Basic Process for Large Elbows
18 Sep,2025
The basic manufacturing process for large-radius bends involves first welding a multi-faceted ring shell with a polygonal cross-section—or a multi-faceted sector shell closed at both ends. Once the interior is completely filled with a pressurized medium, internal pressure is applied. Under this pressure, the polygonal cross-section gradually transforms into a circular shape, forming a seamless, round ring shell. Depending on requirements, this circular ring shell can then be cut into four 90-degree bends, six 60-degree bends, or other customized bend specifications. This process is ideal for producing large-radius bends of any size where the ratio of the bend’s centerline diameter to its inner diameter exceeds 1.5—and it currently stands as the preferred method for manufacturing high-pressure, large-diameter bends.
The advantages are primarily evident in the following areas:
(1) It eliminates the need for a pipe billet as a raw material, reducing costs associated with pipe-making equipment and molds, while also enabling the production of bends with virtually any diameter and relatively thin wall thickness.
(2) The workpiece is either a flat plate or a developable curved surface, making material cutting simple, precision easy to achieve, and assembly-welding convenient.
(3) Due to these two reasons, the manufacturing cycle can be shortened, significantly reducing production costs. Additionally, since no specialized equipment is required, this technology is particularly well-suited for on-site fabrication of large-diameter bends. This innovative technique has already been submitted for a national invention patent.
Technical indicators
This technology is suitable for manufacturing any bend with a working pressure below 10 MPa, an inner diameter \( d \) of 125 mm, and a ratio \( D/d \) between the bend's centerline diameter \( D \) and its inner diameter \( d \) of at least 1.5—though there’s no upper limit on the size of the bend's centerline diameter. For instance, it can be used to process large bends with an inner diameter of 12 meters and a centerline diameter exceeding 60 meters.
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