Characteristics of carbon steel pipes

With the continuous advancement of urbanization, the building materials market is constantly introducing new materials. While many of these materials are commonly encountered in our daily lives, those unfamiliar with the building materials market might not be aware of carbon steel pipes, nor fully understand their advantages and disadvantages, possibly even overlooking their existence. In this article, I'll explain what carbon steel pipes are, along with their benefits and drawbacks.

1) What is Carbon Steel Pipe?

Carbon steel refers to steel whose mechanical properties primarily depend on the carbon content, with minimal alloying elements added. It is sometimes referred to as plain carbon steel or just carbon steel. Specifically, carbon steel is an iron-carbon alloy with a carbon content of less than 2% by weight. Besides carbon, carbon steel typically contains small amounts of silicon, manganese, sulfur, and phosphorus. Generally, as the carbon content increases, the hardness and strength of carbon steel also increase, while its plasticity decreases.

Carbon steel pipes are manufactured from carbon steel ingots or solid round steel that is perforated to create a capillary tube, followed by hot rolling, cold rolling, or cold drawing to produce the final product. These pipes play a crucial role in the steel pipe industry.

2) Advantages and Disadvantages of Carbon Steel Pipes

- Advantages:

Increased Hardness and Wear Resistance: After undergoing heat treatment, carbon steel pipes achieve higher hardness and improved wear resistance.

Moderate Hardness and Good Machinability: In their annealed state, carbon steel pipes exhibit moderate hardness, making them easier to machine.

Abundant Raw Materials and Low Cost: Carbon steel pipes are made from readily available materials, making them cost-effective to produce.

- Disadvantages:

Poor Hot Hardness: The hot hardness of carbon steel pipes is limited, as their hardness and wear resistance significantly decrease when the working temperature exceeds 200 degrees Celsius.

Low Hardenability: Carbon steel has low hardenability. For instance, the diameter of fully hardened steel typically reaches about 15-18 mm with water quenching, whereas non-quenched carbon steel only reaches around 6 mm, making it more prone to deformation and cracking.

3) Classifications of Carbon Steel Materials

- By Application:

Carbon Structural Steel

Carbon Tool Steel

Free-Cutting Structural Steel

- By Smelting Method:

Open Hearth Furnace Steel

Converter Steel

Electric Furnace Steel

- By Deoxidation Method:

Boiling Steel (F)

Killed Steel (Z)

Semi-Killed Steel (b)

Special Killed Steel (TZ)

- By Carbon Content:

Low Carbon Steel

Medium Carbon Steel

High Carbon Steel

- By Sulfur and Phosphorus Content:

Ordinary Carbon Steel (higher sulfur and phosphorus)

High-Quality Carbon Steel (lower sulfur and phosphorus)

High-Grade Steel (very low sulfur and phosphorus)

Ultra-High-Quality Steel

4) Types of Carbon Steel Pipes

Carbon steel pipes can be categorized into various types, including:

Seamless Pipes

Straight Seam Steel Pipes

Spiral Pipes

High-Frequency Welded Steel Pipes

Production Processes:

- Hot-Rolled Seamless Steel Pipe (Extruded):

Process: Round tube billet → Heating → Piercing → Three-roll cross rolling, continuous rolling, or extrusion → Stripping → Sizing (or reducing) → Cooling → Straightening → Hydraulic test (or flaw detection) → Marking → Storage

- Cold-Drawn (Rolled) Carbon Steel Seamless Steel Pipe:

Process: Round tube blank → Heating → Piercing → Heading → Annealing → Pickling → Oiling (copper plating) → Multi-pass cold drawing (cold rolling) → Blank tube → Heat treatment → Straightening → Hydrostatic test (flaw detection) → Marking → Storage

Carbon steel seamless steel pipes are further divided into hot-rolled (extruded) and cold-drawn (rolled) types, with cold-drawn pipes available in both round and special shapes.