Forged steel flanges are among the most widely used components in industrial piping systems. Thanks to their high mechanical strength, excellent pressure and temperature resistance, forged flanges are ideal for demanding applications in oil & gas, chemical processing, power generation, and water treatment.
In this article, Sunjin Metals Vina (SJM Vina) provides a detailed look into the manufacturing process of forged steel flanges—from raw material selection to machining and final quality checks—to help customers better understand the technical value behind each flange.
1. Raw Material Selection
The most common raw materials for forged flanges include:
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Carbon steel: ASTM A105, SS400, S20C
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Alloy steel: A182 F11, F22
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Stainless steel: SUS304, SUS316, A182 F304, F316
Flange blanks are typically round bars or pre-cast billets, selected based on the target flange size and pressure class.
Example:
To manufacture a 4-inch ANSI Class 300 welding neck flange, a forged round bar with a diameter of 160–180 mm made from A105 carbon steel is typically used.
2. Primary Forging
At this stage, the steel billet is heated to 1100–1250°C, then shaped using compressive force to form the basic flange profile.
There are two main forging methods:
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Open-die forging: A power hammer strikes the billet freely—suitable for large sizes or custom orders.
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Closed-die forging: The heated billet is compressed within a mold—ideal for mass production with uniform dimensions and tighter tolerances.
After forging, the flange blank is cooled naturally or further heat treated depending on technical requirements.
3. Heat Treatment (if required)
To achieve the desired mechanical properties, forged flanges may undergo additional heat treatments such as:
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Annealing: Reduces internal stress and improves machinability
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Quenching and tempering: Increases hardness and tensile strength
Heat treatment is essential when required by the applicable standard or material specification.
4. Precision Machining
After forging, the semi-finished flange is transferred to CNC or conventional lathes for detailed finishing:
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Facing the sealing surface (Raised Face, Flat Face, or RTJ)
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Turning the bore and outside diameter
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Drilling bolt holes and chamfering edges
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Cutting grooves for gaskets if applicable
Example:
A DIN 2633 DN80 flange requires 8 bolt holes with a PCD of 160 mm. These are precisely drilled using multi-head drill machines to ensure uniform spacing and alignment.
5. Quality Inspection (QC)
Every flange must pass rigorous inspection before leaving the factory:
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Dimensional check: Diameter, thickness, bolt pattern, and PCD
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Surface inspection: Ensure no cracks, blowholes, or visible defects
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Material testing: Verify chemical composition and mechanical properties via Mill Test Certificate (MTC)
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Non-destructive testing (NDT): Ultrasonic, magnetic particle, or dye penetrant tests if required
Only flanges that meet all specifications are approved, stamped, and released for packaging.
6. Surface Treatment and Packaging
Depending on the intended application, flanges may undergo:
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Shot blasting to clean the surface
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Rust-preventive coating or black paint for carbon steel
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Pickling and passivation for stainless steel
The finished flanges are then wrapped in plastic film, packed in cartons or wooden cases, and labeled with full technical information and documentation (CO, CQ, drawings, MTC, etc.).
Sunjin Metals Vina – Trusted Supplier of Forged Steel Flanges
With years of experience in industrial piping materials, Sunjin Metals Vina (SJM Vina) proudly supplies high-quality forged steel flanges to customers across Vietnam and beyond:
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Standards: JIS, ANSI, DIN
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Types: Welding Neck, Slip-on, Blind, Threaded Flanges
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Materials: A105, SS400, Stainless Steel 304/316, Alloy Steel
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Sizes available from DN15 to DN600
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Full documentation: CO, CQ, Mill Test Certificate
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Fast delivery, technical consultation included
Address: 628 Le Hong Phong, Ward 10, District 10, Ho Chi Minh City, Vietnam
Hotline: +84 33 4233 127
Email: sjmvina@sunjinmetal.com
Website: www.sjmvina.com.vn
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