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Galvanic corrosion of metal washer

Galvanic Corrosion

What is Galvanic Corrosion?

The Basics of Galvanic Corrosion

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The Basics of Galvanic Corrosion

Galvanic corrosion can be succinctly defined as the corrosion damage that takes place when two dissimilar metals or alloys come into electrical contact in the presence of an electrolyte, leading to an accelerated corrosion rate of the less noble (or more anodic) metal, while the more noble (cathodic) metal remains relatively protected. This phenomenon can be envisioned as a battery, where one metal acts as the anode and corrodes, and the other acts as the cathode and is protected.
In the realm of metallurgical science, galvanic corrosion emerges as one of the most fundamental yet intricate phenomena causing significant deterioration and failure of metal structures. This type of corrosion, often described as a ‘bimetallic couple’ or ‘dissimilar metal corrosion,’ is especially prevalent in multi-metal environments where different metals or alloys are in direct or indirect contact, catalyzing the degradation of the more anodic material.

Several variables dictate the severity and rate of galvanic corrosion.

  • The Galvanic Series: The galvanic series for a given environment is a list of metals and their associated EMF values. When the EMF values are too far apart, the metal with the higher EMF will corrode.
  • Area Ratio: The relative surface areas of the cathodic and anodic metals play a significant role. A small anode coupled with a large cathode is a recipe for rapid anodic corrosion.
  • Electrolyte Properties: The nature, concentration, temperature, and oxygen content in the electrolyte can affect galvanic corrosion rates. Typically, a high concentration of ions, elevated temperatures, and increased oxygen content can enhance the corrosion rate.
  • Duration and Wetness: An electrolyte must be present for galvanic corrosion to occur. Metals that remain wet for extended periods are more susceptible.

To curb or minimize the effects of galvanic corrosion, various strategies can be adopted:

  • Material Selection: Whenever possible, select metals that are close together in the galvanic series for applications involving metal contact in corrosive environments.
  • Cathodic Protection: This involves making the metal that needs protection act as a cathode by introducing an external anode that will corrode in its place.
  • Coatings: Protective coatings, when applied correctly, can shield the metal from the environment, thus preventing the electrolyte from making contact.
  • Control Electrolyte Composition: By altering the electrolyte composition or using inhibitors, the corrosion rate can be reduced.
  • Design Considerations: Ensure that if galvanic corrosion does occur, the anodic area is much larger than the cathodic area. This reduces the corrosion rate.

Armoloy's Solution to Corrosion

Armoloy offers multiple metal surface treatments with varying levels of protection from the common causes of corrosion. Offering both broad-spectrum and industry-specific applications, our protective metallic coatings add significant value through increased performance and decreased revenue losses from unplanned maintenance and downtime.

Our protective coatings ensure a thin, precise coat that won’t impact production, but will improve surface hardness and prevent environmental defects. Beyond increasing wear life, Armoloy tailors our metallic coatings based on the specific requirements of your application and industry.

Galvanic corrosion, with its intricacies and broad influence, necessitates an in-depth comprehension for those involved in design, construction, and maintenance of metallic structures. Recognizing its mechanism, influencing variables, and adopting a proactive approach in its mitigation can significantly enhance the lifespan and reliability of these structures, saving both time and resources in the long run.

Beyond the Lab: Metal Failures in Narrative Form

Other Metal Failure Modes

Other common metal failures include:

Galvanic corrosion can also result from, or be a precursor to, other potential metal failures

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