Introduction

In pipeline applications, the selection of steel pipe materials needs to take into account the use environment and the service life of the steel pipe. Steel pipes need to comply with industry standards and regulatory requirements.

There are two types of steel pipes in general pipelines: ductile iron pipes and steel pipes.

Ductile Iron Pipe: Characteristics and Advantages

Ductile iron is made by treating molten iron of appropriate composition with pure magnesium before casting. The ductile iron thus formed has high ductility, allowing casting for pipe manufacturing.

Ductile iron pipe production process: Core Making Section – Spinning Section – Heat Treatment Section – Zinc Coating Section – Internal Grinding Section – Hydrostatic Pressure Testing Section – Cement Mortar Lining Section (CML) – Steam Curing Section – Internal Polishing Section – Bituminous Coating Section.

Ductile iron pipes have a service life for more than 100 years due to their strong elasticity, safety and other properties.

Due to its strength and durability, ductile iron pipe can be used as the first pipe fitting to withstand extreme weather conditions.

Ductile iron pipes can be made in larger diameters, making the flow rate and energy efficiency in the pipe higher.

Steel Pipe: Characteristics and Advantages

The main materials of steel pipes are stainless steel, carbon steel and alloy steel. The production process of large diameter above DN600 pipes is mostly rolled and welded steel plates. The small diameter under DN600 is mainly made of hot-rolling.

The high tensile strength and pressure resistance of steel pipes are one of the main reasons for choosing steel pipes. And stainless steel is more corrosive.

The welding of steel pipes is simpler. You only need to weld the corresponding pipe fittings at the groove of the steel pipe. The operation is simple and does not require large tools, and can be operated in any pipe laying space.

Steel pipes are mostly used in oil, natural gas and high-pressure water systems.

Comparing between Ductile Iron Pipe and Steel Pipe

The differences between ductile iron pipes and steel pipes can be made in the following 4 aspects:

Strength and durability

Both ductile iron pipes and steel pipes have excellent strength and durability. The minimum strength requirements for ductile iron are 60,000psi tensile strength, 42,000psi yield strength and 10% minimum elongation.

Corrosion resistance

A reinforced polyethylene shell is wrapped around the ductile iron pipe to help mitigate corrosion. Steel pipes are often coated with different protective materials to prevent rust and corrosion, ensuring their longevity even in harsh conditions.

Installation and handling

Although steel pipes are thicker and heavier, they are also easier to install by machine. Steel pipes can be easily installed with only a small number of personnel and adequate machinery. Ductile iron pipe has push-fit couplings that can be used to reroute pipes, giving installers more site adaptability and flexibility and eliminating the need to draw the line diagrams required for steel pipe installations.

Cost comparison

The initial cost of steel pipes is generally lower than that of ductile iron pipes. However, when long-term costs are considered, ductile iron pipe’s properties such as durability, corrosion resistance and lower maintenance make it a more economical choice over the entire life of the pipe.

Applications of Ductile Iron Pipe and Steel Pipe in Plumbing

Water supply and conveyance: Ductile iron pipes are often used to convey groundwater due to their corrosion resistance and high strength.

Sewer and wastewater systems: Ductile iron pipes are also often used to transport sewer wastewater due to their corrosion resistance and have a longer service life than ordinary steel pipes.

Gas Distribution: Steel pipes are the preferred choice for gas piping systems due to their high strength and resistance to high pressures. Suitable for long-distance transportation of natural gas and other gases.

Fire protection system: Both ductile iron pipes and steel pipes can be used in fire protection systems. Since the pressure and corrosiveness of fire protection pipes are lower than those of oil and natural gas, both types can be used.

Factors to be Considered When Choosing Between Ductile Iron Pipe and Steel Pipe

The following 4 aspects are the investigation directions for selecting steel pipes.

1. Project requirements and specifications: Choose the appropriate pipe according to the oil, natural gas, water, etc. that the project transports.
2. Environmental conditions and soil corrosiveness: According to the project construction environment, choose ductile iron pipes or steel pipes that are resistant to corrosion or high temperature.
3. Budget and long-term cost effectiveness: The initial price cost of steel pipes is lower than that of ductile iron pipes, but ductile iron pipes have a longer service life in corrosive environments. Therefore, ductile iron pipes are more cost-effective in highly corrosive environments.
4. Easy to install and maintain: The push-in joint of ductile iron pipe is more convenient for installation and maintenance.

Conclusion

When selecting cast iron and steel pipes, you need to take into account the specific requirements of the project, such as budget, environmental conditions, pipe functionality, and other factors.

Steel pipes are more suitable for high-pressure, high-strength pipelines. It is common in oil and natural gas transmission pipelines.

Cast iron pipes are suitable for corrosion-resistant, high-strength pipes. It is commonly used in general water supply and sewage pipelines.

In actual projects, only by comprehensively considering the characteristics of materials and project requirements can the best choice be made to ensure the safety and reliability of the pipeline system.

Frequently Asked Questions

1. Which is more durable, ductile iron pipe or steel pipe?

Ductile iron pipe and steel pipe are both known for their durability, but each material has its own set of properties that affect its performance in different applications. The spheroidal graphite structure of ductile iron pipe provides excellent impact resistance and ductility. Steel pipes are used in pipelines that require high strength and resistance to deformation.

2. Can ductile iron pipe and steel pipe be used interchangeably?

Can’t.

Ductile iron pipe and steel pipe are two distinct materials with different properties and characteristics, so they are generally not directly interchangeable in all applications. 

3. How do the costs of ductile iron pipe and steel pipe compare?

Ductile iron pipes tend to be less expensive than steel pipes. However, specific accounting is required when considering many factors such as transportation, installation costs, and service life.

4. Which pipe material is more resistant to corrosion?

• Ductile iron pipes are more corrosion resistant.
• Ductile iron pipes are inherently corrosion-resistant due to their iron-carbon composition, which forms a protective layer on the pipe surface.
• In addition, ductile iron pipes are often lined with materials such as cement mortar, polyethylene or epoxy resin to provide further protection against corrosion.

5. Is ductile iron pipe or steel pipe easier to install and maintain?

• Ductile iron pipes are easier to install and maintain.
• Ductile iron pipe fittings are typically assembled using mechanical joints, push-fit joints, or flange connections, which may require specialized tools and techniques
• Steel pipe connection can be welded, threaded or coupled, providing flexible connection methods based on project requirements and site conditions.