Chemical pressure vessel corrosion effective control strategy research
With the continuous improvement of China’s industrialization level, pressure vessels are widely used in chemical production. Pressure, temperature, media and humidity and other factors can lead to pressure vessels in the use of the process of more serious corrosion problems. Because of the corrosion of a variety of situations, this paper from the strengthening of the pressure vessel corrosion phenomenon to start research, and targeted to different corrosion situations to put forward the corresponding protective measures.
Pressure vessel is a closed container, can carry a certain pressure, can be loaded with gas or liquid. In the use cycle of the pressure vessel, do a good job of maintenance work, increase the frequency and strength of maintenance, in order to ensure that the pressure vessel can be put into normal industrial production.
The principle of corrosion of chemical machinery and equipment
Chemical machinery and equipment in the actual operation will be affected by the industrial atmosphere, resulting in equipment corrosion problems. Industrial areas are prone to pollution, in urban planning and construction, often set industrial areas in the city center far away from the location, and concentrated placement of factories. Industrial pollution causes more serious damage to the atmosphere, industrial gases contain more harmful substances, such as sulfur dioxide, carbon dioxide, nitrogen dioxide, etc., these gases are easy to fuse with the acid in the atmosphere, thus producing acid rain. Chemical equipment in this environment for a long time, the metal material on the surface of the equipment will be corroded by acidic substances, oxidation and reduction reactions, eventually leading to more serious corrosion phenomenon.
Pressure vessel corrosion types and causes
Some of the chemical materials stored inside the pressure vessel is not a long-term static state, but constantly reacting, under the influence of stirring and other forces, will continue to rotate and tumble and flow, a variety of chemical substances in the process of movement mixed and mixed with each other, and even the formation of viscous state of raw materials, in the continuous reaction movement will inevitably scour the inner wall of the pressure vessel. In the process of reaction, either sticky pull or squeeze, can be collectively referred to as the stress effect. This corrosion phenomenon of corrosion is very rapid, and it is difficult to be found, the corrosion caused by the vessel is also more serious.
Wet corrosion is often called electrochemical corrosion, sometimes also known as reactive corrosion, the formation of the reason is in the interior of the pressure vessel, carrying the electrolytic solute and the solvent wall electrochemical reaction, the interior of the pressure vessel caused by damage and corrosion.
Corrosion. This corrosion phenomenon is more common in the operation of chemical pressure vessels. In the electrochemical reaction process, the anions and cations will gather in different areas, thus creating a potential difference, and then the formation of anionic and cathodic ionic current, the overall structure of the metal atoms in the pressure vessel is simultaneously destroyed, and electrochemical reactions occur at the anode and cathode. The anodic reaction is the pressure vessel’s internal metal lost electrons into the electrolyte solution after the oxidation reaction; cathodic reaction is the oxidizer gained the pressure vessel metal surface solution of electrons generated by the reduction reaction. Electrochemical corrosion phenomenon generally does not occur alone, often accompanied by mechanical, biological, physical and other reactions, prolonged electrochemical corrosion will cause serious damage to the pressure vessel.
Physical corrosion is generally known as dissolution corrosion, the formation of the cause is the pressure vessel in the long storage of liquid raw materials to produce physical dissolution phenomenon, this phenomenon and electrochemical reaction has a different nature. In the process of physical corrosion, the metal and the structure of the solution will not undergo any form of change and chemical reaction, but simply the physical dissolution. Pressure vessel is at room temperature and pressure environment, in addition to a few chemical properties of the more active metals, other metals generally do not react with each other. Once the pressure vessel is in a high temperature and pressure environment, the low melting point of the metal will be converted into a liquid state, the high melting point of the metal will remain as a solid state, the liquid metal will dissolve the solid metal, but also corrode the internal metal of the pressure vessel. For example, liquid zinc will corrode the iron and steel elements in the metal container. In the process of metal dissolution, iron and steel elements will change in form, will be stripped from the inner wall of the pressure vessel, dissolved in the liquid zinc, resulting in the thinning of the inner wall of the metal vessel, resulting in corrosion phenomena.
Dry corrosion phenomenon is also known as chemical corrosion. The formation of dry corrosion phenomenon is the environment of non-electrolyte solution and dry gas contact, in the interior of the pressure vessel a series of chemical reactions, including synthesis, reduction, decomposition, oxidation and replacement reactions, etc.. The atoms contained in the metal are reassembled and rearranged, resulting in new substances, often precipitates, and the reaction will be hot and glowing and discolored, and the material of the pressure vessel is changed during the reaction.
