Large Diameter Flange

Large diameter flange usually refers to flanges with a nominal diameter of DN600 or above. It is the core component that connects pipelines and equipment in large pipeline systems (such as municipal engineering and petrochemical plants). With its high strength and large load-bearing capacity, it ensures the safety of high flow medium transportation.

Structure and Type

Large diameter flanges are mostly plate structures, and the thickness of the flange increases with the increase of pressure level (such as DN1000 Class 150 flange thickness of about 30mm, Class 300 up to 50mm). Dozens of bolt holes are distributed at the edge, and high-strength bolts (grade 8.8 and above) are used to tighten with the matching flange. Common types include:

Welding flange: with a long neck design, fully welded to the pipeline, suitable for high-pressure (Class 300 and above) systems, such as the main pipeline of chemical plants;

Sliding sleeve flange: welded outside the pipeline, with low cost, suitable for low-pressure (Class 150) scenarios, such as municipal water supply and drainage pipelines;

Ring connection flange: The sealing surface is trapezoidal groove (RTJ), compatible with metal ring gaskets, resistant to high pressure and high temperature, used for power plant steam pipelines.

Manufacturing process

Due to its large size (with a maximum diameter of DN6000), rolling or forging processes are often used:

Rolled flange: Cut the steel plate and roll it into a circular shape, weld the joint and process the sealing surface, suitable for low-pressure large-diameter (DN2000 or above), with low cost;

Forged flange: The entire steel billet is forged into shape, with dense material and no welding defects. It is used in high-pressure critical systems, but the cost is 2-3 times that of rolled flanges.

After forming, it is necessary to undergo heat treatment to eliminate stress, ensure the flatness of the flange (deviation ≤ 1mm/m), and avoid sealing failure during installation.

Performance and Application

Strong bearing capacity: able to withstand pressures of 1.6-10MPa, suitable for high flow media such as crude oil, natural gas, and industrial wastewater. A single flange can connect pipelines with a diameter of more than 3 meters, with a transport capacity of thousands of cubic meters per hour.

Suitable for complex scenarios: temperature range -40 ℃ to 450 ℃, carbon steel material suitable for room temperature, stainless steel (316L) resistant to seawater corrosion, alloy steel pipe (12Cr1MoV) resistant to high temperature flue gas.

Typical applications include:

Main pipeline connection of municipal sewage treatment plant;

Import and export flanges for large petrochemical storage tanks;

Flanges for oil pipelines on offshore platforms (resistant to wind and wave vibrations).

Precautions

During installation, symmetrical fastening bolts should be used (tightened step by step from the center to both sides) to avoid uneven stress on the flange surface causing leakage; Large diameter flanges require specialized gaskets (such as metal wrapped gaskets with inner rings) to ensure that the sealing surface is fully adhered. Following ASME B16.47 and GB/T 9119 standards, it is an irreplaceable connection hub in large industrial systems.