Preventing Galvanic Corrosion: Factors And Methods

Galvanic corrosion is driven by the difference in electrochemical potential between the two metals, which leads to corrosion of the more reactive metal. It is important to know how to prevent this type of corrosion to protect metal structures and prolong their lifespan.

In this article, we will discuss effective strategies to shield your metal components from galvanic corrosion, helping them stay strong and resilient for many years.

What Is Galvanic Corrosion?

Galvanic corrosion occurs when two distinct metals are electrically connected in the presence of a conductive fluid. In this interaction, one metal acts as the anode and loses electrons through oxidation, while the other serves as the cathode, where reduction takes place and remains protected from corrosion.  

Essential Conditions For Galvanic Corrosion

• Presence of Two Different Metals: At least two dissimilar metals are required.
• Electrical Contact: The metals must be in direct electrical contact with each other.
• Electrolyte: An electrolyte, such as water or moisture, is necessary to facilitate the process.

Influencing Factors For Galvanic Corrosion

Potential Difference

A larger difference in electrochemical potential between two metals results in a higher corrosion rate for the anode. When a more reactive metal is paired with a less reactive one, the more reactive metal will corrode at a faster rate.

Fatores ambientais

Factors like temperature and pH can accelerate or slow down corrosion. Higher temperatures often increase reaction rates, while extreme pH levels can either promote or inhibit corrosion depending on the metals involved.

Surface Area Ratio

The size of the metal surfaces matters. Specifically, when the anode has a relatively smaller surface area compared to the cathode, it tends to deteriorate more quickly. This is because the smaller area concentrates the electrochemical reactions, leading to quicker deterioration.

How To Prevent Galvanic Corrosion？

Seleção de materiais

To minimize the risk of galvanic corrosion, it’s important to select metals with similar electrochemical potentials. For example, stainless steel and aluminum can have a large potential difference, making them a poor choice together. Selecting metals from the same family or with compatible properties can help prevent corrosion.

Protective Coatings and Barriers

One highly effective method to guard against corrosion is the application of protective barriers on metal surfaces. These barriers prevent moisture and harmful substances from reaching and damaging the underlying metal. To maintain their protective qualities over time, it is important to maintain these coatings and reapply them as needed.

• Paints are commonly used to create a moisture-resistant barrier. They help shield metal surfaces from chemicals and environmental factors.
• Powder coatings provide a thicker, more durable layer of protection. They are particularly suited for outdoor applications where they face harsh conditions.

Additionally, using insulating materials to separate dissimilar metals further reduces the risk of galvanic corrosion. By combining protective coatings with these separation techniques, you can significantly enhance corrosion resistance.

• Plastic Washers and Bushings can be placed between bolts and metal surfaces to prevent electrical contact. Common materials include nylon or polyethylene.
• Rubber Gaskets are used in joints and flanges, rubber gaskets create a barrier that keeps metals from touching. This is particularly useful in piping systems.
• Insulating Sleeves can be applied around bolts or screws to prevent them from making contact with different metals.

Proteção Catódica

Cathodic protection is an effective technique used to prevent corrosion on metal structures, and it primarily comes in two forms: the Impressed Current System (ICS) and the Sacrificial Anode System.

• Impressed Current System (ICS)

The Impressed Current System employs an external power source to deliver a constant electric current, which helps shield metal structures from corrosion. A rectifier produces a direct current that passes through inert anodes positioned close to the metal being protected. This process reverses the electrochemical reactions, effectively converting the metal into a cathode and reducing the rate of corrosion.

This method is often used for pipelines, storage tanks, and marine vessels, especially in areas with high corrosion risk. Regular monitoring is essential to ensure that current levels are adequate and that the anodes function properly.

• Sacrificial Anode System

The Sacrificial Anode System protects metal structures by attaching a more reactive metal, like zinc or magnesium. This sacrificial anode corrodes preferentially, offering protection to the underlying metal. The idea is that the anode will corrode first, preventing damage to the protected structure.

It is extensively used in marine applications, including boats and ships, underground pipelines, and tanks. They provide an effective and economical strategy for preventing corrosion. However, it is important to perform regular inspections and replace the sacrificial anodes as needed, since they will gradually wear away over time.

Environmental Conditions Control

Controlling environmental conditions is crucial for slowing down galvanic corrosion. One effective approach is to manage the temperature and humidity of the surroundings. Lowering humidity can significantly reduce moisture exposure, which is a key factor in corrosion.

Additionally, using sealants around joints and connections can create a protective barrier. These sealants prevent moisture from entering and help shield sensitive components from exposure to corrosive elements.

Routine inspections are essential for effective corrosion management. Regular evaluations enable the early detection of corrosion indicators, allowing you to address issues promptly and prevent extensive damage from occurring.

Use Corrosion Inhibitors

Corrosion inhibitors are substances that can be introduced into the environment to help decrease the rate of corrosion. For instance, in cooling water systems, specific inhibitors can be added to create a protective layer on metal surfaces. This layer minimizes the metal’s reactivity and significantly slows the corrosion process, enhancing the longevity of the equipment.

Steel Types Needing Galvanic Corrosion Protection

Aço galvanizado: When paired with more noble metals like copper or stainless steel, the zinc coating on galvanized steel can corrode more quickly.

Aço carbono: Carbon steel corrodes easily in contact with stainless steel or copper, especially in humid or conducive conditions.

Aço de baixa liga: This type of steel is also prone to faster corrosion when paired with metals like aluminum, copper, or stainless steel.

Aço inoxidável: Although generally corrosion-resistant, some grades, like 304 stainless steel, can corrode when in contact with carbon steel in humid or salty environments.

Ferro fundido: Cast iron can suffer from galvanic corrosion when exposed to metals like stainless steel or copper, particularly in wet or marine conditions.

Hot-dip Galvanized Steel Is Better For Galvanic Corrosion

Hot-dip galvanized steel can still experience galvanic corrosion, but it has a thicker zinc layer for protection. This added thickness makes it more effective than other galvanized methods in light to moderate corrosion environments. If stronger protection is required, using dielectric fittings or applying additional coatings is recommended.

Steel Pro Group’s hot-dip galvanized steel products feature a thick and even zinc coating that provides superior protection against galvanic corrosion. We offer customizable options for coating thickness and additional treatments based on your project’s specific needs.

With our precise control over the galvanizing process, Steel Pro ensures that your materials are built to last for your project.