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AC Corrosion At Other Frequencies Part A: Field Investigation And Mitigation

Picture for AC Corrosion At Other Frequencies Part A: Field Investigation And Mitigation
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Product Number: 51321-16807-SG
Author: Wolfgang Fieltsch, P. Eng.; Fation Shahinas, P. Eng.; Andreas Junker Olesen, Ph.D., Eng.; Lars Vendelbo Nielsen, Ph.D., Eng.
Publication Date: 2021
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$20.00
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A 2018 field investigation on an NPS 6, approximately 4 km long, liquid pipeline, identified a rectifier as
the likely source of the elevated DC and AC current densities, which resulted in AC corrosion anomalies
detected during in-line inspections (ILI). The findings of this case study, presented in the NACE Corrosion
2019 Paper No. 13188, indicated that the 120 Hz rectifier ripple may have contributed to the accelerated
AC corrosion at this location.
This follow-up paper is Part A of a two-part further investigation into corrosion rates on cathodically
protected structures due to AC frequencies other than the fundamental power frequencies of 50 Hz and
60 Hz. Part A involves additional field testing on the subject pipeline, and commissioning of the
recommended AC mitigation and monitoring systems. Part B of this investigation will be presented in a
separate paper (NACE Corrosion 2020 Paper No. 14916) and will discuss the results of laboratory testing
to determine corrosion rates of cathodically protected steel in simulated soil conditions at various AC
frequencies.

A 2018 field investigation on an NPS 6, approximately 4 km long, liquid pipeline, identified a rectifier as
the likely source of the elevated DC and AC current densities, which resulted in AC corrosion anomalies
detected during in-line inspections (ILI). The findings of this case study, presented in the NACE Corrosion
2019 Paper No. 13188, indicated that the 120 Hz rectifier ripple may have contributed to the accelerated
AC corrosion at this location.
This follow-up paper is Part A of a two-part further investigation into corrosion rates on cathodically
protected structures due to AC frequencies other than the fundamental power frequencies of 50 Hz and
60 Hz. Part A involves additional field testing on the subject pipeline, and commissioning of the
recommended AC mitigation and monitoring systems. Part B of this investigation will be presented in a
separate paper (NACE Corrosion 2020 Paper No. 14916) and will discuss the results of laboratory testing
to determine corrosion rates of cathodically protected steel in simulated soil conditions at various AC
frequencies.

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03698 Estimating AC Mitigation Requirements for Pipelines Installed in High Voltage AC Corridors: Fault Conditions

Product Number: 51300-03698-SG
ISBN: 03698 2003 CP
Author: R. D. Southey, Eng. W. Ruan, F. P. Dawalibi, S. Fortin
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51318-11231-Effects of Seasonal Variation on AC Interference and Mitigation Design

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This paper involved a case study of a project involving AC interference on pipelines located in Canada where soil resistivities increase rapidly by up to several orders of magnitude once water in the soil freezes in the winter.

 
Picture for Variances in Pipeline AC Interference Computational Modelling
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Variances in Pipeline AC Interference Computational Modelling

Product Number: 51319-12985-SG
Author: Gerald Haynes
Publication Date: 2019
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The AC interference between High Voltage AC (HVAC) power lines and pipelines has been modelled with various software programs all of which have a variety of input data which results in various results and outputs.Important aspects such as the soil resistivity along the pipeline route can have a significant impact on the pipelines coating resistance. This in turn affects both the computed AC voltages and current densities both of which can significantly affect personal safety and corrosion of the pipeline.Therefore the spacing between these field measurements along the pipeline route can have a significant effect on the pipeline integrity. Soil resistivity measurements collected every 1000ft versus every 5280ft (1 mile) can have a dire consequence on the corrosion results and the matter is exacerbated where these soil resistivity measurement values change significantly along the route. The accuracy of the soil resistivity field data relative to the actual routing (wetlands rivers low and high resistivity’s etc.) will also affect the correct placement of the AC Mitigation (grounding) as well as the resistance of the grounding which in turn has a cost implication to the asset owners and/or operators.Other aspects such as the power line LEF/EMF may also be used to “calibrate” the AC Interference especially where load data is absent.This paper addresses the critical importance of collecting adequate data for the AC Interference studies to prevent costly installations and to mitigate the incorrect positioning of AC Mitigation systems due to inadequate information.
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