Large‑diameter flanges (typically those with diameters reaching or exceeding 600 mm) are critical connecting components for transporting high‑pressure, high‑flow‑rate media in petrochemical, power generation, and offshore engineering. These flanges must withstand enormous internal pressures while ensuring long‑term stable sealing performance. Their manufacturing, machining, transport, and installation present special challenges not encountered with ordinary flanges.
In terms of manufacturing and machining, the primary difficulties for large‑diameter flanges are controlling material defects and preventing machining deformation. For example, a flange with a diameter of two metres requires a 200‑tonne steel ingot for forging, imposing extremely stringent requirements on internal ingot quality—inclusion sizes must be controlled within a very narrow limit. For such large forgings, the uniformity of metal flow during forging and the densification of internal structure are difficult to guarantee, requiring advanced forging processes and rigorous process control.
The heat treatment stage is another technical challenge in large‑diameter flange manufacturing. During heat treatment, if the temperature difference between different regions of the flange face is too large, severe warping deformation can occur. In practice, segmented heating processes are used to control temperature uniformity, placing high demands on heating equipment performance and operational precision.
In terms of forming processes, large‑diameter flanges also present a dilemma. Open‑die forming can achieve larger diameters, but the flange thickness is often less than the pipe wall thickness; closed‑die forming can achieve greater thickness, but the flange diameter is limited. To obtain flanges with both large diameter and sufficient thickness, the industry has developed innovative processes such as multi‑step upsetting.
For some ultra‑large flanges, because the billet cannot be forged as a single piece, manufacturers have to adopt segmented forging—the flange is divided into several segments, each forged separately, then assembled by welding. Post‑weld tempering is required to eliminate residual welding stresses, followed by final machining. Although this segmented manufacturing approach overcomes forging equipment limitations, it imposes higher requirements on welding procedures and quality control.
In transport and installation, large‑diameter flanges also face many difficulties. A single large flange can weigh several tens of tonnes, requiring specially designed tooling to prevent deformation during lifting and transport. On‑site assembly demands extremely high precision in bolt‑hole alignment—errors must be controlled within a very small range, often using precision measuring equipment such as laser alignment instruments.
The manufacturing of large‑diameter flanges epitomises the technical sophistication of the flange industry. Process control at every step directly affects the final product quality and operational safety.
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