Cathodic Protection - It is an electrochemical technique used to prevent and control the corrosion of various types of metallic structures and plants. (Read more details in following text)
Visit Metec Group Products area (sacrificial anodes, zinc anodes, aluminium anodes, offshore corrosion control, marine corrosion control) for details.
Cathodic Protection: What is ?
Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making it work as a cathode of an electrochemical cell. This is achieved by placing in contact with the metal to be protected another more easily corroded metal to act as the anode of the electrochemical cell. Cathodic protection systems are most commonly used to protect steel, water or fuel pipelines and storage tanks, steel pier piles, ships, offshore oil platforms and onshore oil well casings. Cathodic protection can be, in some cases, an effective method of preventing stress corrosion cracking.
Cathodic Protection: Types
Galvanic Cathodic Protection
Today, galvanic or sacrificial anodes are made in various shapes using alloys of zinc, magnesium and aluminium. The electrochemical potential, current capacity, and consumption rate of these alloys are superior for Cathodic Protection than iron. Galvanic anodes are designed and selected to have a more "active" voltage (technically a more negative electrochemical potential) than the metal of the structure (typically steel). For effective Cathodic Protection, the potential of the steel surface is polarized (pushed) more negative until the surface has a uniform potential. At that stage, the driving force for the corrosion reaction is halted. The galvanic anode continues to corrode, consuming the anode material until eventually it must be replaced. The polarization is caused by the current flow from the anode to the cathode. The driving force for the Cathodic Protection current flow is the difference in electrochemical potential between the anode and the cathode.
Impressed current Cathodic Protection
For larger structures, galvanic anodes cannot economically deliver enough current to provide complete protection. Impressed current cathodic protection (ICCP) systems use anodes connected to a DC power source (a cathodic protection rectifier). Anodes for ICCP systems are tubular and solid rod shapes or continuous ribbons of various specialized materials. These include high silicon cast iron, graphite, mixed metal oxide, platinum and niobium coated wire and others. A rectifier connected to a pipeline. A typical ICCP system for a pipeline would include an AC powered rectifier with a maximum rated DC output of between 10 and 50 amperes and 50 volts. The positive DC output terminal is connected via cables to the array of anodes buried in the ground (the anode groundbed). For many applications the anodes are installed in a 60 m (200 foot) deep, 25 cm (10-inch) diameter vertical hole and backfilled with conductive coke (a material that improves the performance and life of the anodes). A cable rated for the expected current output connects the negative terminal of the rectifier to the pipeline. The operating output of the rectifier is adjusted to the optimum level after conducting various tests including measurements of electrochemical potential.
Galvanized steel
Galvanizing generally refers to hot-dip galvanizing which is a way of coating steel with a layer of metallic zinc. Galvanized coatings are quite durable in most environments because they combine the barrier properties of a coating with some of the benefits of cathodic protection. If the zinc coating is scratched or otherwise locally damaged and steel is exposed, the surrounding areas of zinc coating form a galvanic cell with the exposed steel and protect it from corrosion. This is a form of localized cathodic protection - the zinc acts as a sacrificial anode.
Antifouling System
WWI's Chlorematic® Antifouling System creates an antifouling solution, sodium hypochlorite, directly from seawater and distributes it through the seawater cooling system thus preventing the growth of all types of marine fouling. This sodium hypochlorite solution is extremely effective against both macro (barnacles, mussels, etc) and micro (algae, slime, bacteria, etc) fouling. More importantly, it is not harmful to the environment as it is reversible, turning back to salt and water once the process is complete. WWI's Chlorematic® systems are custom-designed to suit all types of vessels and their individual needs.
Cathodic Protection, Impressed current cathodic protection (ICCP), Corrosion Prevention Control