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Piping design is a complex process that requires considering various factors to ensure the safety, reliability, and cost-effectiveness of the piping system. The following are some of the main design considerations: 1. Economic diameter – The choice of diameter affects the economic efficiency of the installation. Pipeline investment accounts for a significant portion of the total installation cost, around 10%-20%. An increase in diameter raises costs related to pipe walls, valves, fittings, insulation materials, etc. While increasing the flow rate can reduce the required diameter, it also increases frictional resistance, leading to higher energy consumption and operational costs. Therefore, it is necessary to find the optimal balance point to determine the most economical diameter. Currently, the pipe diameter is initially selected based on the recommended flow rate range and pressure drop values for pipe length, and the calculation results are relatively close to the economically optimal diameter. 2. The pressure drop requirement specifies that the pressure drop in the pipeline should be calculated with the valve fully open; this pressure drop must be below the allowable value, otherwise the flow rate will not meet the process requirements. Pipes that allow for a smaller pressure drop can use a lower flow rate, while those with a larger pressure drop can use a higher flow rate ； When calculating the pipe diameter, if the allowable pressure drop is the same, pipes with different diameters should use different flow velocities: lower flow velocities for smaller diameters, and higher flow velocities for larger diameters ； For fluids with high viscosity, a large pressure drop results in a low flow rate, while those with low viscosity allow for a higher flow rate. 3. Process control requirements: To achieve good flow control, the pressure drop across the control valve generally accounts for about 30% of the total pressure drop in the control system; for systems with stable flow, this value can be 20%. An excessively low pressure drop of the control valve can make flow control difficult. 4. Limiting wall wear: The metal protective film provides corrosion resistance; however, an excessively high flow rate of the medium inside the pipe can damage this protective film, leading to erosion and wear of the pipe and thus reducing its service life. Conditions such as corrosive media, soft-metal pipes, media containing abrasive solid particles, and highly turbulent pipes can accelerate the corrosion rate of pipes; therefore, the flow velocity should be limited, with a recommended maximum flow velocity for liquids of 2 m/s. 5. To meet the requirements for the safe transportation of the medium, the flow rate of the medium must comply with the relevant **standards. Process engineers need to consult the relevant regulations or documents to obtain reliable data; in the absence of such data, they can calculate the flow rate based on existing production facilities as a reference. 6. Meeting noise control requirements: Pipeline systems generate noise under conditions such as high flow rates, throttling, cavitation, and turbulence. Reducing the flow rate can lower noise levels, while an increase in flow rate leads to a significant rise in noise. For pipelines with strict noise restrictions, it is possible to increase the pipe diameter in order to reduce the flow rate. Flow rates should be even lower in sections where the cross-section and flow direction change abruptly. However, in gas transportation, noise is increased due to friction between particles and the pipe walls, and this is not governed by ordinary flow rate limitations. 7. In accordance with the standards for pipe materials, there are differences in the series of outer diameters and wall thicknesses for metric and imperial pipes; it is necessary to determine the wall thickness first before making calculations. The outer diameters of pipes with common nominal diameters can be found in the relevant tables. 8. Execution standards (for reference only) 1) Scope of application and pipeline classification: In accordance with GB/T 20801 \"Code for Pressure Piping – Industrial Piping\", the design of industrial metal pressure pipelines must meet specific requirements regarding scope of application and pipeline classification. 2) Design and calculation: The design and calculation of pressure pipelines shall comply with the provisions of GB/T 20801.3, including the determination of parameters such as pipeline dimensions, pressure, and temperature. 3) Material selection: The construction materials for pressure pipelines shall comply with the requirements of GB/T 20801.2 to ensure the materials’ pressure resistance, corrosion resistance, and temperature resistance. 4) Fabrication and installation: The fabrication and installation of pressure pipelines shall comply with the provisions of GB/T 20801.4, including welding, flange connection, threaded connection, etc. 5) Inspection and testing: The inspection and testing of pressure pipelines shall comply with the provisions of GB/T 20801.5 to ensure the safety performance of the pipeline system. 6) Safety protection: The safety protection for pressure pipelines shall comply with the provisions of GB/T 20801.6, including anti-static measures and anti-aging measures. 7) Pipe diameter restrictions: It shall comply with the provisions of the \"Design Specifications for Pipeline Materials in Chemical Plant Equipment (HG/T 20646.2)\".