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51317--9722-The Use of Ultrasound for Monitoring the Impact of Induced AC Corrosion on Underground Structures

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An alternative method for directly measuring effectiveness of AC-induced corrosion control and mitigation efforts. This method takes the form of traditional coupons imbedded with ultrasound testing (UT) transducers designed to directly measure and track coupon metal loss and related corrosion-induced anomalies.

Product Number: 51317--9722-SG
ISBN: 9722 2017 CP
Author: Rob Leary
Publication Date: 2017
Industry: Energy Generation
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The Use of Ultrasound for Monitoring the Impact of Induced AC Corrosion on Underground StructuresIt is generally accepted that Alternating Current (AC) corrosion on cathodically-protected underground structures is the result of the combined action of induced AC voltage local cathodic protection conditions chemical and physical conditions of the soil. Indeed NACE standards and guidelines exist related to AC voltages and current density thresholds that are established to protect both personnel and underground structures such as pipelines. As a result the industry is developing an understanding of how to best mitigate and monitor such risks. One of the most widely accepted monitoring methods is tracking the current density rather than just AC voltages through the use of coupon test stations installed adjacent to the structures requiring protection. Coupons are typically installed to measure and monitor induced AC potentials and current densities that are compared to levels known to produce corrosive effects. Such data are combined with other pipeline design/installation parameters and high voltage AC performance parameters in order to yield information for mitigating and preventing AC corrosion. The industry has depended on the use of these analytical and indirect methods and tools for measuring the effectiveness of mitigation efforts. However there is a need for better methods to measure mitigation efforts and determine when corrosive conditions exist. This paper presents an alternative method for directly measuring the effectiveness of induced AC corrosion control and mitigation efforts. This method takes the form of traditional coupons imbedded with ultrasound testing (UT) transducers designed to directly measure and track coupon metal loss and related corrosion-induced anomalies. Rather than managing some of the challenges of electrical resistance or electrical-chemical measurement techniques ultrasound is used to directly measure coupon thickness on any required schedule – manually or remotely. The UT-based coupons are integrated into traditional cathodic protection test stations the results of which are combined with traditional AC and DC current density measurements for more accurate and repeatable tracking of the mechanical integrity of underground structures as well as cathodic protection system performance. Early testing results and the performance of field installations are presented.

Key words: Alternating current, cathodic protection, corrosion, ultrasound, coupons

The Use of Ultrasound for Monitoring the Impact of Induced AC Corrosion on Underground StructuresIt is generally accepted that Alternating Current (AC) corrosion on cathodically-protected underground structures is the result of the combined action of induced AC voltage local cathodic protection conditions chemical and physical conditions of the soil. Indeed NACE standards and guidelines exist related to AC voltages and current density thresholds that are established to protect both personnel and underground structures such as pipelines. As a result the industry is developing an understanding of how to best mitigate and monitor such risks. One of the most widely accepted monitoring methods is tracking the current density rather than just AC voltages through the use of coupon test stations installed adjacent to the structures requiring protection. Coupons are typically installed to measure and monitor induced AC potentials and current densities that are compared to levels known to produce corrosive effects. Such data are combined with other pipeline design/installation parameters and high voltage AC performance parameters in order to yield information for mitigating and preventing AC corrosion. The industry has depended on the use of these analytical and indirect methods and tools for measuring the effectiveness of mitigation efforts. However there is a need for better methods to measure mitigation efforts and determine when corrosive conditions exist. This paper presents an alternative method for directly measuring the effectiveness of induced AC corrosion control and mitigation efforts. This method takes the form of traditional coupons imbedded with ultrasound testing (UT) transducers designed to directly measure and track coupon metal loss and related corrosion-induced anomalies. Rather than managing some of the challenges of electrical resistance or electrical-chemical measurement techniques ultrasound is used to directly measure coupon thickness on any required schedule – manually or remotely. The UT-based coupons are integrated into traditional cathodic protection test stations the results of which are combined with traditional AC and DC current density measurements for more accurate and repeatable tracking of the mechanical integrity of underground structures as well as cathodic protection system performance. Early testing results and the performance of field installations are presented.

Key words: Alternating current, cathodic protection, corrosion, ultrasound, coupons

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