Forming standards and production process of hot-pressed elbows

Hot-Compression Elbow Forming Standards and Production Process

1. Hot-Compression Elbow Forming Standards

Hot-Compression Elbows, as a commonly used pipe fitting, are widely used in industries such as petroleum, natural gas, chemicals, power generation, construction, and shipbuilding. To ensure safety and reliability, the following standards must generally be met:

Manufacturing Standards

National Standards (GB/T 12459, GB/T 13401)

Ministry of Chemical Industry Standards (SH3408, SH3409)

Electric Power Industry Standards (DL/T 695)

Petroleum Standards (SY/T 0510)

International Standards: ASME B16.9, DIN 2605, JIS B2313, etc.

Material Standards

Carbon Steel: 20#, Q235, Q345, etc.

Alloy Steel: 16Mn, 12Cr1MoV, 10CrMo910, etc.

Stainless Steel: 304, 316, 321, 904L, etc.

Forming and Dimensional Tolerance Requirements

The bending radius (R) is generally specified as 1D, 1.5D, or 2.5D of the pipe diameter (D).

Ovality, wall thickness deviation, and joint clearance must comply with relevant standards. The surface quality should be free of defects such as cracks, folds, and slag inclusions.

II. Production Process of Hot-pressed Elbows

Hot-pressed elbows primarily utilize heating, molding, and cooling processes. The basic flow is as follows:

Cutting

Cut straight pipe sections of appropriate length based on the angle and dimensions of the elbow.

Cutting accuracy directly impacts the subsequent forming process.

Heating

Heat the cut pipe sections to 800°C–1000°C to achieve a plastic state.

A medium-frequency induction furnace or gas-fired furnace is typically used.

Mold Forming (Hot-pressing or Pressing)

Pressing: The heated pipe section is placed in a forming mold and extruded into the elbow shape using a press or hydraulic press.

Pushing: Using a dedicated pushing machine, pressure is gradually applied between a mandrel and an outer mold, forcing the pipe material along the mold into the elbow.

During the forming process, the metal stretches along the inner and outer arcs, and the wall thickness may thin or thicken, which requires control. Cooling and Straightening

After forming, allow natural or controlled cooling to avoid cracks and stress concentration.

Use shaping dies or mechanical straightening equipment to ensure the angle and roundness of the elbow.

Heat Treatment

For alloy steel elbows or elbows with higher requirements, normalizing, annealing, or quenching and tempering are required to improve the microstructure and mechanical properties.

Machining and Finishing

Machine the ends to ensure the end face is flat and the bevel angle meets welding requirements.

Inspect wall thickness, bend angle, and dimensional deviation.

Inspection

Appearance Inspection: The surface must be free of defects such as cracks, folds, and pores.

Dimensional Inspection: Angles, wall thickness, roundness, and ovality must meet standards.

Nondestructive Testing: Radiographic and ultrasonic testing are performed to ensure the absence of internal defects.

If necessary, perform a hydrostatic or pneumatic test to ensure pressure resistance.

Surface Treatment and Protection

Carbon steel elbows generally require sandblasting to remove rust and then apply anti-rust paint.

Stainless steel elbows can be pickled and passivated to improve corrosion resistance. Advantages of Hot-Pressed Elbows

Suitable for the production of large-diameter, thick-walled elbows.

Uniform molding, dense microstructure, and excellent mechanical properties.

Suitable for mass production with high efficiency.

Our products are suitable for high-temperature, high-pressure, and corrosive working conditions.

Cangzhou Aosendic Pipe Fittings Manufacturing Co., Ltd. is a large-scale manufacturer specializing in the production of elbows, tees, reducers, elbows, and caps. We comply with ASTM, ANSI, JIS, DIN, GB, and other standards, covering virtually all types of steel.

Please contact us for any purchasing needs or questions.

Mobile: 86-13668807131

Website: https://www.authenticfitting.com/

Address: Mengcun Hui Autonomous County, Cangzhou City, Hebei Province

Email: authentic013@steelpipes-fitting.com