What is a forged flange?

　　In industries such as petrochemicals, gas transmission, and power generation, pipeline systems bear the crucial responsibility of transporting media. Their safe and stable operation is a core element in ensuring production efficiency.

　　As a vital component of pipeline connections, the quality of forged flanges directly impacts the safety and efficiency of the entire system.

　　Definition of Forged Flanges:

       A pipe flange is a disc-shaped pipe connection fitting with bolt holes, typically used in pairs. By aligning the sealing faces of two flanges and tightening them with bolts, nuts, gaskets (for flanges), and washers (for nuts), a reliable sealing structure is formed.

　　Forged flanges are flanges manufactured through a forging process. After heating the metal billet, pressure is applied to the billet through a forging process, causing plastic deformation and thus producing a flange product that meets standard requirements. Its internal structure is dense, with continuous metal flow lines, and its mechanical properties are superior to cast flanges, making it particularly suitable for high-pressure, high-temperature, and corrosive media environments.

　　American Standard Manufacturing System

       The production of American standard forged flanges follows a rigorous standards system. Standards established by the American Standards Institute (ANSI) and the American Society of Mechanical Engineers (ASME) are authoritative and universally applicable worldwide:

　　ASME B16.5: Size standard for pipe flanges and flange fittings, covering sizes from NPS 1/2 to NPS 24 inches, pressure ratings Class 150 to Class 2500 forged steel pipe flanges and flange fittings.

　　ASME B16.47: Standard for large-diameter steel flanges, divided into Series A and Series B, including weld neck flanges and blind flanges with sizes from NPS 26 to NPS 60.

　　ASME B16.36: Specifies the dimensions, tolerances, materials, pressure-temperature ratings, and manufacturing and testing requirements for orifice flanges, applicable to fluid flow measurement connections in industrial pipelines.

　　These standards detail the flange dimensions, tolerances, pressure-temperature ratings, material requirements, test methods, and marking specifications, ensuring product interchangeability and reliability in industrial projects worldwide.

　　Common Material Standards for ASME Pipe Flanges

　　The raw materials for forged flanges are mainly high-quality carbon steel, alloy steel, and stainless steel billets or bars. These materials must meet specific chemical composition and mechanical property requirements. Common ASME standard materials include:

　　Carbon steel: ASTM A105 (for high-temperature environments), ASTM A350 LF2 (for low-temperature environments);

　　Stainless steel: ASTM A182 F304/F304L, F316/F316L, F321, ASTM A182 F51 (duplex stainless steel), etc.;

　　Alloy steel: ASTM A182 F11, F22, F91, etc. (suitable for high-temperature and high-pressure environments);

　　Special alloys: Monel, Inconel, and other corrosion-resistant alloys;

　　The selection of raw materials depends on the corrosiveness, temperature and pressure conditions, and media characteristics of the application environment to ensure the safety performance of the flange throughout its service life.

　　ASME B16.5 Steel Flange Pressure Ratings

　　According to the ASME B16.5 standard, American standard steel flanges are classified into seven pressure ratings: Class 150, 300, 400, 600, 900, 1500, and 2500. The selection of the pressure rating depends on the design pressure, temperature, and medium characteristics of the piping system and is a key parameter to ensure the safe operation of the system.

　　Class 150: Nominal pressure approximately 2.0 MPa, suitable for low-pressure piping systems.

　　Class 300: Nominal pressure approximately 5.0 MPa, commonly used in medium- and low-pressure piping systems, such as some process pipelines in the petrochemical industry and city gas transmission pipelines.

　　Class 600: Nominal pressure approximately 10.0 MPa, suitable for medium- and high-pressure piping systems, such as steam pipelines in the power industry and connection pipelines for high-pressure chemical reactors.

　　Class 900: Nominal pressure approximately 15.0 MPa, mainly used in high-pressure piping systems, such as high-pressure oil pipelines in oil extraction and high-pressure feed pipelines for large chemical equipment.

　　Class 1500: Nominal pressure approximately 25.0 MPa, suitable for piping systems under high pressure and high temperature conditions, such as some piping in nuclear power plants and connection pipes for high-pressure boilers.

