Corrosion protection means allow to extend the service life of the metal structure, as well as preserve its technical and physical properties during operation. Despite the variety of methods for ensuring anticorrosive action, it is possible to completely protect objects from rust damage only in rare cases.
The effectiveness of such protection depends not only on the quality of the tread technology, but also on the conditions for its use. In particular, to preserve the metal structure of pipelines, their best properties are demonstrated by electrochemical corrosion protection based on the operation of cathodes. The prevention of rust formation on such communications is, of course, not the only field of application of this technology, but in terms of the combination of characteristics, this direction can be considered as the most relevant for electrochemical protection.
General Information on Electrochemical Protection
Protection of metals from rust by means of electrochemical exposure is based on the dependence of the electrode potential of the material on the rate of the corrosion process. Metal structures should be operated in the range of potentials where their anodic dissolution will be below the permissible limit. The latter, by the way, is determined by the technical documentation for the operation of the structure.
In practice, electrochemical corrosion protection involves connecting a DC source to the finished product. An electric field on the surface and in the structure of the protected object forms the polarization of the electrodes, due to which the process of corrosion damage is also controlled. In fact, the anode zones on the metal structure become cathode, which allows you to shift the negative processes, ensuring the safety of the structure of the target object.
The principle of cathodic protection
There is a cathodic and anodic protection of the electrochemical type. The first concept, which is used to protect pipelines, still gained the most popularity. As a general principle, when implementing this method, a current with a negative pole from an external source is supplied to the object. In particular, in this way a steel or copper pipe can be protected, as a result of which the cathode sections will polarize with the transition of their potentials to the anode state. As a result, the corrosion activity of the protected structure will be reduced to almost zero.
At the same time, cathodic protection can have different versions. The above-described polarization technique from an external source is widely practiced, but the method of electrolyte deaeration with a decrease in the speed of cathodic processes, as well as the creation of a tread barrier, also works effectively.
It has already been noted more than once that the principle of cathodic protection is realized through an external current source. Actually, the main function of anti-corrosion protection lies in his work . Special stations perform these tasks, which, as a rule, are included in the general pipeline maintenance infrastructure.
Cathodic corrosion protection stations
The main function of the cathode station is to provide stable current to the target metal object in accordance with the cathodic polarization method. Use such equipment in the infrastructure of underground gas and oil pipelines, in water pipes, heating networks, etc.
There are many varieties of such sources, while the most common cathodic protection device provides for the presence of:
- current converter equipment;
- wires for connecting to the protected object;
- anode grounding conductor.
At the same time, there is a separation of stations into inverter and transformer. There are other classifications, but they are focused on the segmentation of installations either in the fields of application, or in terms of technical characteristics and input data parameters. The basic principles of operation are most clearly illustrated by the indicated two types of cathode stations.
Transformer installations of cathodic protection
It should be noted right away that this type of station is obsolete. Invertor analogs, which have both pluses and minuses, come to replace it. One way or another, transformer models are used even at new points of providing electrochemical protection.
As the basis of such objects, a low-frequency transformer at 50 Hz and a thyristor converter are used. The simplest devices are used for the thyristor control system, among which are phase-phase power controllers. A more responsible approach to solving management tasks involves the use of controllers with wide functionality.
Modern cathodic corrosion protection of pipelines with such equipment allows you to adjust the output current parameters, voltage indicators, as well as equalize protective potentials. As for the shortcomings of transformer equipment, they come down to a high degree of ripple of the output current at a low power factor. This flaw is not explained by the sinusoidal shape of the current.
The introduction of a low-frequency inductor into the system allows to solve the ripple problem to a certain extent, but its dimensions correspond to the dimensions of the transformer itself, which does not always make such an addition possible.
Inverter cathodic protection station
Inverter-type installations are based on pulsed high-frequency converters. One of the main advantages of using stations of this type is high efficiency, reaching 95%. For comparison, in transformer plants, this figure reaches an average of 80%.
Sometimes other virtues come to the fore. For example, the small dimensions of the inverter stations expand the possibilities for their application in complex areas. There are financial advantages, which are confirmed by the practice of using such equipment. So, invertor cathodic protection against corrosion of pipelines quickly pays off and requires minimal investment in technical content. However, these qualities are clearly noticeable only when compared with transformer plants, but today more effective new means of providing current for pipelines appear.
Designs of cathode stations
Such equipment is presented on the market in different cases, shapes and dimensions. Of course, the practice of individual design of such systems is also widespread, which allows not only to obtain an optimal design for specific needs, but also to provide the necessary operational parameters.
A rigorous calculation of the characteristics of the station allows us to further optimize the costs of its installation, transportation and storage. For example, for small objects cathodic protection against corrosion of pipelines on an inverter basis weighing 10-15 kg and a power of 1.2 kW is quite suitable. Equipment with such characteristics can also be serviced by a car, however for large-scale projects, more massive and heavy stations can be used, requiring the connection of trucks, a crane and teams of installers.
Protective function
Particular attention in the development of cathode stations is given to the protection of the equipment itself. For this, systems are integrated to protect the stations from short circuit and load breaks. In the first case, special fuses are used to handle emergency operation modes of plants.
As for voltage surges and breaks, the cathodic protection station is unlikely to seriously suffer from them, but there may be a danger of electric shock. For example, if in normal mode the equipment is operated with a small voltage, then after a break, the jump in performance can lead to 120 V.
Other types of electrochemical protection
In addition to cathodic protection, electric drainage technologies and tread corrosion prevention practices are also practiced. The most promising direction is considered to be a special protection from the formation of corrosion. In this case, active elements are also connected to the target object, which ensure the transformation of the surface with cathodes by means of current. For example, a steel pipe in a gas pipeline can be protected by zinc or aluminum cylinders.
Conclusion
Ways of electrochemical protection can not be attributed to new and, especially, innovative. The effectiveness of the application of such techniques in the fight against rusting has been mastered for a long time. However, the widespread use of this method is hindered by one serious drawback. The fact is that cathodic corrosion protection of pipelines inevitably produces so-called stray currents. They are not dangerous for the target structure, but can have a negative effect on nearby objects. In particular, stray current contributes to the development of the same corrosion on the metal surface of adjacent pipes.