How to connect ductile iron pipes with flanges?

Ductile iron pipes (DI pipes) are widely used in various industries, including water supply, sewage, and industrial piping systems. Connecting these pipes using flanges is a reliable method to ensure a secure and leak-proof system. This article provides a step-by-step guide, essential tools and materials, common challenges, and maintenance tips to help you achieve a robust connection.

Why Choose Flanged Connections for Ductile Iron Pipes?

Flanged connections provide a strong, durable, and easy-to-maintain joint for ductile iron pipes. They allow for easy assembly and disassembly, making them ideal for systems requiring periodic inspection or modification. Flanges also ensure a tight seal when properly installed, reducing the risk of leaks and maintaining system integrity.

Necessary tools and materials for ductile iron pipe and flange connections

To ensure a successful connection, you will need the following tools and materials:
Flanges: Flanges are flat components with bolt holes, designed to connect ductile iron pipes to other system components. They should be made of compatible materials, typically ductile iron, and must meet the required specifications.
Threading Machine: Used to thread the ends of ductile iron pipes for flange attachment. The threading machine must match the pipe's specifications.
Wrenches: Required for tightening bolts and securing the flanges. Ensure you have the correct size to fit the bolts.
Sealants: Leak prevention is critical. Use pipe thread sealants, Teflon tape, or other approved sealing materials for a secure connection.
Corrosion Protection: Apply protective coatings or paints to prevent corrosion and extend the life of the connection.
Gaskets: If required, gaskets are placed between the flanges to enhance sealing and prevent leaks.
Safety Gear: Personal protective equipment such as gloves and safety glasses are essential to ensure safe working conditions.

A Step-by-Step Guide to Connecting Ductile Iron Pipe and Flanges

Follow these steps to connect ductile iron pipes with flanges effectively:

1. Preparation
Begin by collecting all necessary tools and materials. Inspect the ductile iron pipe and flanges for any debris, defects, or irregularities. Clean the surfaces to ensure a smooth installation process.

2. Align the Components
Proper alignment of the pipe and flange is crucial. Misalignment can lead to leaks, pressure loss, or system failure. Use alignment tools or markers to ensure the pipe and flange are correctly positioned.

3. Thread the Pipe
Using a threading machine, cut threads into the end of the ductile iron pipe. Ensure the threads are precise and clean, as damaged or irregular threads can compromise the connection.

4. Attach the Flange
Carefully screw the flange onto the threaded pipe end. Use a wrench to tighten the flange, but avoid over-tightening as this can damage the threads.

5. Insert Bolts and Tighten
Insert bolts through the flange holes, ensuring they pass through both flanges being joined. Tighten the bolts in a crisscross pattern to evenly distribute tension and create a uniform seal.

6. Place Gaskets (If Applicable)
If gaskets are required, position them between the flanges before tightening the bolts. Ensure the gasket is properly seated for optimal sealing performance.

7. Final Inspection
Inspect the connection for any misalignment, loose bolts, or visible gaps. Conduct a pressure test to confirm the connection's integrity and identify potential leaks.

Another step and technology for connecting ductile iron pipes and flanges

With the rapid development of modern society, the demand for ductile iron welded flange pipes in the domestic and foreign markets is increasing rapidly. As a substitute for gray cast iron pipes and other pipes, ductile iron flange pipes are widely used in municipal, industrial and mining enterprises for water supply, gas transmission, oil transmission and other fields due to their excellent corrosion resistance, good ductility, good sealing effect, and easy installation. In the prior art, after the ductile iron pipe and the flange pipe are assembled, they are usually sealed with inner and outer double-pass girth welds. Since there are only two welds, the welding angle is generally 45° during the welding process, and the weld pool is usually only 2mm. The weld is very likely to have problems such as weak weld strength, incomplete weld, and uneven weld, which affects the quality of the ductile iron pipe welded flange pipe.

The flange connection process of ductile iron pipes mainly includes the following steps:

1.Cutting and preparation
First, cut the ductile iron pipe into a specified length according to the project requirements. When cutting, ensure that the cut is flat and perpendicular to the pipeline axis to avoid affecting the subsequent flange installation and welding quality. In addition, the pipe end needs to be cleaned to remove burrs and impurities.

2.Preliminary assembly of flange and pipeline
Heat the flange to above 500℃ so that it can be heat-fitted with the end of the pipeline. This method expands its inner diameter by heating the flange, and fits tightly with the pipeline after cooling to ensure the firmness and sealing of the connection.

3.Implementation of welding process
3.1First welding:
Use shielding gas (such as a mixture of Ar and CO₂) for welding. The welding gun welds the inner and outer gaps of the flange and the pipeline at an angle of 30° to 35° at the same time to form a preliminary inner and outer weld. The welding speed is controlled to complete one circle in 50 to 60 minutes to ensure that the weld is uniform and full.

3.2Secondary welding:
The external weld is welded at least once to enhance the weld strength. The welding speed is controlled within 15 to 25 minutes to complete one circle, and finally a multi-layer weld is formed to improve the welding quality and pressure resistance.

4.Install the gasket and bolt fixation
Place the appropriate gasket between the flanges and tighten the bolts evenly. Use a torque wrench to apply force gradually to ensure that the force on each bolt is uniform to avoid flange deformation and sealing failure.

5.Testing and inspection
After installation, perform pressure test or leak detection on the flange connection to ensure that the sealing and strength of the connection meet the design requirements.

Common Challenges and Solutions

1.Misalignment: Misaligned pipes and flanges can cause leaks or mechanical stress. Use alignment tools to ensure proper positioning.
2.Incorrect Bolt Torque: Over-tightening or under-tightening bolts can lead to leaks or flange damage. Follow the manufacturer's torque specifications.
3.Incompatible Materials: Using materials that are not compatible with ductile iron can result in corrosion or failure. Always select flanges and accessories made of compatible materials.
4.Thread Damage: Damaged threads can weaken the connection. Inspect and clean threads during the preparation phase.

Application scenarios of flange connection

Ductile iron flange pipes are widely used in the following fields:

Municipal engineering: trunk pipelines of urban water supply network and drainage system.

Industrial transportation: gas and liquid transportation pipelines of industrial and mining enterprises.

Fire protection system: connection and adjustment of fire hydrants and pipelines.

Oil and gas transportation: used to transport medium such as oil and natural gas

Conclusion

Connecting ductile iron pipes with flanges is a straightforward yet precise process that requires the right tools, materials, and attention to detail. By following the step-by-step guide provided in this article, you can achieve a secure and durable connection that ensures the efficiency and reliability of your piping system. Regular maintenance and proper installation techniques are key to preventing common issues and extending the lifespan of the connection.

Whether for industrial, municipal, or residential applications, flanged ductile iron pipe connections offer a dependable solution for robust and leak-proof piping systems.