　　Class 2500: Nominal pressure approximately 42.0 MPa, belonging to the ultra-high pressure class, mainly used in ultra-high pressure piping systems, such as extraction pipelines in high-pressure oil and gas fields and pipeline connections for special high-pressure experimental equipment.

　　It should be noted that the pressure rating of a flange is not fixed; its actual pressure resistance is affected by factors such as operating temperature and material. In practical applications, it is necessary to select the appropriate flange based on specific operating conditions and relevant standards.

　　Performance Advantages of ASME Standard Steel Flanges

　　Superior Mechanical Properties: The forging process refines the grain size and densifies the metal, effectively reducing internal defects and resulting in forged flanges with higher strength, toughness, and fatigue resistance.

　　Good Sealing Performance: The high precision machining of the sealing surface of forged flanges ensures a smooth surface, forming a tight seal with gaskets and effectively preventing media leakage.

　　Higher Safety and Reliability: The dense and uniform metallographic structure provides excellent pressure resistance and sealing performance. The overall structure is stable and not easily deformed or damaged by external factors.

　　Better Dimensional Accuracy: Forging combined with precision machining allows for strict dimensional tolerances, ensuring precise matching with mating flanges.

　　Wide Material Adaptability: A variety of materials, from carbon steel to special alloys, can be forged to meet different operating conditions.

　　Longer Service Life: Excellent corrosion resistance and creep resistance, low maintenance costs, and high overall economic benefits.

　　Advanced Manufacturing Process

　　The production of modern forged flanges integrates traditional forging techniques with advanced manufacturing technologies:

　　Raw Material Inspection: Based on the flange's design requirements and application industry, suitable metal raw materials are selected. Strict chemical composition analysis, mechanical property testing, and visual inspection are conducted on the steel billets to ensure material quality.

　　Heating: The heating temperature must be precisely controlled according to the material of the raw material and the forging process requirements. During the heating process, attention must be paid to controlling the heating rate and holding time to prevent defects such as overheating or burning of the raw material.

　　Forging and Shaping: Free forging or die forging processes are used, with a press or forging hammer to plastically deform the metal into its initial shape. During the forging process, the forging force, number of forging passes, and forging temperature must be reasonably controlled according to the flange's size and shape requirements to ensure the dimensional accuracy and mechanical properties of the forging.

　　Heat Treatment: The main function is to eliminate internal stress generated during forging and improve the microstructure and mechanical properties of the forging. Heat treatment processes mainly include annealing, normalizing, quenching, and tempering. The specific heat treatment process needs to be determined based on the flange's material and performance requirements.

　　Machining: Precision machining of flange faces, beveling, bolt holes, etc., using CNC machine tools.

　　Surface Treatment: Surface anti-corrosion treatment as required, including rust-preventive oil, painting, galvanizing, PTFE anti-corrosion treatment, etc.

　　Quality Inspection: Including dimensional inspection, hardness testing, impact testing, non-destructive testing (UT, MT, PT, etc.), and pressure testing.

　　Final Inspection and Marking: Product identification and quality documentation preparation according to standard requirements.

　　Applications of Flanges:

　　Oil & Gas Industry: Connection systems for oil and gas pipelines and extraction equipment subjected to high pressure and high temperature.

　　Chemical Industry: Pipeline connections for acid and alkali media and chemical reaction equipment requiring corrosion resistance.

　　Power Energy Industry: High-temperature and high-pressure steam pipelines for thermal power, nuclear power, and renewable energy power plants.

　　Shipbuilding: Critical connection components for marine propulsion systems, pipeline networks, and offshore platforms.

　　Water Treatment Industry: Reliable connection assurance for large-scale water supply and drainage systems and seawater desalination plants.

　　Pharmaceutical & Food Industry: Sanitary stainless steel flanges to meet clean and aseptic production requirements.

　　Paper Industry: Corrosion-resistant flanges to withstand the harsh environments of chemical pulping and bleaching processes.

　　Aerospace: Special alloy flanges to meet extreme temperature and lightweight design requirements.

　　Mining & Metallurgy: Durable connection solutions for heavy equipment and high-wear environments.