In the process of chemical design, the corrosion resistance of the materials, not being flammable and explosive, and being high-temperature resistant to reduce the probability of accidents must be taken into account when selecting materials for chemical pipelines. In the chemical design, the parameters of pipeline materials must be clarified. There are relatively high requirements on the working parameters of the medium in China. According to the medium parameters, the material selection of
pipes should be reasonable, and the pipeline parameters should be adjusted reasonably according to the actual situation of pipelines. In addition, when selecting the pipeline's material, we should consider the mechanical, chemical, and physical properties.
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Principles for choosing materials for pipelines
First, the inspection steps, heat treatment steps, welding steps, and design content must be optimized to achieve the relevant regulations. Second, the principle of the selection of piping materials should be paid attention to. There are differences between media materials and other materials, so the safe transportation must be guaranteed. Third, it is necessary to ensure that the design principles of the material meet the requirements for the transportation of special substances. For different media, the selected pipe material must be consistent with them. For example, During transportation, if the transported material is corrosive, the corrosion range of the material must be considered. The anti-corrosion intervention must be strengthened, and the anti-corrosion effect can be enhanced to meet the temperature requirements in the transportation process. Temperature shock testing should be performed to make materials comply with design standards.
Choosing pipeline materials in the chemical design process
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Selecting low-temperature materials
In the process of designing chemical pipelines, low-temperature conditions occur occasionally. When engineering construction is carried out at low temperatures, the temperature is mostly below -20°C. It is necessary to ensure that the construction of chemical pipelines has good low-temperature resistance. Therefore, in the process of designing chemical pipelines, materials must be selected reasonably according to temperature conditions. There are differences in the requirements for construction materials in different low-temperature environments. If the temperature is between -20°C and -40°C, carbon steel cannot be selected in the pipeline's design process. If the temperature is between -40°C and-70°C, low-alloy steel cannot be selected. If the temperature is from -70°C to -196°C, alloys cannot be selected. Under different temperature ranges, there are different requirements for the temperature of the pipe material. In the process of pipeline construction, the ambient temperature must be reasonably controlled. As the performance of carbon steel pipes and low-alloy pipes decreases significantly under low temperatures, it is impossible to realize the material functions under normal temperatures. Moreover, The damage probability of the pipeline increases under low-temperature environments. If you want to ensure the performance of pipeline materials, you must rationally choose low-temperature piping materials.
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Materials for high-temperature pipes
The manufacturing process of some chemical products is at high temperatures. Because the pipeline must transport high-temperature products, it is necessary to ensure that the materials are high-temperature resistant. In the process of designing chemical pipelines, materials must be selected from the following aspects. Under different temperature conditions, the pipeline materials are different, and the yield strength of the pipeline also has a certain difference. The plastic shape will show a proportional change, and the yield strength an inverse proportional change. With the extension of the transporting time, the mechanical properties and load strength of the pipe material will also change accordingly. Under different temperature conditions, the tensile strength of the pipe material will also change to different degrees. Temperature changes will cause corrosion to pipeline materials to varying degrees. In chemical production, once the temperature exceeds 350°C, it can be regarded as a high-temperature environment. High-temperature materials have high-temperature limits. Taking carbon steel as an example, once the temperature is above 425°C, it will be graphitized, and alloying elements must be added to the carbon steel to reduce the occurrence of graphitization and ensure its stable performance. In addition, killed steel or killed steel containing aluminum can be used for pipeline design to promote the improvement of the pipeline’s safety performance.
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Materials for plastic lining
In the production process of chemical products, the temperature tolerance of the lining material must be below the service temperature of the lining pipe. In the selection process of the lining material, polypropylene and PTFE must be used as the main materials. The designer should choose the plastic lining based on the characteristics of the production environment, and materials cannot be used in different environments.
If the medium transported by the pipeline is sulfuric acid, ensure that the pipeline's material can adapt to the chemical properties of sulfuric acid. Analyze the chemical properties of sulfuric acid with different concentrations; understand the difference in properties, and reasonably select sulfuric acid. If ordinary carbon steel pipes are selected, the stable rate of transporting concentrated sulfuric acid must be ensured to make sure the stable performance of the concentrated sulfuric acid temperature value in the process of conveying concentrated sulfuric acid by carbon steel pipes, ensuring the stable flow rate of sulfuric acid, and reducing the different speed of sulfuric acid or too fast flow rate. Concentrated sulfuric acid can be effectively stored in iron containers without corroding iron containers. The main reason is that after concentrated sulfuric acid is in contact with iron containers, it can form high-density ferroferric oxide film on the surface of iron containers. The ferroferric oxide film isolates the corrosive effect of concentrated sulfuric acid on carbon steel pipes. If the flow rate of concentrated sulfuric acid is uneven or the flow rate is too fast, it will cause the temperature value of the concentrated sulfuric acid to change. Once the temperature increases, the oxide film will be affected and destroyed. The protective effect of the iron will decrease, and increase corrosion of the pipeline. If chemical conditions cannot control the flow rate of concentrated sulfuric acid, you can use stainless steel pipes to ensure that the internal pressure of the pipe is below 2.5MPa and the temperature is controlled below 30℃ to maintain the stability of the chemical and physical properties of the stainless steel pipe and to ensure the safe and stable transportation of concentrated sulfuric acid.
(5) Materials for hydrochloric acid
The corrosiveness of hydrochloric acid is still relatively great. In order to reasonably choose pipes transporting hydrochloric acid, the application of hydrochloric acid must be analyzed. If the concentration of hydrochloric acid is within 15% to 30%, non-metallic materials can be used for transporting hydrochloric acid. Non-metallic materials have a good anti-hydrochloric acid corrosion effect, and can maintain good corrosion resistance and a reasonable temperature. In addition, if the hydrochloric acid environment is complicated, the effect of applying non-metallic materials is also very significant. For example, pipe made from polypropylene has insufficient introduction efficiency and good thermal insulation performance. Polypropylene pipes have better melting joint strength. The disconnection of the pipe can be effectively reduced. The pipes made from polypropylene have a relatively small density value, light weight, convenient application, and long service life. Moreover, using polypropylene for pipes has low costs and can be used more. It's just that there are certain defects in the process of transporting hydrochloric acid. For example, when it suddenly rains or snows heavily, the performance of the pipe will be greatly reduced. If the construction is carried out under bad weather conditions, it is recommended to use plastic lining materials or other types of non-metallic materials for construction.