Research on the selection of piping materials in the process of chemical design

The selection of piping materials in the design process of the chemical design stage is very important, which not only affects the quality and safety of chemical products but also affects the production efficiency and the chemical production process, and product quality. Therefore, this paper first analyzes the requirements and principles of piping material selection and then analyzes the key points in detail. To scientifically select the pipeline material, to protect the pipeline from supporting chemical production, and to reduce the safety risks.

The continuous development of chemical production in China has put forward higher requirements for the safety and stability of chemical processes. Chemical design should pay close attention to all aspects of the production system and strictly control safety hazards. Among them, the pipeline is an important structure of chemical production; pipeline material will directly affect chemical production if the choice of pipeline material is not reasonable. It also causes safety accidents, resulting in personal safety and economic losses. Therefore, the research on the reasonable choice of pipeline material has important value, which is conducive to improving the safety of chemical production.

1. Chemical design requirements for the selection of pipeline materials

1.1 Safety requirements

In the chemical design, the choice of pipeline materials should first consider the safety of chemical products to ensure the orderly progress of chemical production to avoid safety accidents caused by pipeline factors, resulting in chemical production stagnation and personnel injury. Therefore, it is necessary to strengthen the safety protection from the pipeline design level and carefully select the pipeline material. Such as, due to an unreasonable choice of pipeline material, corroded by the transport medium, damage to the pipeline occurs, and there is a transport medium leakage, causing safety accidents. In addition, if the pipeline type is unreasonable, the pipe diameter does not match, which can also lead to the risk of media leakage, thus causing safety accidents. On the other hand, if the choice of pipeline material performance cannot meet the requirements, breakage occurs after running for some time, resulting in toxic material media outflow, which will also cause environmental pollution. Therefore, in selecting pipeline materials, it is necessary to strive for safety protection and reliability to improve the safety of chemical production. From a safety point of view, the selection of pipeline material is an inevitable requirement; it must be fully combined with the pipeline production content within the transport medium and the external environment, selecting the appropriate, high-quality pipeline material, applied to chemical production, to ensure the safety of chemical production safe and smooth.

1.2 Economic requirements

In the chemical design, the choice of pipeline materials also needs to consider the economic issues to ensure economic efficiency to avoid the cost of chemical products due to material costs exceeding the budget, increasing the cost of chemical production. We need to consider the cost from different angles to ensure the material is safe and reliable in the material selection. Based on the material, choose a low unit price to establish the economic advantage. Chemical production selection of pipeline materials needs to fully understand the material pipe type, parameters, pipe diameter, and other different performance parameters, and the impact on the cost of the material pipeline. A limited design method should be adopted in material pipe selection, and materials should be selected strictly according to budget and cost targets. The economic assessment should consider the full life cycle horizon and choose material pipe with high long-term economic benefits and avoid choosing material pipe with low short-term economic costs. Considering only short-term economic benefits may increase later pipeline maintenance costs, increasing the capital costs of replacement and repair.

2. Chemical design process in the selection of pipeline materials principles

In chemical production, the pipeline is directly in contact with the production of raw materials and finished products; the quality of its material also affects the product quality. In the production process, to guarantee product quality, it is necessary to make a reasonable choice of pipeline materials to support the work of high quality and high standard of production.
Selecting pipeline materials, first of all, the analysis of the environment, fully investigate the environment in which the pipeline is located, according to the environmental conditions for a reasonable selection of materials, do a good job of material inspection to ensure that the material can meet the design parameters required standards, to ensure that the material can be stable under the corresponding temperature and humidity, will not appear broken or leakage. Secondly, the performance analysis, according to the different chemical production and transportation media, reasonable selection of pipeline materials, according to the special nature of the media reasonable selection of pipeline materials. If the transport medium is flammable and explosive substances, it is necessary to choose low-alloy steel materials as well as carbon steel materials to strengthen safety precautions and strictly control the risk factors. To transport corrosive media, you must choose materials with high corrosion resistance, like pipeline pipes.
In selecting pipeline materials in strict accordance with national regulations and standards to select parameters performance, and pay attention to heat treatment, welding, and other technical parameters to ensure that after welding and other processing, pipe performance can still meet the requirements. Furthermore, temperature changes need to be strictly monitored, and temperature tests can be conducted in advance to ensure that the material can meet the design requirements. According to the temperature characteristics of the transport ring media, choose materials with temperature characteristics to ensure their safe and stable transport media.
Finally, the wall thickness of the pipe should be checked, and the wall thickness of the pipe should also meet the design requirements. Considering the special characteristics of the transport medium and reasonable adjustment of wall thickness, such as transporting corrosive liquids, it is necessary to appropriately increase the thickness of the pipeline to ensure that its corrosion resistance meets the requirements.

