Processing Technology of Pipe Flanging and Loose Flange Connection Technology

I. Overview of Flanging

A rolled edge (also known as a rolled edge pipe, rolled edge short section, or butt welding ring) is a pipe fitting formed by rolling the end of a pipe outward into a right-angled circular edge. It is used in conjunction with a loose flange to achieve a detachable connection for the pipeline. Rolled edges are commonly used in pipelines made of non-ferrous metals such as stainless steel, copper, and aluminum, as well as in pipeline connection scenarios that require frequent disassembly or where alignment is difficult.

II. Characteristics and Advantages of Flanging

1. Material savings: The flange is made of the same material as the pipe, while the flange can be made of carbon steel, saving precious metal materials;

2. Easy installation: The flange can rotate freely on the pipe, facilitating alignment of the bolt holes;

3. Corrosion resistance: The flange portion in contact with the medium is made of the same material as the pipe, offering good corrosion resistance;

4. Cost-effective: Particularly suitable for large-diameter stainless steel pipes, significantly reducing costs;

5. Highly removable: Suitable for pipelines that require frequent disassembly and maintenance.

III. Classification of Flanging

1. Classification by flange angle:

90-degree flange: Most commonly used, the flange is perpendicular to the pipe;

Flanging from other angles: Customized according to special requirements.

2. Classification by Material:

Stainless steel flange: 304, 304L, 316, 316L, etc.;

Carbon steel flange: 20#, Q235, etc.;

Flanging of non-ferrous metals such as copper and aluminum.

3. Classification by connection type:

Butt-welded flange: connected to the pipe by butt welding;

Overall flanging: Formed by directly flanging the end of the entire pipe.

IV. Processing Technology

1. Cold Flanging Process: At room temperature, the end of the pipe is flanged outward using a flanging die and a press. This process is suitable for small-diameter, thin-walled pipes. Cold flanging does not alter the material structure and results in good surface quality.

2. Hot Flanging Process: The end of the pipe is heated to an appropriate temperature before flanging, making it suitable for large-diameter, thick-walled pipes and high-hardness materials. Hot flanging is easy to form, but the heating temperature must be controlled to prevent overheating.

3. Processing Flow: Cutting → End face machining → Heating (hot flanging) → Flanging forming → Cooling → Bevel machining → Dimensional inspection → Surface treatment.

V. Loose Flange Connection Technology

1. Connection Principle: The loose flange (slip-on flange) is placed on the outside of the spigot end. The flange is not welded to the pipe and can rotate freely. When the bolts are tightened, the flange presses against the end face of the spigot to achieve a seal.

2. Sealing Surface Type: The flange end face serves as the sealing surface, typically in the raised face (RF) configuration, used in conjunction with a gasket.

3. Gasket Selection: Select asbestos rubber gaskets, flexible graphite gaskets, metal wound gaskets, PTFE gaskets, etc., based on the medium, pressure, and temperature.

4. Installation Key Points:

① The flange end face shall be flat, free from cracks and radial scratches;

② The flange bolt holes should be aligned, and the flange can be freely rotated for adjustment;

③ The bolts shall be tightened symmetrically and evenly, with the tightening torque conforming to the specifications;

④ Perform a hydrostatic pressure test and an airtightness test after installation.

VI. Execution Standards

GB/T 12459 "Steel Butt-welding Seamless Pipe Fittings", HG/T 20592 "Steel Pipe Flanges" (loose flange section), ANSI/ASME B16.9 "Factory-Made Wrought Steel Butt-Welding Pipe Fittings", DIN 2673 "Flanged Stubs", JIS B2313, etc.

VII. Application Areas

1. Stainless steel piping systems for petrochemicals;

2. Food and pharmaceutical hygienic piping;

3. Water supply and drainage, and water treatment works;

4. Shipbuilding piping systems;

5. Process piping that requires frequent disassembly for inspection and maintenance.

Cangzhou Kairuifeng Pipeline Equipment Co., Ltd. specializes in the production of various types of pipe flanges and loose flanges, offering a full range of specifications and customization options. We welcome your inquiries and purchases.