Types of corrosion in the petrochemical industry and anti-corrosion measures related to measuring instruments

In the industrial production of the petrochemical industry, the corrosion of various acidic and alkaline raw materials and other substances on production equipment is a common phenomenon. The existence of corrosion phenomena will undoubtedly have an adverse effect on the working life of the equipment and the stability of production. For example, the production efficiency can be improved by improving the production process and the automation level of the equipment, while improving the stable operation of the equipment and effectively enhancing the avoidance of potential dangers. This article is aimed at the analysis and discussion of the common anti-corrosion problems in the petrochemical industry, introducing the corrosion types of commonly used instruments, and proposing different anti-corrosion measures according to different corrosion types. Through the application of a series of anti-corrosion measures, the damage to the equipment caused by corrosion can be greatly reduced, and at the same time, the workload of operators and maintenance personnel can be reduced, the maintenance funds invested by the enterprise can be reduced, the production efficiency of the enterprise can be improved, and considerable economic benefits can be brought to the enterprise.
 
       The anti-corrosion problem of chemical instruments is an issue that cannot be bypassed. After the efforts of professional researchers from various scientific research institutes and enterprise engineers, many corrosion-resistant materials have been developed and put into practical use, including metal materials, non-metallic materials and alloy materials. These materials play an important role in the anti-corrosion protection of measuring instruments in production activities.
 
1. Types of corrosion of chemical instruments
Before introducing various anti-corrosion methods, we first introduce the concepts and different types of corrosion that exist in chemical production.　　
　　Corrosion refers to the physical and chemical reactions between metals and moisture and gas in the external environment, which causes changes in the surface and internal properties of metals, resulting in damage to the functional structure of metal materials or other components. In the petrochemical industry, chemical instruments and their components are prone to physical, chemical and electrochemical reactions with the external contact environment, causing damage to chemical instruments and their components. Transmitters are often used as front-end acquisition and detection devices in industrial sites. Transmitter petroleum sensors are composed of loose pieces and connecting wires. These components are made of precious metals to improve the detection accuracy and sensitivity of the equipment. These devices are exposed to the harsh environment of industrial sites, causing corrosion. Common types of corrosion include:
　　1. Physical corrosion
　　The damage of metal materials by external mechanical forces and the physical dissolution of metal materials will cause physical corrosion of chemical instruments.
　　2. Chemical corrosion
　　The metal materials of instruments are prone to oxidation-reduction reactions with gases in the external contact environment, and non-electrolyte solutions contact metal materials to produce oxidative corrosion, which are all chemical corrosion of chemical instruments. The toxic gas chlorine produced by the chemical plant and the iron element in the instrument components undergo an oxidation-reduction reaction to generate ferrous chloride, causing instrument corrosion.
　　3. Electrochemical corrosion
　　The most common corrosion in chemical instruments is electrochemical corrosion. In the chemical environment, there are common corrosive substances such as strong acids and strong alkalis. When the metal materials of chemical instruments come into contact with the electrolyte solution, the galvanic cell reaction principle occurs, and the active metal materials with strong reduction lose electrons and are oxidized. Steel materials are more susceptible to corrosion in humid air because the steel surface reacts in humid air to generate electrolytes, and the electrolyte solution forms a galvanic cell device with the iron and carbon in the steel, and the iron element loses electrons and is oxidized. Many metal materials are damaged by electrochemical corrosion. Electrochemical corrosion corrodes the surface and internal parts of the instrument in a short period of time, and the sediment caused by corrosion will affect the precision and accuracy of the instrument.
　　
2. Instrument anti-corrosion method
       With the existence of corrosion problems, anti-corrosion problems arise. In production, corrosion and anti-corrosion are like a pair of give and take.
In the petrochemical industry, a large amount of corrosive substances are generated in the production process of enterprises. The detection instruments used in the process are seriously corroded, which greatly reduces the service life of the instrument. In the actual production process, the existence of corrosion causes frequent instrument failures. Enterprises frequently replace instruments to ensure the normal operation of production equipment, thereby increasing the operating and maintenance costs of enterprises. The widely used anti-corrosion methods in the chemical industry include: isolation method, anti-corrosion material method, development of anti-corrosion sensors, installation of corrosion-resistant valves, etc. Among them, the isolation method is the most commonly used. For example, when using an anti-corrosion electromagnetic flowmeter to measure acidic and alkaline media, the isolation materials used are polytetrafluoroethylene and PP.
　　1. Gas isolation
　　The principle of gas isolation is to fill the pressure pipe between the detection point and the instrument detection element with air to prevent the detected pressure medium from directly contacting the instrument and protect the instrument from being damaged by the high-pressure measured medium. The gas isolation method is also called the gas injection protection method, which is used when using a pressure transmitter to measure low pressure or absolute pressure. The pressure change at the detection point is sensed by the air in the pressure pipe to the instrument transmitter, and the result is obtained by the instrument sensitive element.
　　2. Liquid isolation
　　When measuring hydrogen chloride, nitrogen oxide, chlorine and other media, perfluorotributylamine or other isolation liquids are filled in the isolation tank to isolate the corrosive medium from the metal parts of the detection instrument. There are some disadvantages in the liquid isolation method. For example, adding a liquid seal will cause a liquid seal medium, and the measured medium may react chemically with the liquid seal medium, thereby causing new corrosion problems and reducing the isolation effect. At the same time, the isolation liquid on the market is generally expensive, the filling method is troublesome, and the anti-corrosion effect is not good. In practical applications, the liquid isolation method is not widely used.
　　3. Diaphragm isolation
　　Due to the characteristics of high lubricity, high and low temperature resistance, weather aging resistance, corrosion resistance, non-adhesion, low tension, and low friction coefficient of polytetrafluoroethylene, it is resistant to most chemical solvents and drugs. Therefore, the anti-corrosion isolation diaphragm of chemical instruments is composed of polytetrafluoroethylene. The specific application method is to use polytetrafluoroethylene propylene or polytetrafluoroethylene diaphragm to adhere or spray on the bellows of the pressure transmitter or the spring tube of the pressure gauge, so that the corrosive medium and the sensor element are isolated to achieve the purpose of anti-corrosion. Applications have shown that the FEP diaphragm can prevent corrosion from common corrosive media, ensure the accuracy of instrument measurement during the measurement process, and greatly extend the service life of the detection instrument. In addition, the FEP diaphragm is relatively cheap, and the method of using diaphragm isolation for anti-corrosion can solve the corrosion problem on the one hand, and reduce production costs on the other.
　　
III. Conclusion of this article
　　The corrosion problem of chemical instruments is one of the difficult problems that chemical companies urgently need to solve. To solve this problem, scientific and technological personnel need to continuously research and develop, improve the anti-corrosion ability of chemical instruments, strengthen isolation and anti-corrosion ability, and develop more anti-corrosion methods. At the same time, capital investment and long-term production practice are also indispensable. The suggestions put forward in this article hope to help chemical companies better solve the corrosion problem of Beigong instruments