3. Chemical design process in the selection of pipeline materials points

3.1 Corrosive media pipeline materials

The pipeline for transporting corrosive media should choose corrosion-resistant materials. Such as the transport of hydrochloric acid can choose steel-lined polypropylene pipeline, polypropylene material corrosion resistance is stable regardless of the pressure, temperature changes will not affect the corrosion resistance, and steel-lined pipe can ensure the strength of the pipe to avoid stress and other factors caused by the rupture of the pipe and lead to corrosive media leakage; transport sulfuric acid should be based on the concentration of sulfuric acid for the choice of pipe material, 98% of concentrated sulfuric acid can choose carbon steel material pipeline. Concentrated sulfuric acid will form a protective film of ferrous sulfate on the surface of the carbon steel material, which can effectively protect the pipeline. However, it should be noted that to protect the protective film and avoid being corroded, the speed of sulfuric acid transportation needs to be controlled and managed; such as the transportation of lye media, there is also a certain degree of corrosiveness, and the problem of pipe cracking often occurs. Therefore, when transporting lye, the concentration and temperature must be strictly controlled to ensure the pipeline gets used safely.

3.2 Low-temperature pipeline materials

Construction of chemical pipeline chemical design process also often involves the use of the construction of low-temperature pipelines; part of the transport medium needs to be stored in a low-temperature environment, and the preservation temperature is -20 ~ -196 ℃, so the pipeline material to have low-temperature resistance. In constructing and designing an anti-low temperature pipeline, not only one material can be used. Different media have different requirements for low temperatures. Suppose the medium transport requirements are -20 ~ -40 ℃, the pipeline construction to avoid the choice of carbon steel materials. If the transport medium requires -40 ~ -70 ℃ temperature, avoid using low-alloy steel materials. If the medium transport requirements are -70 ~ -196 ℃, avoid using alloy steel materials. Different temperature sections have different requirements for pipeline materials, so constructing pipelines should be reasonable in choosing materials. In the low-temperature environment, the performance of carbon steel and low-alloy materials will appear significantly reduced. Therefore, it is necessary to reasonably select pipeline materials according to the pipeline medium to ensure the reasonableness of pipeline construction. Conventional low-alloy and carbon steel materials will appear cold and have a brittle problem under freezing. A reasonable choice of materials is needed when selecting materials. All steel materials used in low-temperature pipelines should be selected from ballast steel materials. In the design of the heat-affected zone, weld metal, base material, and ferritic alloy steel materials, to be in advance, are low-temperature impact tests. In the design of the choice of chromium-nickel austenitic steel materials, if the parameters meet the requirements of -196 ℃, there is no need for a low-temperature impact test. Chromium-nickel austenitic stainless steel weld, if the carbon content of ≥ 0.1%, weld carbon content ≤ 0.1%, and the design temperature is≥ -101 ℃, may not do low-temperature impact test. According to GB/T18984, GB/T14976 standards, ≥ -20 ℃, you can choose 20 steel materials; ≥ -30 ℃, you can choose 10 steel materials; ≥ -40 ℃, you can choose 16Mn steel materials; ≥ -46 ℃, you can choose 16MnDG steel materials; ≥ -196 ℃, you can choose 304H, 347H, 310H and other steel materials. ≥ -253 ℃, you can choose 304, 316L and other steel materials, see Table 1.

