Black Iron Pipe vs. Black Steel Pipe

Black iron pipe is a common term in the construction industry for welded steel pipes, while black steel pipe is a broader industrial term encompassing various types of uncoated carbon steel pipes.

Black Iron Pipe vs. Black Steel Pipe Differences:

1. Definition Difference

Black Iron Pipe: 

Black iron pipe is a common name for ordinary welded steel pipes. The word "iron" retains historical usage (actually referring to low-carbon steel). It is primarily made of straight-seam electric resistance welded pipe (ERW) and has a lower cost.

Manufacturing Process: It is made by rolling and welding steel plates or strips, therefore, there is a weld seam on the pipe wall.

Surface Characteristics: "Black" refers to the black iron oxide scale on its surface. It has not undergone galvanizing or other anti-corrosion treatment and appears black or gray.

Applications: Black iron pipes are also called water and gas pipes. They mainly conform to standards such as ASTM A53 and are used for low-pressure fluid transportation (water, gas, heating). They are most commonly used in construction sites and plumbing.

Black Steel Pipe: 

Black steel pipe refers to various black steel pipes in their raw state without any anti-corrosion coating (such as galvanizing or chrome plating). The word "steel" clearly defines its material. It can be a pipe or a structural component, thus contrasting with "galvanized iron pipe" (i.e., gi pipe).

2. Material and Standard Differences

Black Iron Pipe: Typically uses low-carbon steel (such as Q235 or ASTM A53 Grade A/B). The material is relatively soft, easy to cut and thread. Standards mainly follow the fluid-use sections of ASTM A53 (American standard) or GB/T 3091 (Chinese standard).

Black Steel Pipe: Offers a wide range of materials, from ordinary carbon steel to high-quality carbon steel and even low-alloy steel. Besides standards for fluid transportation, it also follows various standards such as structural pipes (e.g., ASTM A500), boiler tubes (e.g., ASTM A106), and line pipes (e.g., API 5L). Seamless black steel pipes generally have higher material quality and performance.

3. Manufacturing Process Differences

Black Iron Pipes: Black iron pipes are almost exclusively manufactured using the straight seam resistance welding (ERW) process. Steel plates are rolled into shape, then the edges are heated by electric current and pressure welded together. The process is relatively simple and low-cost.

Black steel pipes are mainly divided into two types according to their production process:
Welded Black Steel Pipes: These include black iron pipes (ERW) and larger diameter or thick-walled pipes manufactured using processes such as submerged arc welding (SAW).

Seamless Black Steel Pipes: These are made by piercing solid round steel, hot rolling, or cold drawing, without weld seams. Their pressure resistance, uniformity, and reliability are generally superior to welded pipes, making them suitable for more demanding working conditions (such as high pressure and high temperature).

Price: The production cost and price of seamless steel pipes are generally higher than those of welded steel pipes.

4. Application Differences

Black Iron Pipes – Low-Pressure Fluid Transportation

a. Construction: Indoor fire-fighting water pipes, domestic water pipes (now mostly replaced by galvanized pipes and plastic pipes), heating pipes.
b. Municipal: Low-pressure gas pipes, drainage pipes.
c. Protection: Conduit pipes, scaffolding (but nowadays, specialized scaffolding steel pipes are more commonly used).

Black steel pipes: Extremely wide range of applications, covering almost all industrial sectors.

a. Transportation applications: High-pressure steam, oil and gas pipelines (seamless pipes), chemical media, structural support.
b. Structural applications: Mechanical equipment frames, factory steel structures, bridge components, vehicle beams, etc.
c. Machining: Used as blanks for shafts, cylinders, and hydraulic supports.

5. Appearance and Corrosion Protection

Both types have a layer of black iron oxide scale (Fe3O4) on their surface when they leave the factory. This scale has some rust-preventive effect, but it is very limited. Exposure to humid air will continue to cause rusting (forming red rust).
Therefore, secondary anti-corrosion treatment is usually required before actual use, such as applying anti-rust paint, asphalt coating, epoxy resin coating, etc.

Conclusion: 

Black iron pipe is actually a type of black steel pipe; it refers to welded black steel pipes used for transporting fluids. If you see a black steel pipe with a clearly visible straight seam, it's very likely a "black iron pipe" or a similar welded black steel pipe. If you can't see the weld seam, it's a seamless black steel pipe and doesn't fall into the category of "black iron pipe."

Main uses of black iron pipes: water/gas pipes, welded, low-pressure, construction sites.

Main uses of black steel pipes: general industrial applications, may be welded or seamless, wide range of uses (transportation or structural).

Read more: Carbon Steel vs Black Steel or Schedule 40 Carbon Steel Pipe