What is corrosion? It is the gradual degradation of material, normally metals, by chemical reaction with its environment. Rusting is the formation of iron oxides and is a common example of electrochemical corrosion. Corrosion can also occur in ceramics or polymers. Corrosion adversely impacts the positive properties of materials and structures like strength, appearance and permeability.
Corrosion occurs on exposed surfaces. Therefore, methods for corrosion control are passivation and chromate conversion, which increases a material's corrosion resistance.
Corrosion protection methods
Some of the corrosion protection measures are surface treatments, applied coatings and galvanization.
Galvanization: Plating, painting, and the enamel application are the most common anti-corrosion treatments. Theseprovide a layer of corrosion-resistant material between the environment and the structural material. Sometimes there may be trade-off in mechanical flexibility versus resistance to abrasion and high temperature. Painting with roller or brush should be done for tight spaces, while spray would be better for larger coating areas such as steel decks and waterfront applications. Flexible polyurethane coatings provide an anti-corrosive seal with a highly durable slip resistant membrane. Painted coatings are relatively easy to apply and enables effective corrosion control.
Reactive coatings: If the environment is controlled, corrosion inhibitors areoften added to it. These form an electrically insulating or chemically impermeable coating on exposed metal surfaces, to suppress electrochemical reactions. Chemicals that inhibit corrosion include chromates, phosphates, polyaniline, other conducting polymers and a wide range of specially-designed chemicals resembling surfactants.
Anodization: Aluminium alloys often undergo surface treatment. Anodizing is very resilient to weathering and corrosion, so it is commonly used for building facades. However, it must be cleaned frequently, without which panel edge staining will naturally occur.
Biofilm coatings: This is a new method of corrosion protection which has been developed by applying bacterial films to the metalsurface in highly corrosive environments. This process increases the corrosion resistance substantially. Alternatively, antimicrobial-producing biofilms can be used to inhibit mild steel corrosion.
Controlled permeability formwork (CPF): This is a method of preventing the corrosion of reinforcement by naturally enhancing the durability of the cover during concrete placement. CPF has been used in environments to combat the effects of carbonation, chlorides, frost and abrasion.
Cathodic protection: This method is another technique for corrosion control of a metal surface. These systems are most commonly used to protect steel, water, and fuel pipelines and tanks; steel pier piles, ships, and offshore oil platforms.
Sacrificial anode protection: This method is used mostly in the hull of a ship.
Practically it is not usually possible to completely eliminate all corrosion damage to metals used for construction in an industrial plant. If suitable water treatment with corrosion inhibitors is used, a life of at least twenty years might be expected. Engineers often add a "corrosion allowance" to the metal thickness, permitting a certain amount of thinning. Removal of oxygenfrom water systems in the pH range 6.5-8.5 is one of the best ways to eliminate corrosion.
