Corrosion of Buried Steel at New and In-Service Infrastructure (2023) / Chapter Skim
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7 Standard and Evolving Monitoring Practices
7 Standard and Evolving Monitoring Practices
Pages 77-92
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From page 77... ...
potential surveys, are also commonly employed. There are no regulations related to monitoring buried steel in the geo-civil or water pipeline industries.
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From page 78... ...
The table and text are ordered based on methodologies that primarily use extracted steel samples from the field for laboratory measurements (e.g., direct metal loss measurements, sample corrosion potential, LPR, PDP, and EIS) , and then those that are primarily used in the field (potential surveys and ILI)
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From page 79... ...
average rate over time of exposure; need multiple coupons to get trend. Linear polarization Nondestructive Mostly laboratory Measuring applied current during Determine Rare in geo- Need Tafel slopes to get corrosion resistance (LPR)
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From page 80... ...
CSE are more robust than the others and are commonly used for field measurements of the corrosion potentials of buried structures. When reporting potentials, it is essential to include the type of reference electrode used in the measurement.
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From page 81... ...
In the oil and gas pipeline industry, coupons provide grounding pathways that can interfere with CP systems. Box 7.2 provides an example of the use of inspection elements by the California Department of Transportation.
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From page 82... ...
Polarization of the specimen to potentials far from Ecorr can damage the specimen, so the method is considered to be destructive and is not used for monitoring in the field. Linear Polarization Resistance and Tafel Slope Measurements The LPR technique is primarily7 a laboratory-based method used to estimate theofcorrosion Corrosion Buried Steelrate of and at New extracted In-Service Infrastructure coupons and in-service steel elements.
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From page 83... ...
Potential Surveys to Locate Defects In many corrosion studies, the measurement of the corrosion potential refers to the potential drop at the electrode interface measured relative to a reference electrode (see Box 7.1)
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From page 84... ...
The side-drain measurements are examined for magnitude and polarity changes to determine the anodic locations. Alternative potential survey methods in the pipeline industries include alternating current voltage gradient (ACVG)
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FIGURE 7.5 Schematic of a cell-to-cell survey where the copper–copper sulfate electrode is placed over the pipeline's centerline.
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FIGURE 7.7 Schematic of a side-drain survey where one copper–copper sulfate electrode is positioned above the center of the pipe and the other one is positioned parallel to the pipe at approximately 5–10 feet offset.
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From page 87... ...
Surveys are conducted along the length of the steel infrastructure and measure changes in the way current flows over the surface of buried steel. Those test points are connected to a rectifier and ground bed containing anodes for the CP system.
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From page 88... ...
88 CORROSION OF BURIED STEEL AT NEW AND IN-SERVICE INFRASTRUCTURE FIGURE 7.9 Visual depictions of rectifiers, anode ground beds, and test points for a cathodic protection system on an oil and gas pipeline. Rectifiers are often tapped from a high-voltage power distribution system and connected to the anode ground bed and the pipeline.
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From page 89... ...
This technology is mainly used for tighter, planar- or crack-like defects rather than volumetric defects such as a corrosion defect. FIGURE 7.11 Schematic of close interval potential surveys.
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From page 90... ...
In the water pipeline industry, a number of different ILI or direct inspection methods are used, including remote-field electromagnetic scans, broadband electromagnetic probes, remote-field transformer coupled scans, MFL scans, in-pipe acoustic velocity wall thickness, and ultrasonic techniques. These also can be performed by a human or remotely using a smart pig.
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From page 91... ...
It may be possible to use this method to identify corrosion of buried steel; however, as Hubbard et al.
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From page 92... ...
. As these methods have proven successful in the laboratory for monitoring corrosion and in the field for monitoring strain of buried steel and buried reinforced concrete infrastructure, they are an aspirational method for monitoring corrosion of buried infrastructure.
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