Reference Information
Key information from reference documents and guides (e.g.) or succinct descriptions of concepts (e.g. what is risk and how do I visualize it)
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Research & Technical Content
Key takeaways, results from ongoing research tasks, and how they are applied.
1 - Research Result Summaries
Latest results from ongoing tasks
Corrosion Failure of a Conductor Located Near an Industrial Site
A utility reached out to EPRI corrosion team to discuss a conductor failure that occurred near an ammonium nitrate plant. It is suspected that the conductor failure was due to corrosion. The line is located about 45 yards from the plant cooling towers.
A conductor sample taken near the failure point was sent to EPRI for condition assessment.
AAAC Flint Forensic Report
All aluminum conductor performance is not well understood in coastal and desert climates. This report provides an overview of the environmental conditions at a series of spans where a AAAC failed, identifies the type of corrosion and the cause of the failure. From this we may better understand the time to failure for a conductor in-service with similar environmental conditions.
Geometry Factor Development
Research has shown that the outer strand layers on a conductor provide some environmental protection to the steel strands. Conversely when the strand layers are opened in a “birdcage” the corrosion is accelerated on the steel strands. Both conditions have been quantified for many types of conductors and may be applied to an atmospheric corrosion rates as a correction factor. This allows engineers and asset managers to model the time to failure for conductors in their service territory.
Condition Assessment Comparison of Two Coastal Aluminum Conductors
Research into all aluminum conductor corrosion has revealed a very interesting mode of failure that is dependent upon specific environmental conditions. This report contains health assessments for two all aluminum conductors in similar environments with the 50 year old conductor in “as new” condition and the 20 year old conductor failing due to exfoliation and hydrogen embrittlement.
Corrosion Monitoring System (CMS) The Corrosion Monitoring System (CMS) has migrated from a research tool into a standalone data collection system to help us understand corrosion anomalies and monitor “at risk” structures. The CMS has its own power supply, data collection, cellular connection and a host of atmospheric and subgrade sensors to identify changes in both the environment and the degradation rate of the asset. That data may be used to model conductor degradation, ground grid degradation or any asset in atmospheric or soil exposure. Perhaps the greatest benefit of deploying the CMS is understanding severe types of corrosion such as stray current or circulating current corrosion.
Laboratory Corrosion Resistance Evaluation of Conductor Strands A utility service territory can cover a vast area, resulting in transmission lines being exposed to a wide range of corrosive environments including coastal and industrial sites. A question often asked by members is “Which conductors should I use in the most corrosive areas of my service territory?”. Although this question could be answered using field sampling of conductors and conductor inspection technologies, EPRI is currently working on measuring the corrosion resistance of individual conductor strands in a laboratory setting.
1.1 - Corrosion Monitoring System
Originally designed as a research tool but has now found a home in monitoring “at risk” structures and anomalies that remain unexplained. The Corrosion Monitoring System (CMS) is a self-contained system that has power management, power supply, data storage, cellular connectivity and may be expanded to collect both atmospheric and subgrade data (see Figure 1).
Figure 1: The Corrosion Monitoring System installed at the Charlotte Campus in the underground test facility
The objectives of deploying the CMS is threefold, the first is to understand why assets degrade but also discriminate between corrosion types, the second is to locate suspect areas containing “at risk” assets and the third is to provide environmental data to support degradation models. Models consist of the following data and may be easily charted to trend both corrosion rates but also changes in subgrade and atmospheric weather (see Figure 2). The corrosion rates may be gathered for steel, zinc and copper for subgrade models or steel, zinc, aluminum, and copper in atmospheric models (see Figure 3).
Figure 2: The Corrosion Monitoring System Dataset for Atmospheric and Subgrade Monitoring
Figure 3: Algorithm for Substation Ground Grid Corrosion Monitoring and Installation Methods
EPRI has developed extensive atmospheric and soil corrosivity maps that may be augmented using data from the CMS data sets. Many departments within the utility may then use this new information for more accurate and informed life cycle decisions (see Figure 4).
Figure 4: Atmospheric and Soil Corrosivity Maps with Severity Categories for Corrosion
The CMS data sampling rate may be set for a very high- or low-resolution dependent upon the application and how often the anomaly or environment changes. Figure 5 illustrates a Corrosion Monitoring System collecting subgrade data to determine if a cathodic protection system is performing properly and meeting the acceptance criteria of -850 mV or 100 mV shift.
Figure 5: Monitoring a Cathodic Protection System using a CMS
Reviewing the chart, we may see that all of the bonded coupons are polarized more negative than -850 mV which is the acceptance criteria recommended by AMPP (formerly known as NACE). This polarization level allows the stake owners to determine that their asset is well protected and may provide many years of service.
2 - Reference Information
Key information from reference documents and guides (e.g.) or succinct descriptions of concepts (e.g. what is risk and how do I visualize it)
3 - Videos
Updates on tasks or tests
Forensic Analysis of Hardware due to Corrosion Damage Forensic analysis of in-service or failed hardware allows an understanding of what caused the damage. Often there are clues that uncover the type of stresses that led to performance loss such as electrical, mechanical, thermal or chemical stresses. Once the type of stress is understood, a mitigation method may be prescribed in the form of material substitution, coating system application, cathodic protection or even an inhibitor. When there are multiple stresses in combination it may require multiple mitigation methods but those must then be aligned with the environment.
3.1 - Forensic Analysis of Hardware due to Corrosion Damage
Forensic analysis of in-service or failed hardware allows an understanding of what caused the damage. Often there are clues that uncover the type of stresses that led to performance loss such as electrical, mechanical, thermal or chemical stresses. Once the type of stress is understood, a mitigation method may be prescribed in the form of material substitution, coating system application, cathodic protection or even an inhibitor. When there are multiple stresses in combination it may require multiple mitigation methods but those must then be aligned with the environment.