cathodic and protective protection of metals against corrosion

cathodic and protective protection of metals against corrosion Protective protection of metals from corrosion - features

Protective protection of pipeline metals from corrosion is a kind of metal to prevent exposure to negative external factors that cause metal destruction.

Widely used against rust formation on the main pipeline for various purposes.

This type of processing is available even to enterprises that do not have sufficient funds.

General information

Causes of corrosion

The appearance and growth of pipeline corrosion occurs when the metal is oxidized from the constant influence of a humid environment. The metallic composition changes at the ionic level.

This process can be influenced by the composition of the fluid that flows inside the pipeline.

The reasons for the appearance of rust can be as follows:

  • The alloys of which the pipelines are made have different potentials of an electrochemical type. This will cause currents to flow through the pipes. The potential difference arises when the constituents of the soil change, as well as various parameters of environmental indicators.
  • Moisture or groundwater present in the soil.

  • Chemical soil composition, including the presence of acid-type impurities in the environment.
  • The composition of the liquid that is transported through the pipeline.
  • The presence of a stray current in the ground.

Please note that in order to perform anti-corrosion protection, the characteristics that affect the metal surface should be evaluated.

About varieties

There are several types of corrosion of metal pipes:

  • Surface, which spreads over the entire area of ​​the pipes.

  • Local, which is located in separate areas.
  • Crevice that appears in small cracks.

Local corrosion is most alarming, because the bulk of damage is precisely because of its appearance. The development of a slotted one is also popular, but it will not lead to significant damage to the material. The likelihood of corrosion in a larger direction is given to pipe sections, which are continued under railway crossings or under the supports of overhead electric transmission lines.

The rate of development of the process ranges from 0.3 to 3 cm per year.

Overview of species

What is chemical corrosion

This process appears in non-conductive media. They can be gases, alcohol compounds and petroleum products. As the temperature rises, the rate of corrosion propagation increases.

Rust can form on ferrous or non-ferrous metals. Aluminum products under the influence of corrosion factors are covered with a thin film, which will then provide a protective system and create an obstacle to the development of the oxidation process.

Please note that copper under the influence of this type of corrosion begins to turn green, and the resulting oxide film in a humid environment may not always contribute to the creation of a barrier against rust, and as an exception, when the metal structure the same with the film structure.

Alloys can be susceptible to another type of rust, that is, there are elements that do not undergo oxidation, but, on the contrary, they are reduced. For example, at elevated temperature characteristics and elevated pressure, carbides are reduced, but the required qualities are lost.

Electrochemical corrosion

Protective method of protecting metals from corrosion is achieved only when the surface is in contact with electrolyte, erroneously. A thin film based on the material is enough to cause corrosion. The reason for this type of rust will be the use of technical or table salt. For example, if snow is spreading on the road, then cars and pipelines that are laid underground suffer. The process of origin is as follows:

  1. cathodic and protective protection of metals against corrosion Atoms (partly) are lost in the joints of metal structures, their transition to an electrolytic solution is carried out, that is, the formation of ions will occur.

    Atoms replace electrons, they will charge the material with negative charge, and thus positive charges will accumulate in the hotplate.

  2. Corrosion of the electrochemical type is caused by stray currents, which, when leaking from the electrical circuit, go into soil or water solutions, and then into the metal structure itself. The specific places where rust appears will be those areas from where stray currents enter the water.

How to create such protection?

How to provide protective protection

Coating pipes with special compounds is not a task only the manufacturer, and in the process of applying the structure, ensuring the protective properties must also be carried out. In total, there are several methods of protecting a metal surface from the effects of an aggressive environment:

  • Chemical processing.

  • Coating the walls with special compounds.
  • Protection against stray currents.
  • Connecting the anode or cathode.

It is interesting that the method of protecting pipelines from corrosion will be popular in organizations that install and operate a pipeline mode of transport.

Passive and active methods

Corrosion protection is a whole complex of measures that are carried out by enterprises.

Passive methods of protection will involve the implementation of such works:

  • At the stage of installation, an air gap is left between the soil and the pipeline, which prevents the ingress of groundwater, including those with alkaline and acid impurities.
  • Coating with special compounds, the purpose of which extends from aggressive soil influences.
  • Treatment of metals with chemical compounds, with the appearance of a thin film.

Active protection methods involve the use of current and ion exchange based on chemical reactions, due to which they are used:

  • Protection of underground pipelines from corrosion by making an electric drainage system for insulation pipeline transport from stray currents.
  • Anode protection against destruction of metal surfaces.

