What is pitting corrosion?
Pitting corrosion is a localized form of corrosion by which cavities or “holes” are produced in the material. Pitting is considered to be more dangerous than uniform corrosion damage because it is more difficult to detect, predict and design against. Corrosion products often cover the pits.
Which factors influence the pitting corrosion?
Problems with pitting corrosion attacks depend primarily on the chloride content, the pH value (the acidity), and the temperature. If pitting has taken place and if the environment in such is not too corrosive for the steel grade, a spontaneous repair of the passive layer will occur in the presence of oxygen.
Can the process of corrosion be stopped with cathodic protection?
Cathodic Protection Another way to protect against corrosion is to confer a continuous negative electrical charge on a metal. This method is referred to as cathodic protection. Cathodic protection replicates the effects of a sacrificial coating but with a more active metal.
How can pitting corrosion be prevented?
Pitting corrosion can be controlled by:
- Use of a coating that will prevent pitting on metal surfaces.
- Using more corrosion resistant materials.
- Ensuring that the fluids in contact with the material is washed away regularly.
- Use of cathodic protection.
- Avoiding stagnant zones.
- Inhibitor use / fluid chemistry control.
How do you get rid of pitting corrosion?
If a component is still structurally sound, pitting corrosion can be mechanically removed by grinding or polishing and the missing metal replaced by weld build-up. Care must be taken to prepare and undertake the welding process carefully, to avoid reducing the properties of the surrounding metal.
How does pitting occur?
Pitting corrosion occurs when the cathode (damaged coating) is large and the anode (exposed metal) is small. Typically the surface protection layer or film becomes the cathode when it is damaged and cracked. A small area of metal is then exposed and becomes the anodic.
Where does pitting occur?
What is cathodic protection used for?
Cathodic protection is commonly used to protect numerous structures against corrosion, such as ships, offshore floaters, subsea equipment, harbours, pipelines, tanks; basically all submerged or buried metal structures.
How does cathodic protection protect metals from corrosion?
Corrosion is an electrochemical process, normally occurring at the anode but not the cathode. The principle of cathodic protection is to connect an external anode to the metal to be protected and to pass a DC current between them so that the metal becomes cathodic and does not corrode.
What is cathodic protection and how does it work?
Cathodic protection (CP; / k æ ˈ θ ɒ d ɪ k / ()) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded “sacrificial metal” to act as the anode.The sacrificial metal then corrodes instead of the protected metal.
How does DC current work in cathodic protection?
Cathodic protection is the use of DC Current from an External Source to oppose the discharge of corrosion current from anodic areas of the structure. It minimizes the potential difference between anode and cathode and in turn reduces corrosion.
When is cathodic protection needed?
Cathodic protection systems are employed in numerous industries to protect a broad range of structures in challenging or aggressive environments. The oil and gas industry, in particular, uses cathodic protection systems to prevent corrosion in fuel pipelines, steel storage tanks, offshore platforms, and oil well casings.
How to check cathodic protection rectifier?
– A power source for impressed current cathodic protection – DC cables – Groundbed – Protected structure