Rahavard Zob Iranian

Corrosion of metals in aqueous environments is almost always electrochemical in nature . t occurs when tow or more electrochemical reactions take place on a metal surface . As a result some of the elements of the metal or alloy change from a metallic state in to a nonmetallic state .the products of corrosion may be dissolved or solid corrosion products ; in either case , he energy of the system is lowered asthenetal canvets to alower-energy form.

Rusting of steel is the best kown example of concersion of a metal (Iron) into a nonmeticallic corrosion product (Rust) .The changein the energy of the system is the driving force for the corrosion process and is a subject of thermodynamics .

The electrochemical rections occur uniformly or nonuiformly on the surface of themetal , which is called an electrod . The ionically conducting liquid is called an electrolyte . As a result of the reaction , the electrode/electrolyte interface acquires special structure , in which such factors as the separation of charges between electrons in the metal andions on the electroe , and diffusion of species all play important roles .

One of he important features of the electricfied interface between the electrode and electrolyte is appearance of the potential difference a cross the double layer , which allows the definition of the electrode potential .

The electrode potential ecomes one of the most important parameters in both of the thermodynamics and the kinetics of orrosion .

One of the best ways to corrosion control isCathodic Protection .

Rahavard Zob engineeringgroup has statedto proe in corrosion control and cathodic protection since 1999 . Also this company is equipping it`s laboratories , n addition this group has improved in promotion of quality and producing differet kindof cathodic protection equipment .

Cathodic protection is an electrochemical means of corrosion control in which the oxidation reaction in a galvanic cell is concentrated at the anode and soppreses corrosion of the cathodic in the same cell . Figure A . shows a simple cathodic protection system . the steel pipeline is cathodically protected by its connection to a acrificial magnesium anode buried in the same soil electrolyte .

Cathodic Protection was first suggested by Sir Humphrey Davy in the 1820 as means of controlling corrosion on British noval ships . It became common in the 1930 on the Gulf Coast of the United States , where it was used to control the corrosion of pipelines carrying high pressure hydrocarbons .

Much of the terminology f cathodic protection still related to corrosion control of onshore buried steel pipelines . Virtually all modern pipelines are coated with an organic protective coating that is supplemented by cathodic protection system sized to provent corrosion at holidays in the protective coating .

This combination of protective coating and cathodic protection is used on virtually all immersed or buried carbon steel structures , with the exception of offshore petroleum production platform and reinforced concrete structure . Offshore latforms are usually uncoated but cathodically prorected .

Cathodic protection causes changes in the chemistry of seawater near the protect structure , and this causes the precipitation of a natural coating on the structure that reduces the need for cathodic protection current .

Concrete structure normally relay on the protectiveness of the concrete cover to prevent the corrosion embedded steel .Cathodic protection is some times used to extend the life of the already deteriorated structures .

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