Black Steel Pipe Vs Carbon Steel Pipe

What is Carbon Steel Pipe?

Carbon steel pipe is the most common type of steel pipe. It is made from ingots or solid round steel, perforated into a rough tube, and then hot-rolled, cold-rolled, or cold-drawn. It can be categorized as seamless carbon steel pipe, straight-seam, and spiral carbon steel pipe.

Carbon steel is a type of steel with a high carbon content, an alloy of iron and carbon. It is divided into three categories: high-carbon steel, medium-carbon steel, and low-carbon steel. The mass fraction of carbon ranges from 0.05% to 2.5%. Carbon steel pipe is known for its hardness and durability.

What is Black Steel Pipe?

Black steel pipe is uncoated steel pipe. Its dark color comes from iron oxide formed on its surface during the manufacturing process. During forging, a black oxide layer forms on the surface, giving this type of pipe its smooth finish.

Black steel pipe is commonly made from low-carbon steel plate or billet. The main processes used to manufacture it are seamless black steel pipe and welded black steel pipe. Seamless black steel pipe is made directly from hot-rolled or cold-drawn seamless pipe. Welded black steel pipe is made by welding steel sheets from rolled sheets and then heat-treating them.

Black steel pipe is inexpensive and versatile. It can transport a variety of media, such as oil, natural gas, waste, and sludge.

The Difference Between Carbon Steel and Black Steel

Composition Differences

Carbon steel pipe is primarily composed of iron and carbon (typically 0.05% to 2.0%), with trace elements such as phosphorus, sulfur, silicon, and manganese.

Compositionally, black steel pipe is not significantly different from carbon steel pipe. In fact, black steel pipe is carbon steel pipe that has undergone a special treatment process. Its primary components are iron and carbon, but it is not galvanized or coated, but instead has an iron oxide layer.

Manufacturing Differences

Carbon steel pipe can be categorized as seamless (produced by hot rolling or cold drawing) or welded (straight seam welded or spiral welded).

Black steel pipe is manufactured using a similar process to carbon steel pipe and can be categorized as seamless or welded, but it always remains uncoated.

Differences in Temperature and Pressure Resistance

Black steel pipe comes in a variety of grades, with performance tailored to specific temperature and pressure ratings. Key factors to consider are generally the steel grade, gauge, and thickness. Carbon steel pipe can withstand temperatures up to 650°C and is often used for high-pressure fluid transport (e.g., ASTM A106 high-temperature pipe).

Like carbon steel pipe, black steel pipe also offers excellent resistance to high temperatures and pressures, as its composition enables it to withstand high temperatures. However, black steel pipe is more commonly used in medium- and low-pressure fluids and structural applications.

Corrosion Resistance Differences

Carbon steel pipe is susceptible to rust if not galvanized or otherwise treated for corrosion, as carbon steel does not contain chromium. However, corrosion resistance can be improved through galvanizing, lining, or coating.

Black steel pipe lacks a galvanized coating on the exterior, making it susceptible to corrosion damage. For optimal performance, it should be used indoors. While black steel pipe is a popular choice for oil and gas transportation, it is not recommended for domestic water supply.

Appearance Differences

Carbon steel pipe has a rough, matte, and dull metallic surface. Oxidation can lead to a rusty finish.

Black steel pipe has a dark, rough surface to the touch, due to a layer of iron oxide.

Cost Differences

Because of the wide variety of carbon steel pipe grades, prices vary widely. Mild steel pipe is inexpensive, while high-carbon steel pipe is more expensive. For example, ASTM A36 mild steel pipe is significantly less expensive than ASTM AISI 1059 pipe.

Black steel pipe is simple to manufacture and affordable. It's well-suited for a variety of transportation and structural applications, being economical, weldable, and versatile.

Application Differences

Carbon steel pipe is most commonly used in structural applications such as buildings and bridges.

Black steel pipe is seamless, making it commonly used to transport fluids such as water, natural gas, and oil.

Environmental Differences

Steel is inherently a relatively environmentally friendly material. This makes black steel more environmentally friendly and sustainable, as the blackening process simply adds a hardening layer of iron oxide to the surface, while carbon steel must be carburized, which releases more carbon dioxide into the atmosphere than the blackening process.

If environmental considerations are a concern, black steel pipe is the best choice. If you need stronger steel to withstand significant structural loads or similar load-bearing tasks, carbon steel pipe is almost always the best choice.

Conclusion

Carbon steel pipe is versatile, while black steel pipe offers a combination of strength and cost-effectiveness. Carbon steel pipe and black steel pipe are the industry's mainstays. Choosing between them depends on your needs. For example, if you're designing an indoor plumbing system, you'd likely prefer corrosion-resistant mild steel pipe. In structural applications, black steel pipe can be used as beams and scaffolding, providing a sturdy solution.