  • Cathodic protection to increase the resistance of metal substrates.

Only taking into account all methods that prevent the formation of rust on the metal, and the service life of structures will be increased. Anticorrosion protection of the pipeline must be performed in a complex manner.

Advantages of using protectors

The essence of protective metal protection against corrosion is that the method gives many advantages. Pipe protection in this way is carried out with the addition of an inhibitor.

Such a material with a negative electrical charge. Under the influence of air masses, it will dissolve, and the structure will remain intact and will not undergo rusting. Protective anticorrosion protection is used to extend the life of building structures, heating systems and water supply, as well as main and field transport of the pipeline. The use of an electrochemical type of protection allows you to eliminate the causes of a large number of types of corrosion. Such corrosion protection is a good solution even for those enterprises that do not have the financial ability to provide 100% protection from an uncontrolled process.

To ensure the literacy of the approach, you need:

  1. Protectors made of aluminum, used in the environments of sea waters and offshore shelves near the coast.
  2. In environments with low electrical conductivity, use magnesium protectors. But still they are not suitable for the treatment of the inner coating of tanks, oil settling tanks due to the fact that they have a sufficiently low level of explosion hazard.
  3. Use protectors to protect the environment from environments with fresh water.
  4. Zinc based protectors are safe and can be used for explosive and fire hazardous industries.

The following number of advantages can be added to anti-corrosion protection protection:

  • Lack of money and production capacity of the enterprise will not be an obstacle to its implementation.
  • Ability to protect small structure.
  • If pipes are covered with thermal insulation materials, this protection will be acceptable.

What is used for this?

Materials used and purposes of use

cathodic and protective protection of metals against corrosion Corrosion protection is required for all metal substrates. This type of resistance to rust is widely used for the treatment of tankers, because these vessels are more susceptible to water influences, which contain aggressive components.

Even special paint cannot cope with such a problem.A rational choice for coating steel structures is to use protectors with negative potential. Zinc, magnesium and aluminum are used in the manufacture of devices.

A large potential difference between steel and metal surfaces will increase the spectrum of protective effects, due to which different types of corrosion are eliminated. Protective systems are based on the specifics of the protectors and the environments in which they will be used.

Passive protection is required for coatings of steel and metal products. The essence of the method lies in the use of galvanic anodes, which provide resistance to rust underground pipelines. When calculating for such an installation, one should take into account such indicators as the parameters of the current strength, the resistance from voltage drops, the properties of the protective degree used for 1 km of the pipeline and the indicator of the distances between the protective elements.

Methods of protection of pipelines

Corrosion of the pipeline appears during use. The appearance of rust can be inside and outside the pipes, and deposits appear on the inside, and the reason for this will be chemical reactions of the composition of the transported liquid with the metal.

The surface condition will be influenced by a high soil moisture index.

If you do not provide protective protection of metals from corrosion in time, a number of consequences may appear. Important:

  • Routine inspections are recommended at short intervals.
  • Repair work is carried out periodically, regardless of the presence of corrosion.
  • The operation of the pipeline transport is inevitably suspended, because it is necessary to carry out inspections and carry out scheduled preventive and other important repair work.

Important! To ensure complete protection, it is required to take into account the installation method, contact with an aggressive environment, and also the type of pipeline.

Protective protection

In practical activities there are situations when it is necessary to perform anti-corrosion protection of previously painted pipelines. The tread method, together with the application of paints and varnishes, is considered a passive way to prevent the appearance of metal corrosion.

The efficiency of this method is not so high, but it also has many advantages:

  • There are flaws in the entire structure of the pipeline transport, which are quite easy to identify.
  • The consumption of materials is greatly reduced, but protection on the pipes will be provided for a long time.

  • The current required to protect the surface is distributed evenly.

A big plus for the protection of paintwork will be the distribution of the protective flux over the surface, where special attention is required.

Treatment against corrosive liquids

Internal pipeline damage appears after exposure to negative media.The water can contain bicarbonates or carbonates, as well as oxygen, which will be the primary cause of corrosion. Purification in the pipeline does not give the expected result, as it is technically difficult, expensive and almost unrealistic.

The ideal solution would be pretreatment of water, i.e. removal of aggressive media and turning them into a solution with a low calcium content. This is achieved simply - soda, calcium and sodium carbonate are added to the water. It is important to take into account that in areas from separate points of the water intake, the liquid is treated with the addition of polyphosphates.

Please note that such protection of underground tanks made of zinc materials is done with the addition of silicates, phosphates and polycarbonates to solutions. This creates a thin film that prevents rusting.