Does Corrosion Impact the Performance of Copper-Clad Steel Wire?

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Oct 08, 2024, 11:11 ET

BRENTWOOD, Tenn., Oct. 8, 2024 /PRNewswire/ -- Copperweld^® Copper-Clad Steel (CCS) conductors are known for their steel core, which provides enhanced strength. However, one question often arises: How can steel, a metal prone to rust, resist corrosion when buried underground for years?

CCS conductors are metallurgically bonded, combining the best properties of copper and steel. When manufactured using the correct processes and high-quality materials, CCS can surpass the service life of solid copper, even in cases where the steel core is exposed during installation.

Compared to solid copper, CCS offers superior break-load strength, greater endurance, and remarkable resistance to corrosion. In fact, CCS conductors often outlast solid copper wire, even when exposed to the elements. CCS conductors have maintained a century-long reputation for durability.

CCS's added strength and resilience have helped engineers optimize power grids for decades. Still, some engineers seek reassurance that CCS is safe for buried applications.

In this article, we'll address some of the most common corrosion-related questions about CCS.

Common Corrosion Concerns

1. What happens if the copper corrodes and exposes CCS's steel core?

CCS conductors are designed so that the copper layer makes up most of the exposed surface area. This design puts the copper where it counts—on the outer surface, in contact with soil, air, and connectors. Copper, with its high conductivity and superior corrosion resistance, acts as a shield for the steel core.

While copper does oxidize and turn green over time, this patina actually enhances corrosion resistance, extending the lifespan of CCS. Special soil conditions, such as those containing cinder fill, can accelerate copper corrosion, but these cases are exceptions. In most environments, copper corrodes at an extremely slow rate.^{1, 2}

According to "A Technical Report on the Service Life of Ground Rod Electrodes," copper corrodes at a rate of only 0.000005 inches per year in typical soil. At that rate, it would take 2,200 years to corrode through the 0.011-inch copper cladding on a Copperweld Century 19 No. 9 conductor!³

2. What if the steel is exposed due to impact or scraping? Will corrosion cause premature failure?

Even when steel is exposed, CCS can endure corrosion. In many installations, connectors such as exothermic or swage joints fully encase the cut ends of a conductor, protecting the exposed steel. However, when the steel is exposed, it forms a protective rust "scab," which seals the steel from further corrosion.

In worst-case scenarios, corrosion advances only a small distance—usually 2-3 times the diameter of the wire—before the rust scab halts further damage. Even when isolated corrosion occurs, the surrounding copper surface remains intact, maintaining conductivity or signal across the length of the conductor. This is the same protective behavior observed in Copper-Clad Steel ground rods and tracer wire over decades of use. Of course, all conductors, including CCS and solid copper, should be handled with care to avoid damage during installation.²

Lab and Field Testing

In the Lab
Copperweld conducted extensive testing from 2004 to 2009 to assess the effects of indentation and nicking on CCS conductors. The goal was to study the effects of exposed steel in underground applications. After five years of burial in various soil conditions, the results were promising:

Indented: Only 1 out of 50 samples that were indented to expose steel showed minimal corrosion after five years. The damage did not significantly affect the conductor's performance. Notably, the force used to indent CCS far exceeded what would be required to sever solid copper wire.
Scraped: In severely scraped/nicked samples, where the steel core was exposed, oxidation occurred and only proliferated at an expected rate. The conductor's electrical and mechanical properties remained stable.⁴

In the Field
In 2011, after 49 years of service in a Kentucky substation, Century 7 No. 5 CCS conductors were unearthed. The conductors showed no corrosion beyond typical copper oxidation, and the copper cladding still met ASTM standards.

At the ends of the wires, corrosion formed a steel 'scab'. The copper layer remained intact, and there was no visible corrosion between the copper and steel interface.⁵

Long-Term Studies

The National Bureau of Standards conducted a comprehensive underground corrosion study spanning over 45 years. This research, covering 37,000 specimens in 95 soil types, concluded that CCS conductors with 10-13 mils of copper cladding have an expected service life of 40 to 50 years. However, this estimate is conservative—Copperweld CCS products often exceed these standards.²

Why Choose CCS Over Solid Copper?

While copper is often seen as the gold standard for grounding, Copper Clad Steel offers several advantages that make it a better choice for many applications:

Superior Strength: CCS conductors offer 2-3x the break-load strength of solid copper. This makes them ideal for power grid and utility applications where tensile strength is critical to preventing mechanical failure.
Extended Service Life: With five times the flex-fatigue endurance of solid copper, CCS conductors are more resistant to bending, jerking, and vibration—making them perfect for applications that experience frequent mechanical stress.
Secure Connections: CCS's annealed steel core and copper exterior allow for stronger, longer-lasting connections that remain stable for decades, even under harsh conditions.
Reduced Theft: Copper theft is a significant issue, especially as copper prices rise. CCS wires, with their lower street value, are less attractive to thieves, offering additional protection for utility installations.

Not All CCS Conductors Are Created Equal

It's important to note that not all CCS conductors meet the same standards. Inferior products from foreign competitors may fail prematurely due to cracks and gaps in the copper layer, which allow moisture to corrode the steel core. These products lack the metallurgical bond that defines Copperweld's CCS.⁶

Copperweld's proprietary bonding process ensures a seamless bond between the copper and steel, preventing moisture from penetrating the conductor and leading to galvanic corrosion. This is why Copperweld CCS consistently outperforms other CCS conductors and delivers reliable service for over 50 years.

How to Verify Genuine Copperweld^® Products

To ensure you're using a high-quality CCS conductor, look for the Copperweld^® branding on the reel wrap and label. Genuine Copperweld conductors provide the durability, strength, and corrosion resistance that have made them a trusted choice for over a century.

Read the full article here, or to learn more about Copperweld Power Grid products, visit copperweld.com/power-grid.

Sources:

Long-Range Field Burial Study Probes Underground Corrosion
Corrosion Properties of Copperweld Wire and Strand
A Technical Report on the Service Life of Ground Rod Electrodes
The Effects of Corrosion on Tracer Wire with a Copper-Clad Steel Center Conductor
Corrosion on Buried Copper Clad Steel
Copperweld Metallurgical Laboratory Report #547

Copperweld is the world leader in bimetallic wire and cable specializing in power, grounding, and signal conductors for building construction, power grid, utilities, communications, and transportation. For over 100 years, their mission has been to make the most reliable, sustainable, and innovative wire and cable products on the market. Copperweld's metallurgical expertise and engineered solutions result in bimetallic products that enhance performance, extend service life, conserve copper, improve energy efficiency, and reduce theft incentives. Their American-made products are manufactured in the USA, and the culture of excellence and innovation that inspired them over a century ago still drives them today.

SOURCE Copperweld