Duplex steel flanges, as the name suggests, are produced from raw materials such as duplex steel bars, ingots, or plates, commonly referred to as duplex steel flanges. Flanges, also known as flange plates or flanges, are components that connect pipes to each other. They are connected at the pipe ends. Flanges have holes for bolts, allowing two flanges to be tightly connected. Gaskets are used to seal between the flanges. A flange connection consists of a pair of flanges, a gasket, and several bolts and nuts. The gasket is placed between the sealing surfaces of the two flanges, and after tightening the nuts, the compressive stress on the gasket surface reaches a certain value, causing deformation and filling the uneven areas of the sealing surface, ensuring a tight and leak-proof connection. Some fittings and equipment come with built-in flange plates, which also belong to flange connections. Flange connections are an important method of connecting pipes in construction.
Duplex steel flanges are produced using duplex steel as the raw material. Duplex stainless steel, as the name implies, has approximately equal amounts of ferrite and austenite phases in its solid solution structure, with the content of the minor phase generally needing to reach 30%. With a low carbon content, the chromium content ranges from 18% to 28%, and the nickel content ranges from 3% to 10%. Some steels also contain alloying elements such as molybdenum, copper, niobium, titanium, and nitrogen. This type of steel combines the characteristics of both austenitic and ferritic stainless steels, exhibiting higher plasticity and toughness compared to ferritic stainless steel, no room temperature brittleness, significantly improved intergranular corrosion resistance and weldability, while still maintaining the 475°C brittleness and high thermal conductivity of ferritic stainless steel, as well as superplasticity. Compared to austenitic stainless steel, duplex stainless steel has higher strength and significantly improved intergranular corrosion resistance and resistance to chloride stress corrosion. Duplex stainless steel also has excellent pitting corrosion resistance and is a nickel-saving stainless steel.
Common duplex steel materials produced by flange manufacturers include well-known super duplex steels such as S32205, S31803, S32750, S32760, etc.
Duplex steel S31803, commonly known as F51, has a chemical composition of carbon ≤ 0.030, manganese ≤ 2.00, silicon ≤ 1.00, phosphorus ≤ 0.030, sulfur ≤ 0.020, chromium 21.0~23.0, nickel 4.5~6.5, molybdenum 2.5~3.5, iron balance, and other elements N 0.08~0.2.
The chemical composition of S31803 is quite similar to that of the well-known duplex steel 2205, with little price difference. Therefore, 2205 duplex steel is generally used to replace S31803 duplex steel, but S31803 duplex steel cannot replace 2205 duplex steel. Duplex steel 2205, also known as S32205, commonly referred to as F60, corresponds to the domestic grade: 00Cr22Ni5Mo3N, with a chemical composition of carbon ≤ 0.030, manganese ≤ 2.00, silicon ≤ 1.00, phosphorus ≤ 0.030, sulfur ≤ 0.020, chromium 22.0~23.0, nickel 4.5~6.5, molybdenum 3.0~3.5, iron balance, and other elements N 0.14~0.2.
Duplex steel S32750, also known as 2507, commonly referred to as F53, has a chemical composition of 00Cr25Ni7Mo4N, with carbon ≤ 0.030, manganese ≤ 1.20, silicon ≤ 0.80, phosphorus ≤ 0.035, sulfur 0.020, chromium 24.0~26.0, nickel 6.0~8.0, molybdenum 3.0~5.0, copper ≤ 0.50, iron balance, and other elements N 0.24~0.2.
Duplex steel S32760, commonly known as F55, has the following chemical composition: Carbon ≤0.030, Manganese ≤1.20, Silicon ≤0.80, Phosphorus ≤0.035, Sulfur ≤0.020, Chromium 24.0–26.0, Nickel 6.0–8.0, Molybdenum 3.0–4.0, Copper 0.50–1.0, Iron balance, Others N 0.20–0.30, W 0.50–1.
Duplex steel flanges and expansion joints are suitable for connections on both sides with flanges. During installation, adjust the connection length of the product ends to the flanges, and then uniformly tighten the cover bolts diagonally. After that, adjust the limit nuts to allow the pipeline to expand freely within the range of motion, locking the expansion amount to ensure the safe operation of the pipeline.
In pipelines connected to flanges on both sides, adjust the installation length of the product ends to the flanges during installation. Tighten the cover bolts diagonally and evenly to form a whole with a certain displacement, facilitating adjustments based on site dimensions during installation and maintenance.
High-performance duplex steel flanges can be widely used in various wastewater treatment pipelines, capable of deep-sea operations, seawater desalination, and equipment in the paper industry. They are used as desalination equipment on offshore oil platforms.
Due to these advantages, duplex steel flanges are widely used in various wastewater treatment pipelines, deep-sea operations, seawater desalination, paper industry equipment, food processing equipment, offshore oil platforms (heat exchanger pipes, water treatment, and supply systems), desalination equipment, oilfield pipelines and equipment, and various acidic and alkaline environments. With good wear and corrosion resistance, their service life is four to five years longer than that of ordinary stainless steel. For pipelines in seawater, using duplex steel flanges significantly reduces the cost of product replacement and labor costs, making it relatively cost-effective.