Manufacturing Process of Carbon Steel Flange Fittings
Publication Date:
Jul 30,2026
Author:
Dacheng Jiaye
Carbon steel flange pipe fittings remain the most widely used connection accessories in general industrial pipelines due to balanced cost and mechanical performance. The mainstream manufacturing routes include forging, casting and plate cutting, among which forged flanges occupy dominant positions for pressure-bearing pipeline applications.
Carbon steel flange pipe fittings remain the most widely used connection accessories in general industrial pipelines due to balanced cost and mechanical performance. The mainstream manufacturing routes include forging, casting and plate cutting, among which forged flanges occupy dominant positions for pressure-bearing pipeline applications. Forged carbon steel flange production starts with raw material inspection. Manufacturers test chemical composition and mechanical properties of carbon steel round bars to eliminate unqualified raw materials. Next step is heating treatment. Steel blanks are heated to specified temperature ranges inside heating furnaces to improve plasticity and reduce forming resistance. Hot forging follows heating, utilizing hydraulic forging presses or air hammers to deform steel blanks into rough flange shapes. Forging processes refine internal metal grain structures, eliminate internal material pores and cracks, greatly enhancing tensile strength and pressure bearing capacity compared with casting workpieces. After rough forging, rough flanges enter machining procedures. CNC lathes process flange outer circles, inner holes, sealing surfaces and bolt holes according to standard dimensional drawings. Precision control of sealing surface flatness and roughness is critical, as surface defects will destroy subsequent sealing effects. After machining, heat treatment procedures such as normalizing or tempering are carried out to release internal stress generated during forging and machining. Stress relief prevents flange deformation after long-term installation and usage. Subsequent surface treatment includes rust removal, anti-rust oil coating or black oxide treatment to avoid oxidation corrosion during storage and transportation. Cast carbon steel flanges are manufactured via casting molds. Molten carbon steel is poured into molds for forming. Casting technology can produce complex special-shaped flanges, yet internal defects such as shrinkage cavities and sand holes are hard to avoid. Therefore cast flanges are generally limited to low-pressure non-critical pipeline systems. Plate cutting flanges are directly cut from carbon steel plates. This process has low production costs and short delivery cycles, suitable for small-batch simple flat flanges with low pressure requirements. Every finished carbon steel flange needs strict quality inspection, including dimensional detection, visual surface inspection, magnetic particle testing for surface cracks and ultrasonic testing for internal defects. Qualified products will be marked with material grade, pressure class, standard code and production batch number for traceability.
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