Galvanic corrosion, also known as bimetallic corrosion, is a destructive process that occurs when different metals or alloys are placed in electrical contact within an electrolyte, which leads to the degradation of one metal - the anode. This document provides a galvanic corrosion chart that outlines the compatibility of various metals and alloys.
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It also offers guidance on the appropriate selection of fasteners to mitigate the risk of galvanic corrosion. Understanding these elements is crucial in the design and maintenance of machinery, structures, and other systems where different types of metals and alloys are used concurrently.
What is Galvanic Corrosion?
Galvanic corrosion occurs naturally when two metals that have distinct electrochemical characteristics are in direct contact, facilitated by the presence of an electrolyte. This convergence initiates a chemical response, that leads to to an accelerated corrosion rate of one metal (known as the anode), while the corrosion of the other metal (referred to as the cathode) is decelerated or remains stable.
The degree of corrosion, or galvanic action, is determined by the difference in potential between the two metals on the galvanic series. This process is a significant consideration in the design and maintenance of systems where different types of metals are combined, especially in environments with high moisture or salinity, such as marine or industrial settings.
Understanding galvanic corrosion is important to protect and maintain the longevity of metal structures and components. By being aware of this phenomenon, we can take practical steps to prevent or minimize its effects and ensure the durability of our materials.
Importance of a Galvanic Corrosion Chart
A Galvanic Corrosion Chart is a vital tool for preventing corrosive damage in metal assemblies. It ranks metals and alloys based on their potential for corrosion when exposed to different metals in an electrolyte environment. This chart helps categorize metals from most prone to corrosion (anodic) to most resistant (cathodic), to aid in decision-making and preventing corrosion.
By using the chart, contractors and homeowners can determine metal compatibility and predict galvanic corrosion likelihood and severity. It is invaluable in industries like marine, construction, and machinery, where careful metal selection and pairing can significantly extend equipment and structure lifespan, and reduce maintenance and replacement costs.
The above ratings (High, Medium, Low) represent a generalized corrosion potential based on the difference in electrode potentials of the metals. In actual environments, the corrosion risk can be influenced by other factors like the presence of salts, moisture, and the relative areas of the anode and cathode. Wherever possible, it is advisable to use fasteners and base metals that are close together in the galvanic series, and/or to isolate the metals with suitable coatings or insulators to prevent direct contact.
Please note that the corrosion potential ratings are general indications and actual performance may vary based on environmental conditions, coatings, and other factors.
Guidelines for Fastener Selection Based on Galvanic Action
When selecting fasteners, a fundamental understanding of the principles of galvanic action is crucial. Here are a few guidelines to follow:
Consider Material Compatibility
Refer to the Galvanic Corrosion Chart when pairing fasteners with base metals. Try to match metals that are close together on the series to minimize potential differences and reduce the risk of galvanic corrosion.
Avoid High-Risk Pairings
As per the chart, some pairings, such as aluminum with steel fasteners or galvanized steel with copper fasteners have a high risk of corrosion. Avoid such combinations whenever possible.
Use Insulating Materials
If a high-risk pairing is unavoidable, consider using insulating materials (like rubber or plastic washers) between the base metal and the fastener. This can help prevent direct metallic contact and hence the galvanic action.
Choose Coated Fasteners
Opt for fasteners coated with a protective layer of non-reactive metal. This can help decrease the risk of corrosion. However, be aware that any scratches or damage to the coating could expose the underlying metal and initiate corrosion.
Employ Regular Maintenance
Regular inspection and maintenance are essential, especially in high-moisture or salinity environments. Check for early signs of corrosion and replace affected parts promptly to prevent further damage.
It’s important to remember that these guidelines are general recommendations. The actual corrosion risk might vary depending on environmental conditions and other specific factors in your project. Always consult with a corrosion specialist when in doubt.
Fastener Systems: Ensuring Durable and Corrosion-Free Connections
To ensure the security of your metal-to-metal connections, choose Fastener Systems Inc. for all your fastener needs. We offer guidance in selecting compatible materials and can also provide coated fasteners for added protection.
Contact our team today to learn more about our products and how we can help you with your specific needs!
