Is black iron pipe the same as black steel pipe?

Black iron pipe and black steel pipe are two types of pipes commonly used for plumbing, gas lines, sprinklers, and other applications. While they may look similar at first glance, there are some key differences between black iron and black steel pipe that impact their performance, cost, and ideal use cases.

What is Black Iron Pipe?

Black iron pipe is made of cast iron or ductile iron that has been dipped in a protective black coating. The black coating helps prevent rusting and corrosion. Iron pipe has been used for plumbing and gas lines since the 1800s.

Here are some key characteristics of black iron pipe:

• Made of cast iron or ductile iron
• Has a black protective coating
• Available in different weights or thicknesses (e.g. Schedule 40, Schedule 80)
• Used for plumbing, gas lines, fire sprinkler systems
• Rigid and brittle – difficult to bend and cut
• Prone to rusting if coating is scratched
• Interior has rough surface due to casting process

Black iron pipe is sold in standard lengths of 21 feet. It requires threading to join pipes and fittings. Pipe sizes range from 1/8″ to 24″ diameter. Larger diameter pipes have thicker walls to maintain strength.

What is Black Steel Pipe?

Black steel pipe is made of carbon steel that has been dipped in a protective black coating. The coating helps resist corrosion. Steel pipe became more common in the late 1800s as manufacturing improved.

Here are some key characteristics of black steel pipe:

• Made of carbon steel
• Has a black protective coating
• Available in different weights or thicknesses (e.g. Schedule 40, Schedule 80)
• Used for plumbing, gas lines, sprinklers, structural applications
• More flexible than cast iron – can be bent and cut easier
• Prone to rusting if coating is damaged
• Smooth interior finish

Black steel pipe is sold in standard 20 foot lengths. It is joined using welds, flanges, or threading. Pipe sizes range from 1/8″ to 48″ diameter. Schedule 40 is the most common thickness for plumbing.

Key Differences

While black iron and black steel pipe may look similar at first glance, there are some notable differences:

Difference	Black Iron Pipe	Black Steel Pipe
Material	Cast iron or ductile iron	Carbon steel
Manufacturing Process	Cast in a mold	Rolled/welded from sheet metal
Joints	Threaded	Welded, threaded, or flanged
Rigidity	Very rigid and brittle	More flexible and bendable
Interior Surface	Rough due to casting	Smooth due to rolling/welding
Standard Lengths	21 feet	20 feet

In summary, the main differences are that black iron pipe is made of cast iron while black steel pipe is made of carbon steel. Black iron is rigid and brittle with a rough interior surface, while black steel is more flexible with a smooth interior.

Cost Comparison

In general, black iron pipe tends to be more expensive than black steel pipe. Here are some typical costs (in USD per foot):

Pipe Size	Black Iron Pipe	Black Steel Pipe
1/2″	$2.40	$1.20
3/4″	$2.95	$1.60
1″	$3.70	$1.85
1 1/4″	$6.90	$2.30
1 1/2″	$8.50	$2.75

As shown, black iron pipe costs about 2-3x as much as black steel pipe per linear foot in the same diameter. This cost difference results from the more complex manufacturing process for cast iron pipe.

Strength & Pressure Ratings

Both types of black pipe are available in different schedules (wall thicknesses) that determine the maximum pressure rating. Higher schedules indicate thicker walls and higher pressure capacities.

For smaller diameters up to around 8″, black iron pipe and black steel pipe in the same schedule have very similar pressure ratings. However, with larger diameters, black iron pipe tends to have higher pressure capacities.

For example, here are the water pressure ratings for some common pipe sizes and schedules:

Pipe Size	Schedule	Black Iron Pressure Rating	Black Steel Pressure Rating
1/2″	40	850 psi	850 psi
1″	40	850 psi	850 psi
4″	40	430 psi	400 psi
8″	40	290 psi	250 psi
12″	40	220 psi	170 psi

So in summary, black steel pipe is suitable for most low and medium pressure applications. But for higher pressure or larger diameters, black iron provides greater strength.

Corrosion Resistance

The corrosion resistance of black iron vs black steel depends on the type of iron and steel used:

• Cast iron is prone to graphitization corrosion, causing material loss.
• Ductile iron has more corrosion resistance than cast iron.
• Carbon steel is also vulnerable to corrosion.
• Stainless steel varieties resist corrosion better than carbon steel.

The black finish coating on both types provides some initial corrosion protection. However, any scrapes, cracks, or damage to this coating will expose the pipe material to corrosion.

Overall, ductile iron pipe tends to have the best corrosion resistance when the finish coating remains intact. Regular maintenance is required on any black pipe to check for coating damage.

Bendability

Black iron pipe is rigid and brittle, making it difficult to bend. Tight radius bends can crack cast iron pipe. As a result, black iron mainly uses fittings to change direction.

Black steel pipe is far more bendable, allowing for tighter radius bends. This flexibility aids installation, particularly where direction changes are needed.

The bend radius for black steel pipe depends on the material and diameter. But typically Schedule 40 can be bent to around 4-5x the pipe diameter without risk of cracking. This flexibility is a major advantage of black steel over iron.

