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Selecting the type of elbow suitable for a particular application scenario requires comprehensive consideration of media characteristics, pressure and temperature, installation space, fluid resistance, cost budget and many other factors. The following are specific selection points and recommendations:
First, according to the media characteristics of choice
1. Corrosive media
Material priority: need to choose corrosion-resistant stainless steel (such as 316L, 317L), to avoid corrosion caused by ordinary 304 material leakage.
Structural requirements: If the medium is extremely corrosive, the priority selection of the whole pressed elbow (no weld), to reduce the risk of corrosion of welded joints; if you have to use welded elbows, you need to ensure that the weld is pickled passivation or cladding corrosion-resistant alloy treatment.
2. High-temperature media (such as steam, hot oil)
Material selection: selection of high-temperature resistant materials (such as 321, 310S), to avoid the decline in strength of ordinary materials at high temperatures.
Bending radius: Priority selection of long radius elbow, reduce the vortex and pressure loss when the media flow, while reducing the pipeline stress concentration at high temperatures (long radius elbow stress distribution is more uniform).
3. high viscosity or particulate media (such as mud, slurry)
Inner wall requirements: choose the smooth inner wall of the pushed elbow to reduce media retention and wear; avoid the use of pressed elbows (there may be a problem of the inner wall is not smooth).
Wear protection: If the medium is highly abrasive, use thick-walled elbows or composite elbows lined with wear-resistant materials (such as ceramics).
Second, according to the pressure and temperature selection
1. High-pressure systems (such as chemical pipelines, natural gas pipelines)
Structural strength: must choose seamless pressed elbow or forged elbow to ensure overall strength; avoid the use of welded elbows (weld seam may become a weak point under high pressure).
Bending radius: Priority selection of long radius elbow (R = 1.5D), to reduce the stress concentration at the bend, to prevent cracking under high pressure.
2. low-pressure systems (such as drainage, ventilation pipes)
Cost priority: short radius elbow (R = 1D) or welded elbow can be selected to reduce costs and installation space occupation.
Special scenarios: If the low-pressure system is sensitive to noise (such as building drainage), the long radius elbow can reduce the noise of water impact.
Third, according to the installation space selection
1. Sufficient space for the scene (such as outdoor piping, industrial plants)
Priority selection of long radius elbow to ensure smooth flow of fluids, reduce resistance and energy consumption. 2.
2. Space-constrained scenes (such as construction pipe shafts, ship's cabin)
Choose short radius elbow or customized angle elbow (such as 60 °, 30 °), to save space; but need to pay attention:
If the medium is liquid or gas, you need to check whether the fluid resistance is within the allowable range (short radius elbow resistance is about 30% to 50% higher than the long radius).
If used for high-pressure or high-temperature system, the need for stress analysis of the elbow, if necessary, to increase the support or the use of reinforced elbow.
Fourth, according to the fluid resistance requirements to choose
1. Strictly limit the resistance of the system (such as precision chemical, aerospace piping)
Must use a long radius elbow, or even a large radius elbow (R ≥ 3D) or oval elbow to minimize fluid disturbance and pressure loss.
2. allow a certain resistance to the system (such as general water supply and drainage, ventilation)
Short radius elbows can be used, especially in the case of cost or space priority.
V. Other key factors
1. Cost budget
Price ranking: forged elbow > seamless pressed elbow > pushed elbow > welded elbow; long radius elbow > short radius elbow.
Cost-effective considerations: low-pressure, room temperature, non-corrosive scenarios, the lowest cost of welded short radius elbow; high-pressure, corrosive scenarios, give priority to the reliable performance of the seamless pressed long radius elbow, to avoid the cost of maintenance in the later stages.
2. Installation and maintenance
Welding requirements: welded elbows need to ensure that the welder's qualifications and weld testing (such as radiation flaw detection), to avoid leakage; threaded elbows (small diameter) need to pay attention to the compatibility of sealing materials (such as PTFE raw material tape).
Maintenance convenience: If the elbow requires frequent maintenance, flange connection elbow can be used to facilitate disassembly; buried pipeline is preferred to choose welding or heat fusion connection elbow to ensure sealing.
3. Industry standards and norms
Different industries have specific requirements, for example:
Petrochemical: follow ASME B16.9, GB/T 12459 and other standards, high-pressure piping must use long radius seamless elbow.
Building water supply and drainage: GB/T 19228.1 and other standards, allowing the use of short radius welded elbow.
Food and medicine: sanitary elbow (inner wall polished, Ra ≤ 0.8μm), the material is mostly 316L, the connection method is preferred to clamp or automatic welding butt.