory and field studies which indicated, that above a certain minimum AC current density, normal levels of cathodic protection will not control AC corrosion to acceptable levels and that AC mitigation is often required to prevent serious corrosion. Several other AC corrosion sites were discovered at coating holidays during the follow-up investigations in Germany. A graph, relating AC voltage to holiday size at the minimum AC current density for corrosion, is presented to assist the pipeline operator in determining whether or not a pipeline is susceptible to AC corrosion activity. Keywords: AC corrosion, current density, corrosion rate, frequency, temperature, soil conditions, corrosion susceptibility, pipeline
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98565 AC CORROSION -CASE HISTORIES,TEST PROCEDURES,& MITIGATION

Product Number: 51300-98565-SG
ISBN: 98565 1998 CP
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Researches on AC Corrosion Risk Assessment Criteria for Cathodically Protected Carbon Steel

Product Number: 51317--8962-SG
ISBN: 8962 2017 CP
Author: Yanxia Du
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Experiments to study the effects of AC interference on cathodic protection (CP). Changes of CP potential and current density under AC interference and AC corrosion rates obtained. Effective CP potential under AC interference analyzed. Interference compared.
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The AC Close Interval Survey and Other Common AC Measurement Errors

Product Number: 51317--9455-SG
ISBN: 9455 2017 CP
Author: Wolfgang Fieltsch
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The measurement of induced AC voltages along a pipeline is a primary indicator of electrical safety hazards and AC corrosion risks under operating powerlines. This paper addresses several fallacies, misconceptions and common errors related to the measurement of these AC induced voltages.

 
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