What is Corrosion?

What is Corrosion?

Corrosion is the deterioration of a metal as a result of chemical reactions between it and the surrounding environment. Both the type of metal and environmental conditions, particularly corrosive liquids in contact with metal in pipelines, determine the form and rate of deterioration.

The main corrosion is generated when the materials are immersed in a liquid medium, as it would be in the case of a reactor where there are chemical reactions of different compounds, which can be liquid,

What metals corrode?

All metals can corrode. Some, like pure iron, corrode quickly. However, stainless steel, which combines iron and other alloys, corrodes more slowly and is therefore used more often.

All the small groups of metals, called noble metals, are much less reactive than others. As a result, they rarely corrode. In fact, they are the only metals that can be found in nature in their pure form. Noble metals, not surprisingly, are often very valuable. They include rhodium, palladium, silver, platinum, and gold.

types of corrosion

General attack corrosion:

Also known as uniform attack corrosion, general attack corrosion is the most common type of corrosion and is caused by a chemical or electrochemical reaction that results in the deterioration of the entire exposed surface of a metal. Eventually, the metal deteriorates to the point of failure.

General attack corrosion accounts for the largest amount of metal destruction from corrosion, but is considered a safe form of corrosion, due to the fact that it is predictable, manageable, and often avoidable. Localized Corrosion:

Localized Corrosion:

Unlike general attack corrosion, localized corrosion is specifically directed at one area of ​​the metal structure. Localized corrosion is classified as one of three types:

Bites:

Pitting occurs when a small hole or cavity forms in the metal, usually as a result of depassivation (Increased corrosion rate of a passive metal) of a small area. This area becomes anodic, while some of the remaining metal becomes cathodic, producing a localized galvanic reaction. Deterioration of this small area penetrates into the metal and can lead to failure. This form of corrosion is often difficult to detect due to the fact that it is generally relatively small and may be covered and hidden by corrosion compounds.

crevice corrosion:

Similar to pitting, crevice corrosion occurs in a specific location. This type of corrosion is often associated with a closed site, such as those under gaskets, washers, and clamps. Acidic conditions or oxygen depletion in a crevice can lead to crevice corrosion.

Filiform corrosion:

Occurring under painted or plated surfaces when water breaks down the coating, filiform corrosion begins with small defects in the coating and spreads to cause structural weakness.

Galvanic corrosion:

Galvanic corrosion, or dissimilar metal corrosion, occurs when two dissimilar metals meet together in a corrosive electrolyte. A galvanic couple is formed between the two metals, where one metal becomes the anode and the other the cathode. The anode, or sacrificial metal, corrodes and deteriorates faster than it would alone, while the cathode deteriorates more slowly than it otherwise would.

Three conditions must exist for galvanic corrosion to occur:

  • Electrochemically dissimilar metals must be present
  • Metals must be in electrical contact
  • These metals must be exposed to an electrolyte.

Environmental cracking:

Environmental cracking is a corrosion process that can result from a combination of environmental conditions that affect the metal. Chemical, temperature, and stress-related conditions can cause the following types of environmental corrosion:

  • Stress Corrosion Cracking (SCC)
  • corrosion fatigue
  • Hydrogen induced cracks
  • Liquid metal brittleness

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