Corrosion is an electrochemical reaction between a material and its environment which results in the deterioration or destruction of the material. Corrosion is not necessarily restricted to metals. In most circumstances metallic corrosion requires two factors in order for a reaction to occur: At least one metal An electrolyte such as water, soil or concrete [...]
Galvanic corrosion is corrosion that occurs when at least two metals are present and one metal corrodes(anode) in preference to another (cathode). The different metals must be electrically connected for this reaction to occur. Corrosion can often be attributed to the poor compatibility of selected materials where one metal corrodes in preference to another, creating [...]
Cathodic protection is a technique used to reduce the rate of corrosion of a metallic surface by making the metal the cathode. This can be achieved by attaching galvanic (sacrificial) anodes or impressed current anodes. Due to its extensive use in marine and other corrosive environments, steel is often the focus of Cathodic protection. Other [...]
As explained previously, galvanic corrosion occurs when two or more different metals are coupled together and are immersed in a common electrolyte such as sea water. However, we have all seen heavily corroded steel structures with no other metals connected. This type of corrosion occurs due to variations in stress levels placed on the structure [...]
This section provides a brief overview of galvanic anodes and how they apply to water craft. For further advice contact an accredited Marine Surveyor. Aluminium Vessels For aluminium used in hull construction, the primary aluminium is mixed with additional elements to create an alloy that has improved mechanical properties and greater corrosion resistance (e.g. Marine [...]
Anodes and Coating Systems Work Together Anodes and a good quality coating work best when applied together. The protective coating reduces the amount of DC current discharging from the hull by reducing the exposed surface area. When the coating starts to deteriorate over time, and more of the steel becomes exposed, the anodes offer protection [...]
Electrolytic corrosion is corrosion caused by current from an external source, such as a vessel’s battery or the shore power supply in a marina. This current is known as stray current. Electrolytic corrosion can cause serious damage to a vessel’s hull, underwater metallic components, coating systems and anodes. If an underwater inspection reveals unusually rapid [...]
Magnesium Alloy Anodes Magnesium anodes have a high negative driving potential which makes them suitable for the protection of steel structures where the environment has a high resistivity, such as in soil and fresh water. Magnesium anodes are used extensively for the protection of buried pipelines and also in hot and cold potable water [...]