In the reaction process, the pressure vessel material suffered a change, reducing the pressure vessel high temperature and high pressure resistance performance. The main way to distinguish between dry corrosion and physical corrosion is to observe whether new substances are produced in the reaction process. The difference between dry corrosion and wet corrosion is mainly between the metal atoms and the oxidizer although the exchange of electrons, but in the process of the reaction will not produce current.
Petrochemical equipment corrosion phenomenon belongs to uniform corrosion, is the chemical pressure vessel surface corrosion phenomenon occurs as a whole, but this corrosion phenomenon for the normal operation of the machine will not have a significant impact, will only cause changes to the appearance of machinery. In the manufacturing process of machinery, the design of good corrosion margin will be able to control the occurrence of uniform corrosion, to ensure that the normal operation of machinery. Measure the amount of uniform corrosion is the standard in the unit of time, the corrosion medium on the material caused by the depth of corrosion or the degree of weakening of the metal wall.
To prevent the occurrence of pressure vessel corrosion recommendations
Selection of suitable materials
Pressure vessels should be based on the actual use and in the operation of the process of temperature, pressure and media to design. In the process of making pressure vessels, choose the right main material, try to process a variety of materials to form a wear-resistant alloy, or add some gold-containing elements to the metal material to form stainless steel, which can greatly enhance the corrosion resistance of the pressure vessel and slow down the speed of the pressure vessel material being corroded.
In the selection of pressure vessel manufacturing materials, to fully consider the flammability, corrosion and toxicity of the medium. To a certain extent, reduce the use of materials that can chemically react with the medium. For some electrolytes and high temperature media, to avoid iron as the main material to make pressure vessels.
Scientific use of corrosion inhibitors
Corrosion inhibitors can significantly reduce the corrosion effect. Slow corrosion reagent is generally composed of a variety of chemical substances. Scientific selection of corrosion inhibitors, not only can significantly shorten the degree of corrosion of the pressure vessel, but also can increase the service life of the pressure vessel, and can ensure the safe use of pressure vessels in the subsequent work. It is worth noting that the corrosion inhibitor is not the more the better, once the corrosion inhibitor is used in excess, it will intensify the corrosion of the pressure vessel, but also affect the formation of the purity of chemical raw materials. To use corrosion inhibitors according to the type of raw materials to reasonable, and strictly in accordance with a reasonable amount of use.
Ice brine anti-corrosion technology
Ice brine corrosion protection technology refers to the addition of frozen brine retardant in the pressure vessel, this means of corrosion protection is more economical and convenient, is a commonly used anti-corrosion measures. In general the preservative is sodium dichromate containing sodium hydroxide. When adding the preservative, to ensure that the brine is weakly alkaline, the pH value is strictly controlled at 8.5, which can be measured using phenolphthalein reagent, while the brine can also be frozen with mechanical filtration to reduce the impurities in it.
Metal protection layer technology
Metal protective layer refers to the formation of a special coating on the inner wall of the pressure vessel, mainly using some difficult to be corroded metal materials, the use of electroplating or spraying the form of its attachment to the metal surface, mainly including zinc, chromium, nickel and so on. Generally
The general use of spray plating method and uniform lead plating method for the pressure vessel configuration of the protective layer. At present, the more widely used way is metal thermal spraying, this technology is easy to operate, only the use of spray guns can be sprayed directly, will not cause harm to the operator, the process requirements are simple, the degree of pollution of the environment is small, the cost is also relatively low.
In summary, the chemical pressure vessel in the process of operation, often affected by a variety of factors, in the internal corrosion phenomenon is more serious, will not only reduce the service life of the container, but also the quality of chemical raw materials will have a significant impact, and even delay the schedule. Therefore, master the chemical pressure vessel in the corrosion phenomenon of the causes and laws, to find out the chemical pressure vessel in the process of operation will appear to influence the factors, take targeted means to prevent the corrosion of chemical pressure vessels, in order to ensure the service life of chemical equipment and engineering quality.
Source: Network Arrangement – China Pressure Vessels Manufacturer – www.secmachinery.com
www.secmachinery.com is one of the leading china filtration equipment & sanitary stainless steel pressure vessels manufacturer, with professional factory. We focus on the sanitary pressure vessels, filtration equipment research and development, manufacturing, sales and service since the company been established. Our products is widely used on bio-pharmaceutical, food and beverage, fine chemical industry.
If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]