ASTM A234 WPB-S Return Bend For Power Plants and Steam Boilers

ASTM A234 WPB-S Return Bend Composition

ASTM A234 WPB-S Return Bend Strength Characteristics​

1. Mechanical Strength​

• Tensile Strength: The minimum tensile strength of ASTM A234 WPB-S Return Bend is 415 MPa. This high tensile strength enables it to withstand the pulling forces generated in the pipeline system during operation, preventing the fitting from being pulled apart.​ Yield Strength: Its minimum yield strength is 240 MPa.
• Yield strength is an important indicator of the material's ability to resist plastic deformation. With this yield strength, the fitting can maintain its original shape and performance under normal working pressure without permanent deformation.​
• Impact Toughness: It has good impact toughness, especially at low temperatures. When tested at -29°C, the impact energy is usually not less than 27 J. This ensures that the fitting can resist sudden impact loads in cold environments, such as in cold regions or during the transportation of low-temperature fluids, without brittle fracture.​

2. Pressure and Temperature Resistance​

• Pressure Resistance: It is suitable for medium and high - pressure pipeline systems. The maximum allowable working pressure (MAWP) varies with the nominal size and wall thickness of the fitting. For example, for a 2 - inch nominal size and Schedule 40 wall thickness, the MAWP can reach up to 1.6 MPa at room temperature, and it can still maintain a certain pressure - bearing capacity at higher temperatures.​
• Temperature Resistance: It can operate in a wide temperature range, generally from -29°C to 427°C. Within this temperature range, its mechanical properties remain stable, and there is no significant degradation in strength and toughness. This makes it applicable to pipeline systems that transport high - temperature fluids such as steam and hot oil, as well as low - temperature fluid transportation scenarios.​

ASTM A234 WPB-S Return Bend Making Process​

1. Raw Material Selection and Inspection​

• Raw Material: High - quality carbon steel seamless pipes that meet the requirements of ASTM A234 WPB grade are selected as the raw materials. The chemical composition of the carbon steel must comply with the standard, with carbon content ranging from 0.25% to 0.35%, manganese content from 0.80% to 1.20%, and small amounts of elements such as silicon, phosphorus, and sulfur (phosphorus content ≤0.035%, sulfur content ≤0.035%) to ensure the material's performance.​
• Inspection: The raw materials undergo strict chemical composition analysis (using methods such as spectral analysis) and mechanical property testing (including tensile testing and impact testing) to ensure that they meet the ASTM A234 WPB grade standards. In addition, the appearance and dimensional accuracy of the seamless pipes are inspected to avoid using pipes with surface defects (such as cracks, scratches) or dimensional deviations.​

2. Forming Process​

Hot Push Forming: This is the main forming method for ASTM A234 WPB-S Return Bend. First, the seamless pipe is cut into sections of the required length. Then, the pipe section is heated to a certain temperature (usually 800 - 950°C) in a heating furnace to make it have good plasticity. Next, using a special hot push machine, the heated pipe section is pushed through a mold with a U - shaped cavity. Under the action of external force, the pipe section is gradually formed into the shape of a Return Bend. During the forming process, the temperature and pushing speed are strictly controlled to ensure the uniform wall thickness and accurate shape of the fitting.​

3. Heat Treatment​ Normalization Treatment: After forming, the Return Bend needs to undergo normalization treatment. It is heated to a temperature above the Ac3 phase transition point (usually 890 - 950°C) and held for a certain period of time (depending on the thickness of the fitting, generally 1 - 2 hours) to make the internal structure of the material uniform. Then, it is cooled in air to obtain a fine pearlite + ferrite structure. This treatment can improve the mechanical properties of the fitting, enhance its strength and toughness, and eliminate the internal stress generated during the forming process.​

4. Machining and Finishing​

• End Machining: The two ends of the Return Bend are machined to meet the required dimensional accuracy and surface roughness. Common machining methods include turning and threading (if threaded connections are required). The end face must be perpendicular to the axis of the fitting to ensure a good seal when connecting with pipes.​
• Surface Treatment: The surface of the fitting is treated to prevent corrosion. Common surface treatment methods include pickling and passivation, which can remove the oxide scale and rust on the surface and form a protective film. For pipeline systems in harsh environments, additional anti - corrosion treatments such as galvanizing or painting can be carried out.​

5. Quality Inspection​

• Dimensional Inspection: The outer diameter, inner diameter, wall thickness, bend radius, and length of the Return Bend are measured using precision measuring tools such as calipers, micrometers, and coordinate measuring machines to ensure they comply with the design and standard requirements.​
• Non - Destructive Testing: Non - destructive testing methods such as ultrasonic testing (UT) and radiographic testing (RT) are used to inspect the internal and surface quality of the fitting. Ultrasonic testing can detect internal defects such as cracks and inclusions, while radiographic testing can clearly show the internal structure of the fitting to ensure there are no hidden defects.​
• Pressure Testing: A hydrostatic pressure test is conducted on the Return Bend. The fitting is filled with water and pressurized to 1.5 times the maximum allowable working pressure, and held for a certain period of time (usually 10 - 30 minutes). During the test, there should be no leakage, deformation, or other abnormal phenomena, indicating that the fitting has good pressure - bearing capacity and sealing performance.​

ASTM A234 WPB-S Return Bend Application Fields​

1. Petroleum and Natural Gas Industry​ In oil and gas exploration and production, ASTM A234 WPB-S Return Bend is widely used in wellhead pipelines, gathering and transportation pipelines, and oil and gas processing plants. It is used to change the direction of oil, gas, and other fluids in the pipeline system, such as in the return pipeline of the wellhead and the pipeline connection of the separator. Its high pressure resistance and temperature resistance can adapt to the harsh working conditions of high pressure and high temperature in the oil and gas industry.​
2. Chemical Industry​ In chemical plants, it is used in various chemical process pipelines, such as pipelines for transporting acids, alkalis, solvents, and other chemical media. The corrosion - resistant surface treatment and stable mechanical properties of the fitting ensure that it can safely transport various chemical media without being corroded or damaged, ensuring the normal operation of the chemical production process. For example, in the production of fertilizers, it is used in the pipeline system of ammonia synthesis and urea production.​
3. Power Industry​ In thermal power plants and nuclear power plants (except for special high - radiation areas), ASTM A234 WPB-S Return Bend is used in steam pipelines, feedwater pipelines, and condensate pipelines. It can withstand the high temperature and high pressure of steam (up to 427°C and several MPa) and ensure the smooth circulation of steam and water in the power system. For example, in the steam turbine system of a thermal power plant, it is used to connect the steam inlet and outlet pipelines of the turbine.​
4. Water Treatment Industry​ In urban water supply and drainage systems, industrial wastewater treatment systems, and desalination plants, it is used in pipeline systems for transporting water, sewage, and desalinated water. Its good corrosion resistance (after appropriate surface treatment) can prevent the fitting from being corroded by water and impurities in the water, ensuring the unobstructed transportation of water and the normal operation of the water treatment system. For example, in the reverse osmosis desalination process, it is used in the pipeline connection of the reverse osmosis membrane module.​
5. Heating and Air - Conditioning Systems​ In central heating systems and central air - conditioning water systems, it is used in pipeline systems for transporting hot water or cold water. It can change the direction of the water flow in the pipeline to adapt to the layout of the heating or air - conditioning equipment. Its stable performance ensures the efficient transmission of heat or cold energy, improving the heating or cooling effect of the system.​