Flow Characteristics

The interior surface roughness affects fluid flow rate and resistance. Black iron pipe has a rougher surface finish due to the casting process. In contrast, black steel pipe has a smoother surface from rolling/welding.

At higher flow velocities, the smoother interior of black steel results in less friction loss compared to black iron. However, at low flow rates this difference is negligible.

In summary:

• At low flow velocity, black iron and black steel have similar flow characteristics.
• At high velocity, black steel pipe has less friction loss and better flow rate.
• For gas lines, the lower flow resistance of black steel may allow slightly more capacity.

Sound Transmission

The rigid nature of black iron pipe results in more sound transmission or ‘pipe clang’ when compared to black steel pipe. The flexible and dampened acoustic nature of black steel makes it better suited to noise-sensitive applications.

In multi-family construction, building codes often mandate the use of black steel over iron to reduce noise transmission through walls and floors. Black steel helps meet sound transmission class (STC) requirements.

Chemical Resistance

Ductile iron pipe generally has better chemical resistance than carbon steel due to its electrochemical properties. However, stainless steel varieties can also provide excellent chemical resistance.

For applications involving corrosion from acids, alkalis, or salty soils, ductile iron is usually a better choice than carbon steel. The material offers protection when the pipe coating is intact.

If chemical resistance is required, check compatibility charts for the specific iron or steel grade being used. Specialty alloys and coatings can optimize chemical resistance as needed.

Ease of Repair

One advantage of threaded black steel pipe is the ease of making repairs compared to black iron. Damaged sections of black steel pipe can be cut out and replaced with couplings.

With black iron, repairs require cutting out a whole section and threading both ends. The rigid and brittle cast iron is also more prone to cracking during cutting or threading for repairs.

For underground black iron pipe, repairs become very labor intensive since new fittings must be added. This often results in replacement instead of repair.

Sustainability

Both black iron and black steel pipe are highly recyclable materials. However, black steel pipe is often viewed as the more sustainable choice. Reasons include:

• Steel manufacture has lower CO2 emissions than iron.
• Steel contains around 25% recycled content on average.
• Black steel pipe is lighter per foot, resulting in reduced transportation emissions.
• Steel pipe has more scrap value for recycling at end of life.

Many green building standards reward the use of black steel pipe over iron for plumbing systems due to its sustainability benefits.

Code Approvals

Both black pipe varieties carry code approvals from organizations like ASTM International and Underwriters Laboratories (UL) for applications such as:

• Potable cold and hot water plumbing
• Natural gas and liquid propane gas lines
• Compressed air systems
• Fire protection sprinkler systems
• HVAC systems

Always check local plumbing and mechanical codes for the approved pipe types for your application and jurisdiction. The codes reference specific ASTM and UL standards for material grade, schedule, and joining methods.

Installation Considerations

Some key considerations for installation of black iron vs black steel include:

• Black steel requires less heavy lifting equipment due to its lighter weight.
• Steel pipe is easier for one person to maneuver during installation.
• Steel allows bending while iron mainly uses fittings to change direction.
• Iron needs reinforced supports for vertical sections due to weight.
• Steel pipe can be installed at lower temperatures than cast iron.
• Steel’s flexibility reduces risk of cracks from ground shifting or tremors.

In general, black steel pipe is regarded as easier to work with and more forgiving during installation. This makes it popular for do-it-yourself residential plumbing projects.

Usage Examples

Some typical uses of black iron and black steel pipe include:

Black Iron Pipe Uses

• Hot and cold potable water plumbing
• Natural gas lines
• Compressed air lines in workshops
• Fire sprinkler systems in commercial buildings
• Hydronic heating systems
• Large diameter water transmission lines

Black Steel Pipe Uses

• Hot and cold potable water plumbing
• Natural gas lines for residential uses
• Low pressure air and fluid lines
• Structural applications like fence posts
• Mechanical applications like truck frames

Choosing Between Black Iron vs Black Steel

So when should you choose black iron or black steel pipe? Here are some guidelines:

• Black iron for high pressure applications above 250 psi.
• Black iron for larger diameters above 8″ due to higher strength.
• Black iron for fire suppression systems that require rigidity.
• Black steel for low and medium pressure applications.
• Black steel for small to medium diameters.
• Black steel when flexibility for installation is needed.
• Black steel for noise sensitive multi-family projects.

Consider both the pressure rating and chemical compatibility required. Either material can work for residential plumbing in many cases. For critical systems, seek input from an experienced engineer or pipe designer.

Conclusion

Black iron and black steel pipe share some similarities but have distinct differences that matter for performance and cost. Key differences include material strength, rigidity, corrosion resistance, ease of repair, and sustainability impact.

Black iron pipe tends to be used for higher pressure applications and large diameters, while black steel is more flexible and economical for low to medium pressure uses. When selecting pipe, consider not just appearance but the material differences that impact service life and safety.

Both black iron and black steel pipe meet code approval for potable water and gas distribution applications when properly installed. Ensure you adhere to all applicable standards and practices to create safe and durable plumbing and gas systems, regardless of material.