If a component is still structurally sound, pitting corrosion can be eliminated manually by grinding or polishing, and the lost metal can be restored by weld build-up. To avoid degrading the qualities of the surrounding metal, the welding process must be properly prepared and carried out. The best results are obtained by using a filler material that will harden into a solid layer rather than a pool of liquid like silver or gold.
Components that are not structurally sound should be replaced before any attempt at repair. Replacement parts are available from many source after removal of any damaged components.
Pitting corrosion is an ongoing process that will continue to cause damage long after you have repaired a component. Regular inspections should be conducted to ensure that no further problems have arisen since the last inspection. If corrosion is detected, take the time necessary to locate its source and get it corrected.
Pitting corrosion can be avoided by using materials that are known to be resistant to the service environment. Temperature, pH, and chloride content are all adjustable. Cathodic and/or anodic protection can also be used to control pit formation. The use of protective coatings is also effective in preventing pit formation.
The most common cause of pit formation is oxygen exposure. If atmospheric air enters a copper conductor through a contamination or pinhole in the insulation, then copper will be oxidized at the point of entry. The resulting cavity will provide a location for future corrosion to start. This type of damage can occur anywhere within the electrical system. Covers and openings which allow air access should be sealed with gasketing material or metal-clad fiberglass tape.
Copper surfaces that are not exposed to air should be protected from oxidation by coating them with some sort of organic compound such as epoxy or acrylic resin. These types of coatings should always be applied according to manufacturer's instructions so they will provide adequate protection over time.
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When the cathode (damaged coating) is big and the anode (exposed metal) is small, pitting corrosion develops. Anodic: When a little amount of metal is exposed, it becomes anodic. When the fluid on the metal surface contains chloride, hypochlorite, or bromide ions, the pitting becomes violent. These chemicals damage the protective coating and cause more rapid deterioration of the metal underneath.
The anode may be any material that will corrode when in contact with the fluid. Iron, for example, would be an anode if it were in contact with acid. The anode creates holes in the coating by removing material from it. This leaves behind an uncoated spot that another current can flow through, causing more damage. Over time, this will lead to the entire anode being removed, exposing more metal to the acid which then begins to pit.
The cathode can be anything that has a lower potential than the anode. A zinc plate would be the anode in a battery, while a copper wire would be the cathode. The fluid itself may be any acid, such as hydrochloric, nitric, or phosphoric. Pitting will also develop in pipes, tanks, and other containers where water flows over the metal skin without coming into contact with any internal components.
If you have metal equipment used in acidic environments, check its maintenance schedule to ensure that no anodes have been removed.
Mechanical and chemical procedures are commonly employed to eliminate corrosion. Hand sanding using an abrasive mat, abrasive paper, or metal wool, as well as powered mechanical sanding, grinding, and buffing with an abrasive mat, grinding wheels, sanding discs, and abrasive rubber mats, are examples of mechanical techniques. Chemical methods include use of chemicals that will dissolve or inhibit corrosion when applied in appropriate concentrations.
Corrosion is a term used to describe the destructive reaction of a material exposed to air or moisture. Corrosion can be classified as either active or passive. Active corrosion occurs when there is an oxidation-reduction reaction (i.e., electron transfer) between a material and its surrounding environment. This typically results in formation of an oxide layer that protects the material from further attack. Passive corrosion does not involve an oxidation-reduction reaction and so cannot result in a protective oxide layer. Rather, it occurs because certain substances in air or water molecules have enough energy to break chemical bonds within the material itself, resulting in dissolution of the material into its constituent elements.
Materials most susceptible to corrosion include iron, steel, copper, and their alloys. Corrosion can also affect plastic and ceramic materials if they are exposed to oxygen at high temperatures for a long period of time. Corrosion can take place internally, within a component of the vehicle, or externally, on the vehicle's surface.