Talking about the Corrosion of Chemical Equipment and the Design and Application of Anti-corrosion Measures
2021-07-14
1. The cause and classification of corrosion of chemical equipment
Under normal circumstances, due to the particularity of the environment in which chemical equipment is used, it is generally a metal product. For metal, its structure is extremely prone to corrosion. The external environment such as temperature, humidity, and air will directly cause corrosion of the metal. phenomenon. In an industrial environment, especially in chemical companies, some oxidation-reduction gases and media are involved in production. In addition, the humidity and temperature in the production workshop are relatively high, so strong chemical reactions will occur on the surface of the metal. , Thereby forming corrosion.
For the classification of corrosion, there are generally two classification methods. One is to classify according to the mechanism of corrosion, and the other is to classify according to the cause and appearance of corrosion. According to the mechanism of corrosion, it can be divided into electrochemical corrosion and chemical corrosion. Electrochemical corrosion mainly refers to the corrosion phenomenon caused by the electrode reaction on the surface of the metal material after contact with the electrolyte solution. This reaction is generally an oxidation-reduction reaction, and the main factors are the humidity and temperature of the environment; Chemical corrosion refers to a relatively strong chemical reaction between the metal surface and the surrounding medium, which causes the metal to be damaged to a certain extent. The main reasons for this corrosion are high temperature and dry environment. According to the appearance and cause classification of corrosion, it can be divided into delamination corrosion, industrial atmospheric corrosion, high temperature oxidation corrosion and marine atmospheric corrosion.
2. Corrosion mechanism of chemical equipment
1. The mechanism of electrochemical corrosion
Metals are prone to electrochemical corrosion, mainly due to a series of electrochemical interactions between the surface of the metal and the ionic conductive medium, which damages the surface of the metal. All electrochemical corrosion will include at least an anode reaction and a cathode reaction, and at the same time, the electron flow inside the metal will exchange with the ion flow in the medium. The anode reaction is an oxidation process in which metal ions are transferred from the metal to the medium, and corresponding electrons are emitted at the same time, and the chemical valence changes, and then the electrons combine with the ions in the proton. The cathode reaction is a reduction reaction, in which the oxidant composition in the medium undergoes a reduction reaction by absorbing electrons from the anode. Since electrochemical corrosion does not perform external work on the electron flow, it will consume points inside the corroded battery, so electrochemical corrosion will gradually accelerate the corrosion rate.
2. Industrial atmospheric corrosion mechanism
In those environments where industrial pollution is more serious, the air contains more volatile substances such as sulfides, carbon dioxide, and hydroxides, and also contains some industrial dust, which are prone to corrosion media. When these media are in a humid environment, acid gases will combine with water to form inorganic acids. These acids have strong corrosive properties, so they will induce corrosion. In an industrial atmosphere, equipment is caused by the combined effects of electrochemical corrosion and direct chemical corrosion. The essence of all corrosion is actually an oxidation process in which metal elements form ions after losing electrons. The main difference between electrochemical corrosion and industrial atmospheric corrosion is the environment in which they occur.
3. Design and application of anti-corrosion measures for chemical equipment
1. Reasonable selection of materials, optimized design
The corrosion of equipment is closely related to the material of the equipment. In the selection process of chemical materials, it is necessary to focus on the occurrence of corrosion, pay attention to the reasonable selection of materials, and fully consider the nature of the medium, the temperature of the environment and the operating pressure, etc., according to the chemical industry The requirements of raw materials are designing the structure and type of equipment. The structural design should focus on the production requirements and stress characteristics in the production and operation of chemical equipment, and the following aspects should be paid attention to in the design: the structural requirements of the product should be consistent with the corrosion resistance requirements of the production of chemical products; secondly, attention should be paid to the chemical industry. The operation stability and smoothness of the equipment, to prevent the suspension of corrosive media, insufficient heat load distribution, steam condensation and accumulation of corrosion products; attention should be paid to the protection of external forces to prevent alternating stresses. Fatigue corrosion.
2. Environmental anti-corrosion treatment methods
Environmental anti-corrosion treatment is to reduce the corrosion effect by changing the environment within the range of conditions that do not affect the production process. It can be mainly through the following aspects: First, the removal of corrosive substances in the environment. Removal of corrosive substances in the environment, including the removal of moisture, oxygen and other harmful components in the environment, oxygen can be removed by adding deoxidizers, and dehumidification can be used to keep the metal surface above the dew point, and to control the moisture in the device Below a certain index; the second is to add anti-corrosion additives. Preservatives can be added so that a certain protective film can be formed on the surface of the metal, thereby significantly inhibiting the corrosion of the metal surface to achieve the purpose of anti-corrosion. Common preservatives include nitrite, complex acid salts, thiobenzene, etc., which are in use For these additives, the added concentration must be very strict.
3. Anti-corrosion measures for surface coating
It is common to paint, which is an intuitive anti-corrosion measure. The commonly used anti-corrosion paint is oil paint, such as phthalic acid resin, epoxy resin, polyvinyl butyral + phosphoric acid, etc., in order to achieve better anti-corrosion purposes, usually not only the paint film Strict requirements for anti-rust ability, mechanical properties and aging properties of the paint also need to have a full understanding of the properties, surface conditions, construction environment and use conditions of the painted objects. The other is anti-corrosion through metal coating. There are usually two types of metal coatings. One is the use of plug welding, welding lining, and metal composite methods in the coating material. This prevention has a long service life because the coating has good corrosion resistance and is thicker. However, the process requirements are more stringent; the other is to achieve the purpose of anti-corrosion through sacrificial anodes. This method generally includes the uniform lead method, hot dip plating and spraying methods, but due to low processing efficiency, thinner coatings, and in use Local anti-corrosion has a short lifespan, so its use is not very common.
4. Standardize the operation to reduce the degree of corrosion
The anti-corrosion of chemical equipment not only needs to start from the materials and anti-corrosion methods, but also pay attention to the normal operation of normal operation to achieve the anti-corrosion effect. In normal work, it is necessary to conduct operation training for workers, improve their safety awareness and standard operation ability, strictly abide by the operation requirements, and prohibit overpressure, overtemperature, and overload operation. In addition, pay attention to daily maintenance and repair, and pay attention to the maintenance of some poorly corrosive and pressure vessels, and make corresponding inspections and records for their preparation materials and construction environment, so that they can operate effectively in daily work. , Improve the anti-corrosion performance of chemical equipment.
