Galvanic (Sacrificial) Anodes for Corrosion Prevention
What are Galvanic Anodes?
Galvanic anodes, also known as sacrificial anodes, are a key component of cathodic protection (CP) systems, preventing metal structures from corroding. These anodes work by utilizing their natural electrochemical potential to generate a protective current. As they corrode over time, they protect the structure by sacrificing themselves—hence the term sacrificial anodes.
The term sacrificial anode is often used interchangeably with galvanic anode, but technically, not all sacrificial anodes are galvanic. Impressed current anodes also degrade over time but require an external power source to function. In contrast, galvanic anodes generate their own protective current naturally. Despite this distinction, “sacrificial anode” is commonly accepted as a synonym for galvanic anodes in practice.
Unlike impressed current anodes, which require an external power source, galvanic anodes operate independently, making them a preferred choice for low-maintenance and long-lasting corrosion protection.
MATCOR offers a complete line of high-performance galvanic anodes for various applications, including:
- Underground pipelines and infrastructure
- Marine structures, including ships, docks, and offshore platforms
- Internal protection for tanks and process vessels
- Industrial applications in harsh environments
How do Galvanic Anodes Work?
Galvanic anodes operate on the principle of voltage differential, where the anode has a more electro-negative potential than the protected structure. This creates a natural flow of electrical current, preventing corrosion.
Compared to impressed current CP (ICCP) systems, which require an external power source, galvanic anodes provide a self-sustaining, maintenance-free solution for corrosion prevention.
Advantages of Galvanic Anodes
- Do not require an external power source
- Low maintenance and long service life
- Minimize stray current interference with other structures
- Simple installation with no ongoing power costs
Types of Galvanic Anodes
MATCOR provides galvanic anodes in various materials, shapes, and configurations to ensure optimal performance for different environments.
Magnesium Anodes (High and Standard Potential)
- Ideal for soil environments and freshwater applications
- High driving potential (-1.75V/CSE) for high-resistivity environments
- Often packaged with ion-rich backfill to enhance performance
Zinc Anodes
- Commonly used in brackish and seawater applications
- Highly efficient (90-95% utilization factor)
- Not suitable for high-temperature or high-resistance environments
Aluminum Anodes (Galvalum III and Other Alloys)
- Designed for offshore pipelines, ship hulls, and marine structures
Galvanic Anode Configurations
MATCOR’s galvanic anodes are available in various physical forms to suit different installation requirements:
- Bare metal anodes – Used in applications where direct metal-to-metal contact is required
- Packaged anodes in backfill – Ideal for underground installations, improving performance and longevity
- Anodes with external steel straps – Designed for easy mounting onto pipelines, ships, or other structures
- Ribbon anodes – Flexible configurations for protecting long or irregular surfaces
- Rod and special-shaped anodes – Custom solutions for specific applications
Selecting the right anode configuration ensures optimal current distribution, longevity, and performance based on the installation environment.
FAQ—Frequently Asked Questions about Galvanic Anodes
Yes, galvanic anodes are commonly called sacrificial anodes because they degrade over time while protecting the structure. The term sacrificial emphasizes how the anode corrodes (sacrifices itself) instead of the protected metal.
While galvanic anodes offer simplicity and reliability, they also have limitations:
* Lower driving force compared to impressed current systems
* Shorter service life in certain applications
* May not be suitable for some acidic environments
* Not ideal for high-resistance environments above 10k ohm-cm
* Difficult to adjust output once installed
Because galvanic anodes cannot be adjusted after installation, they require precise system design to ensure they provide just the right amount of protection for the intended lifespan.
Cathodic protection is an electro-chemical process that follows Ohms law (V=IR), where V (voltage) = I (current) x R (resistance).
In a galvanic anode system, the voltage difference between the anode and the protected structure is known as the driving potential. This difference determines how much current flows in the system, directly influencing the level of corrosion protection.
As galvanic anodes protect a structure, they undergo an oxidation reaction that transforms the metal anode into a metallic oxide. While metal itself is not destroyed, it gradually degrades and dissolves into the surrounding environment, reducing the anode’s mass over time.
The rate at which a galvanic anode is consumed in determined using Faraday’s Law, which quantifies the relationship between the number of metal atoms oxidized and the electrons transferred Consumption rates vary by anode type and are typically measured in kg/amp-yr (lbs/amp-yr).
Galvanic anodes are not 100% efficient—some of their mass is lost due to impurities, self-corrosion, or uneven degradation. The utilization factor, which varies by anode type, is essential when designing a CP system to ensure adequate lifespan and performance.
Magnesium anodes are available in two common alloys: high potential and standard.
* High potential magnesium anodes (-1.75V/CSE) are used in high-resistivity environments, such as fresh water and soil.
* Standard magnesium anodes(-1.55V/CSE) provide moderate protection and are more commonly used in lower-resistivity environments.
* Magnesium anodes typically have a lower efficiency (~50%), meaning they consume more quickly than other galvanic anodes.
Zinc anodes have a lower natural potential (-1.1V/CSE) than magnesium, making them best suited for low-resistance environments such as brackish and sea water applications.
* Zinc anodes are highly efficient (with a 90-95% utilization factor).
* They are not recommended for high-resistance or high-temperature environments.
In soil applications, zinc anodes are often packaged with gypsum-bentonite backfill to improve performance.
In the image below, steel galvanic anodes are used to protect the steel pipe piles for a jetty under construction.
Galvalum III is a high-performance alloy (alluminum/indium/zinc) used in marine environments.
* It has a higher potential than standard aluminum anodes (-1.1 to -1.15V/CSE).
* It is commonly used on offshore pipelines, ship hulls, and marine structures.
* Aluminum anodes have a utilization efficiency of 85-95%, making them highly effective in seawater applications..
Unlike impressed current systems, galvanic anodes do not have an external power supply for monitoring. This makes it difficult to monitor the anode system performance.
If monitoring is required, then it is common to have the anode connected to the structure through a test station equipped with a shunt. This arrangement provides access to measure the anode system’s current output without having to dig up the anode to structure connection.
For the most part, however, these galvanic systems are often installed with no significant monitoring provisions and are run until failure. This install-and-forget feature is simultaneously both an advantage and a disadvantage of galvanic anode systems.
Backfill materials help improve anode performance, especially in soil applications. The most common mixtures include:
* Magnesium anodes: 75% gypsum, 20% bentonite, 5% sodium sulfate
* Zinc anodes: a 50% gypsum, 50% bentonite
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Please contact MATCOR regarding your sacrificial anode requirements.
MATCOR’s mission is to solve your corrosion problems. In addition to our broad range of proprietary corrosion prevention products, we are ready to assist with your corrosion engineering and field service needs, including design, manufacturing, installation, commissioning and ongoing maintenance, as well as full turnkey solutions.
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