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Evaluating the Effectiveness of Predicting Corrosion Rates of Buried Pipes and Tanks from Soil Resistivity Measurement at Nuclear Plants
Posted on June 17th, 2018

The Electric Power Research Institute (EPRI), "Interim Guidelines for Determining the Corrosion Rate for Use in Fitness for Service Evaluations of Buried Pipe, Report No. 3002003057," relies upon soil resistivity to evaluate the corrosivity of soils in proximity to buried pipelines.  Soil resistivity is most sensitive to soil particle size and mineralogy which controls the arrangement and abundance of soil pore water, and the type and abundance of ions in soil pore water solution.  Soil resistivity is used to predict outside diameter corrosion rates of buried pipes and tanks to project the system life of the structures. The RSCS and CorrTech technical team has been implementing soil corrosivity, in-situ corrosion rate and electrical potential monitoring assessments proximal to buried pipes at nuclear power facilities since 2013. Soil corrosivity assessments paired with co-located smart stack monitoring have been implemented at 5 geographically, and geologically unique sites, between 2013 and 2017, providing 45 assessment locations with sufficient data sets that include more than 450 analytical results and more than 225 individual Smart Stack readings.  The data sets collected by the RSCS and CorrTech team have been analyzed to determine if this EPRI guidance is effective.

The analysis and comparison of empirical corrosion rates with soil corrosivity results at nuclear power facilities do not agree with the EPRI guidance. There was no strong correlation between soil corrosivity parameters and co-located empirical corrosion rates in buried pipe environments at nuclear power facilities.  The analysis demonstrated that there is a correlation between total ion abundance and soil resistivity i.e. as total ion abundance increases soil resistivity decreases.  However, the study results did not show a correlation between total ion abundance or soil resistivity, which would be expected according to the EPRI guidance.  The overall results of the analysis suggest that the dense, mixed metal buried pipe networks at Nuclear power facilities, which are typically bonded to the site copper grounding grid, creates a unique environment where atypical parameters and processes are controlling outside diameter corrosion rates.  Further study is necessary to investigate galvanic corrosion processes, interference resulting from cathodic protection systems and enhanced corrosion rates as a result of elevated pipe/soil temperatures.

The full results of this study are to be presented by M.E. Darois and H.G. Kleinfelder at the 2018 American Nuclear Society Annual Meeting in Philadelphia PA and will be published in the meeting proceedings under the title “Analysis and Comparison of In-Situ Corrosion Rate Measurements with Co-Located Analytical Soil Corrosivity Parameters Along Buried Pipelines at Nuclear Power Facilities”. 

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