Schedule 40 Black Carbon Steel Pipe

What is Schedule 40 Black Steel Pipe?

Schedule 40 (SCH40) is a standard designation for steel pipe wall thickness grades, typically used to designate carbon steel seamless or welded steel pipe that meets specific wall thickness standards. This standard is primarily used in industrial piping systems, such as those in the oil and gas industries. Wall thickness is calculated using a standard formula, and the specific value is determined based on the pipe diameter and material specifications.

Schedule 40 Black Steel Pipe is a carbon steel pipe that meets the American Standard Wall Thickness Classification (SCH 40). Its surface is a black oxide scale (Fe₃O₄) formed by hot rolling and is uncoated or painted. Its core features are:

Material: Low-carbon steel (carbon content ≤ 0.25%, such as ASTM A53 Gr.B and Q235B).
Wall Thickness: SCH 40 is a medium-grade wall thickness, balancing pressure-bearing capacity and cost.

Surface Finish: Dark gray/black, retaining the natural oxide layer after rolling.

Dimensional Parameters: OD and Wall Thickness (WT) should be consulted according to specific standards (such as the ANSI B36.10 steel pipe size chart). Different pipe diameters correspond to different wall thicknesses.
Applications: Primarily used for conveying fluids such as oil, gas, and water, requiring compliance with certain pressure-bearing and corrosion-resistant requirements.

Advantages of SCH 40 Black Steel Pipe:

1. Cost-Effectiveness: The price of SCH 40 wall thickness is 20%-30% lower than SCH 80 black steel pipe and 40% lower than galvanized pipe.
2. Ease of Processing: Low-carbon steel has good ductility and is easy to cut and weld.
3. Reliable Strength: Meets most low-pressure fluid and structural requirements.

SCH 40 Black Steel Pipe Applications:

1. Construction
Scaffolding uprights, temporary steel structure supports
Ventilation ducts, suitable for dry indoor environments

2. Industrial systems
Low-pressure compressed air piping (≤0.8 MPa)
Cooling water pipes for mechanical equipment (requires anti-corrosion treatment)

3. Municipal engineering
Temporary drainage pipes, suitable for conveying non-corrosive media.

Restrictions on the use of SCH 40 Black Steel Pipe:

Direct use prohibited:
Drinking water systems (substandard hygiene)
Transportation of acidic/alkaline media
Coastal or high-humidity outdoor environments (lifespan <3 years without protection)

Corrosion protection options:
Outdoor use: Epoxy coal tar coating (lifespan extended to 10 years)
Underground installation: 3PE anti-corrosion coating

Frequently Asked Questions about SCH 40 Black Steel Pipes:

1. What pressure can SCH 40 black steel pipes withstand?

The pressure is not a fixed value; it depends on the pipe diameter, material, and temperature. Taking carbon steel at room temperature as an example, common ranges are as follows, but must be calculated according to the ASME standard formula:

Small diameter: Higher (e.g., 1/2″ pipe approximately 15-20 MPa).
Large diameter: Lower (e.g., 6″ pipe approximately 5-8 MPa).

2. Can black steel pipes be directly buried underground or used outdoors?

No, they cannot be used directly. The oxide scale on the surface of black steel pipes does not provide long-term corrosion protection and will rust quickly in humid environments.

a. Buried underground: 3PE anti-corrosion coating, epoxy coal tar coating, etc., are required.
b. Outdoor use: Anti-rust paint (e.g., epoxy zinc-rich primer + topcoat) is required.
c. Dry indoor environment: Short-term use is possible, but basic anti-corrosion treatment is recommended.

3. What is the difference between black steel pipes and galvanized steel pipes? Which should I choose? 

Carbon steel black steel pipes are less expensive, but their surface is untreated and prone to rust, requiring additional anti-corrosion treatment. They are suitable for applications requiring subsequent painting, insulation, underground plastic coating, or use in non-corrosive, dry environments.
Galvanized steel pipes have a silver-white zinc coating and are more expensive. They are suitable for applications exposed to the atmosphere, in humid but not highly corrosive environments, where deep anti-corrosion treatment is not required (e.g., outdoor railings, exposed pipelines).

4. How to choose between SCH 40 and SCH 80 black steel pipes?

It depends on the pressure range of the operating environment.

Choose SCH 40: For low-pressure systems (e.g., ordinary tap water, air conditioning water, low-pressure air). It is the best choice in terms of cost-effectiveness.
Choose SCH 80: For medium- and high-pressure systems (e.g., process piping, high-pressure air), abrasive environments, or applications requiring higher mechanical strength. It is thicker, heavier, and more expensive.

5. Can black steel pipes transport drinking water?

Black pipes (without lining) cannot be used directly for drinking water. Because the inner wall can rust, leading to water pollution, galvanized steel pipes or black steel pipes lined with food-grade epoxy resin must be used for drinking water systems, meeting hygiene standards.

6. What important information needs to be provided when purchasing black steel pipes?

To avoid errors, please clarify the following with the black steel pipe supplier:

Standard and Material: e.g., “ASTM A53 Grade B”.
Dimensions: Nominal diameter, e.g., “DN50” or “NPS 2”.
Wall Thickness: “SCH 40”.
Manufacturing Process: Seamless or ERW (Extended Erector Wound) pipe.
Length: Fixed length (e.g., 6 meters) or custom length.
Ends: Plain end (for welding) or threaded end.
Corrosion Protection Requirements: Whether pre-painted at the factory is required.

Conclusion:

Schedule 40 Black Steel Pipe is a cost-effective general-purpose pipe suitable for short-term or dry environment projects, but requires strict anti-corrosion measures. Key selection criteria include pressure rating, media characteristics, and environmental corrosion assessment.

Note: In engineering and procurement, "SCH 40 black steel pipe" usually refers to general-purpose pipe conforming to ASTM A53 standards. ASTM A106, however, is a material standard specifically designed for high-temperature, high-pressure (>350°C) conditions. Using A106 steel pipe in normal-temperature or low-temperature systems is overkill and wasteful of resources.

Read more: Mild Steel Seamless Pipe or Carbon Steel vs Black Steel