What is meant by marine corrosion?

Answer 1

Corrosion means the breakdown of essential properties in a material due to chemical reactions with its surroundings. Marine corrosion is of particular interest to designers of ships and shoreline facilities because most metals used in these structures are vulnerable to damage from water, and sea water in particular. As an example, metals such as the reinforcing steel used in concrete structures will react in the presence of sea water forming rust that will expand and destroy the overlying concrete, leading to a premature failure of the structure. Different metals corrode more or less agressively in the presence of sea water, and materials scientists track this vulnerability in the "galvanic series", which is a chart that lists each material according to the severity at which it corrodes within a given environment. Note that bonding two metals together in a corrosive environment causes an electrochemical reaction between the two, which causes accelerated corrosion of the metal further down on the galvanic chart. (The metal further down the chart is known as the anode as is preferentially corroded. The other metal is refered to as the cathode.) To slow or limit corrosion of a particular piece of valuable metal (like a ship's hull or your hot water tank), engineers can attach a "sacrificial anode", which will corrode while protecting the structure in question. Another method of reducing corrosion in metal facilities (such as pipelines) is to provide a low level of electrical current to the facility in a system know as "cathodic protection" which protects the facility by accellerating corrosion to anodes driven into the ground at regular intervals. Rod Burrows, PE