Table.1 Low-temperature pipeline material selection recommendations

Design temperature/℃	Material recommendations
≥-20	20# steel
≥-30	10# steel
≥-40	16Mn steel
≥-46	16MnDG steel
≥-196	304H,347H,310H,310S,321H,309S steel
≥-253	304,304H,304L,316L,316H,321,347 steel

3.3 High-temperature piping materials

In addition to low-temperature piping, the chemical plant production process will also use high-temperature materials, the need to build high-temperature piping. In the selection of high-temperature materials, the material yield strength will appear to decrease with the increase in temperature; the yield degree redundancy needs to be considered in advance to ensure that the pipeline can still meet quality standards after the reduced heat yield degree. The plasticity of the material will increase as the temperature rises. Therefore, it is also necessary to select high temperature materials according to the requirements of the medium. As the mechanical properties of the material and the load-bearing properties decrease as the temperature rises, it is more beneficial to extend the life of the pipe. In addition, the corrosion resistance will rise with the temperature; choosing the material with strong corrosion resistance is more conducive to extending the pipe’s life. Heat-resistant pipes should choose pipes with high heat resistance and strong oxygen resistance. In the use of high-temperature steel pipe, which has good heat and oxidation resistance, in the process of plant operation, the surface of the steel pipe forms an oxide film, but the oxide film protection is poor. The oxidation process is fast, forming a protective film on the surface of the steel pipe to slow down the erosion of the steel pipe and improve the oxidation resistance. High-temperature materials, mainly choose high-temperature resistant steel pipe materials in the high-temperature environment, can ensure safe transportation. Still, the material oxidation resistance will directly affect the safety of material transportation. Therefore, in the oxidation environment, carbon steel pipe will form an oxide film on the steel pipe body to cause a threat. To improve the high-temperature pipe oxidation resistance, choose the steel pipe material containing silicon, aluminum, chromium, and other elements. The element chromium oxidizes faster than the element iron, and forming an oxide film on the surface of the pipe will control the continued development of oxidation. The addition of chromium and molybdenum elements of steel pipe materials can improve oxidation resistance and improve the performance of the pipe. Therefore, high-temperature piping materials should use heat-resistant materials and pay more attention to oxidation performance. High-temperature piping is a high-risk pipeline in chemical plants, and the risk is high. Most high-temperature pipelines choose carbon steel materials, whose surface can form an oxide film to improve the pipeline’s safety. Carbon steel materials contain aluminum, silicon, and other elements’ core layer oxide film, which can protect the surface of the pipeline, extend the life of the pipeline and improve the safety of pipeline transportation.

3.4 Gas pipeline materials

Transportation of gas media, the main choice of stainless steel or carbon steel materials. Gas transportation needs to pay attention to the transport temperature and pressure. Such as the transport of oxygen media, the pipeline is required to meet the GB50160 and GBJ16 in the GC2 level, taking into account the powerful combustibility of oxygen; once the leakage occurs during transport, mixed with other gases, there is a high risk of explosive accidents, resulting in personal property damage. Therefore, the transport of oxygen pipeline selected carbon steel or stainless steel materials based on the need to strictly control the pressure and flow rate to the maximum degree to ensure the quality of pipeline construction. In general, if the flow rate is <15m/s, pressure <3MPa, you can choose carbon materials; flow rate <25m/s, pressure <3MPa, you can choose stainless steel materials; flow rate <4.5m/s, pressure >3MPa, you can choose stainless steel materials; flow rate <6m/s, pressure >10MPa, you can choose copper alloy materials.

3.5 Sanitary piping materials

Part of the pharmaceutical chemical or fine chemical plants to produce clean products, special requirements for the selection of materials. To avoid contamination in conveying media, the pipeline material selection of high temperature resistance, corrosion resistance, and smooth materials to ensure non-toxic safety. Generally, choose 316 polished pipes or 304 polished pipes as pipelines. The stainless steel polished pipe according to the finish and the process can be divided into AP, BA, and EP grade three classification situations. In the chemical design, according to the polishing process, tube selection can be.

4. Conclusion

In summary, the chemical design selection of pipeline materials needs to meet the safety and economic requirements in strict accordance with the principles of pipeline material selection. In the selection of pipeline materials, it is necessary to choose from several levels of chemical corrosive media pipeline materials, low temperature pipeline materials, high temperature pipeline materials, gas pipeline materials, and sanitary pipeline materials, according to the characteristics of transport media and requirements of a reasonable choice to ensure that the pipeline materials to meet the transport needs to support the stable production of the chemical industry.
Author: Yu Susu