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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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.