![]() ![]() Other factors – metal oxide layer formation, corrosion inhibitors, chemical reactions, physical and chemical homogeneity of the metal surface, and environmental effects (temperature, oxygen content, effect of electrode potential, etc.) 1, 2. Galvanic cells are more easily formed in immersion situations. On the other hand, industrial and marine environments may result in the presence of strong electrolyte materials containing a heavy amount of salts and ions. Generally, an anode-to-cathode surface ratio of at least 10:1 is recommended to minimize galvanic corrosion 8.Īggressiveness of the electrolyte or installation environment – in many atmospheric applications, rainwater and dew are the primary electrolytic materials, but they do not contain many salts and ions which would make them highly conductive. For example, avoid the use of galvanized fasteners to combine cathodic metals such as carbon steel, copper, or stainless steel. Zinc-to-Metal Surface Area Ratio – Avoid combining a small area of galvanized steel with a large area of cathodic metal. ![]() Galvanic Series of Metals in Saltwater noting Electrical Potential Energy (in Volts) (Ref. Actual electrical potential values will vary depending on the specific electrolyte present if not saltwater 4. Generally, severity of corrosion increases when combining galvanized steel with metals far away from zinc in the galvanic series. Primary Factors Affecting Rate of Galvanic Corrosionĭifference in electrical potential – Refer to the figure below for a Galvanic Series containing values for electrical potential of various metals in a saltwater application 8. Maintenance of the paint is required to minimize exposure of the anode. Painting both metals is preferred to avoid accelerated corrosion concentrated in the areas of coating imperfections on the anodic metal. ![]() This method is specified when electrical isolation is not feasible (slip critical connections, welded connection, etc.). In atmospheric exposure or immersion conditions, application of a durable paint system can minimize exposure of the connection to the electrolytes in the environment. Removal of Electrolyte Exposure – installation in sheltered conditions such as the interior of climate-controlled buildings does not typically result in galvanic corrosion.Corrosion-inhibiting pastes, dried adhesives, and sealants are also utilized where practical. Common materials include neoprene, rubber, plastic, Mylar, nylon, Teflon, glass reinforced epoxy (GRE) gaskets, and more. Removal of Return Current Path (Electrical Isolation) – utilize electrically inert spacer materials with a very low ability to absorb moisture.Replace the Anode or Cathode – where the combination of dissimilar metals cannot be avoided, specify combinations which minimize the difference in electrical potential.To prevent galvanic corrosion from occurring, one element of the corrosion cell must be interrupted: A common example is ordinary moisture such as water, rain, dew, snow, high humidity, or sea spray. Electrolyte – conductive medium that allows electrons to be transferred from anode to cathode.direct contact) between the anode and cathode. Return Current Pathway – electrical connection (e.g.Cathode – metal of less negative electrical potential, where electrons are received.Anode – metal of greater negative electrical potential, where electrons are generated by the reaction.The formation of a galvanic cell requires all the following components to be present 1: However, just because dissimilar metals are in contact does not mean galvanic corrosion will occur. This results in accelerated corrosion of the metal losing electrons while the metal receiving electrons is preserved. An electrochemical reaction occurs involving a transfer of electrons from one metal to the other (electric current) when the two metals are connected by an external, conductive path. The galvanic cell is similar to a battery, consisting of two dissimilar metals immersed in an electrolyte solution. ![]()
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