How Pipe Flanges Are Made: A Step-by-Step Look at Flange Manufacturing
- Fulihua
- 1 day ago
- 3 min read
When you bolt a flange onto a pipeline, you are trusting a piece of metal to hold pressure, resist corrosion, and maintain a leak-free seal — sometimes at thousands of PSI, in extreme temperatures, for decades. But how exactly is that flange made? Here is a step-by-step look at the manufacturing process behind a precision pipe flange.
Step 1: Raw Material Selection and Cutting
Every flange begins as a certified steel billet or plate. At Fulihua, we source raw materials with full mill test reports (MTRs) verifying chemical composition and mechanical properties. The material is then cut to the required blank size based on the target flange dimensions and pressure class.
Common materials include carbon steel (ASTM A105), stainless steel (ASTM A182 F304/F316), and duplex stainless steel (2205/2507) for corrosive service environments. Material selection is determined by the operating medium, temperature, and applicable project standard.
Step 2: Heating and Forging
The cut billet is heated to the appropriate forging temperature — typically between 1,100°C and 1,250°C for carbon steel — and then pressed or hammered into a rough flange shape using hydraulic forging equipment. Forging aligns the grain structure of the steel, producing a denser, stronger part compared to casting. This is why forged flanges are the preferred choice for high-pressure and safety-critical applications.
Step 3: Normalizing / Heat Treatment
After forging, the blank undergoes heat treatment — typically normalizing or quench-and-temper — to relieve internal stresses introduced during the forging process and to achieve the required mechanical properties specified by the material standard.
Step 4: CNC Turning and Facing
This is where raw forgings become precision components. As shown in the image above, the flange blank is mounted on a CNC lathe and machined to exact dimensional tolerances. The bore, outer diameter, thickness, and raised face (or other facing type) are all turned to specification. Surface finish on the sealing face is critical — ASME B16.5 specifies a specific serrated finish measured in microinches to ensure proper gasket seating.
Step 5: CNC Drilling
Bolt holes are drilled using a CNC high-speed drilling center to ensure precise pitch circle diameter (PCD), hole size, and angular spacing. Incorrect bolt hole positioning is one of the most common causes of flange misalignment on site, so this step demands tight process control.
Step 6: Inspection and Testing
Before any flange leaves the facility, it goes through dimensional inspection against the applicable standard (ASME B16.5, B16.47, EN 1092, etc.), visual surface inspection, and material verification via spectrometer (PMI). Where specified, additional tests such as hydrostatic testing, ultrasonic examination, or magnetic particle inspection are conducted.
Step 7: Marking, Coating, and Packaging
Finished flanges are marked with material grade, heat number, pressure class, size, and standard reference in accordance with the applicable specification. A rust-preventive coating is applied to machined surfaces, and flanges are packaged with protective end covers to prevent damage during transit.
Why Manufacturing Process Matters When Choosing a Supplier
Not all flanges are manufactured to the same standard. A flange that looks identical on the outside may have been cast rather than forged, made from non-certified material, or machined to loose tolerances. When qualifying a supplier, always request mill test reports, dimensional inspection records, and information about their production equipment and quality control process.
At Fulihua Pipeline Equipment, every flange we produce is fully traceable from raw material to finished product, with documentation available for customer review. Our production facility operates CNC machining centers and high-speed drilling equipment, and our quality team performs in-process checks at every stage.
Contact us at sales@flhmetal.com to request product specifications, samples, or a competitive quotation.
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