What are the three types of steel pipes?

Steel pipes are one of the most widely used materials in maritime, offshore, construction, and industrial applications. But not all steel pipes are the same. The differences in how they are made, what they can handle, and where they perform best can have a direct impact on the safety and efficiency of your project. Whether you are sourcing materials for a vessel, an offshore platform, or an industrial facility, understanding the three main types of steel pipes helps you make the right choice the first time.

What are the three main types of steel pipes?

The three main types of steel pipes are seamless pipes, welded pipes, and electric resistance welded (ERW) pipes. Each is manufactured differently and suited to different applications. Seamless pipes are made without a seam or weld, welded pipes are formed from flat steel plate or strip and joined along a seam, and ERW pipes are a specific category of welded pipe produced using electric current rather than filler material. Knowing which type you need depends on the pressure requirements, the environment, and the specifications of your project.

Beyond the manufacturing method, steel tube sizes also play a critical role in selection. Pipes are classified by their outer diameter, wall thickness, and schedule, which together determine what pressures and loads the pipe can safely handle. We stock pipes across a wide range of steel tube sizes, from small-diameter tubing up to 20 inches, ensuring you can find the right fit regardless of the application.

What is a seamless steel pipe and when is it used?

A seamless steel pipe is manufactured by pushing or pulling a solid steel billet over a mandrel to create a hollow tube. Because there is no weld seam, the pipe has a uniform structure throughout its entire cross-section. This makes seamless pipes exceptionally strong and reliable under high pressure, high temperature, and corrosive conditions.

Seamless pipes are the preferred choice in demanding environments such as:

Offshore oil and gas installations where pressure ratings are critical
High-temperature steam systems on vessels and industrial plants
Hydraulic systems where consistent wall thickness is essential
Chemical processing applications where corrosion resistance matters

In maritime and offshore settings, seamless pipes are often specified under ASTM standards such as ASTM A106 for high-temperature service or ASTM A53 for general structural use. These designations confirm the pipe meets specific mechanical and chemical requirements, which is important for both safety and regulatory compliance.

What is a welded steel pipe and how does it differ from seamless?

A welded steel pipe is formed by rolling flat steel plate or coil into a cylindrical shape and then joining the edges with a weld. The weld runs along the length of the pipe and is clearly visible as a seam. ERW pipes are a common subcategory: they use electric resistance to fuse the edges together without adding filler material, resulting in a clean, strong joint.

Welded pipes are generally more cost-effective than seamless pipes and are widely available across a broad range of steel tube sizes. They are well-suited for lower-pressure applications such as water distribution, structural supports, and general piping systems. However, for applications involving very high pressures or aggressive chemicals, seamless pipes are typically the safer and more appropriate choice.

The key practical difference is this: seamless pipes offer greater structural integrity under extreme conditions, while welded pipes offer better value for standard applications where those extreme conditions are not present. Choosing the wrong type is a costly mistake, which is why working with a supplier who understands the specifications matters.

What’s the difference between schedule 40 and schedule 80 steel pipe?

Schedule refers to the wall thickness of a steel pipe relative to its outer diameter. A higher schedule number means a thicker wall, which means the pipe can handle higher internal pressures. The two most common schedules are schedule 40 and schedule 80.

Schedule 40 pipes have a standard wall thickness that makes them suitable for most general-purpose applications, including water supply, low-pressure gas lines, and structural uses. Schedule 80 pipes have a thicker wall and are used where higher pressure ratings are required, such as in industrial process piping, chemical plants, and some offshore systems.

Both schedule 40 and schedule 80 are available as seamless or welded, and both are produced under ASTM standards. When specifying a pipe, you need to state both the schedule and the outer diameter to ensure you receive the correct steel tube size for your system. Getting this wrong can result in fittings that do not match or pressure ratings that fall short of what the application demands.

Which type of steel pipe is best for marine and offshore use?

For marine and offshore applications, the requirements are demanding. Pipes must resist saltwater corrosion, handle high pressures, and meet strict classification society standards. In most cases, seamless pipes are the preferred choice for critical systems such as fuel lines, hydraulic circuits, and high-pressure steam systems.

Material grade is equally important. Stainless steel pipes offer excellent corrosion resistance for seawater-exposed systems. Carbon steel pipes treated with appropriate coatings are used in structural and lower-risk fluid systems. Copper-nickel alloys are also common in marine piping for seawater cooling circuits, though these fall outside the standard steel pipe categories.

ASTM-certified pipes are widely specified in offshore and maritime projects because they come with documented material properties and traceability. Certifications and material test reports are not optional in these environments. They are a requirement for passing inspections and meeting classification society approvals. You can explore the full range of marine steel products we carry to find the right certified pipe for your specific application.

Where can you source all three types of steel pipe in one order?

Sourcing seamless pipes, welded pipes, and ERW pipes from different suppliers creates unnecessary complexity. It slows down procurement, increases the risk of specification mismatches, and puts pressure on your schedule. For time-sensitive projects, especially in maritime and offshore, this is a risk that is simply not worth taking.

A single supplier who holds broad stock across all pipe types, schedules, and steel tube sizes eliminates that problem. It means one quote, one delivery, and one point of contact who knows the full picture of your order. When fittings, flanges, and other components are also available from the same source, the entire procurement process becomes faster and more reliable.

How Marine Steel helps you source the right steel pipe

We are a Rotterdam-based steel supplier with a second location in Houston, and we stock all three types of steel pipes across a wide range of steel tube sizes and schedules. Whether you need seamless ASTM A106 pipe for a high-pressure offshore system or schedule 40 welded pipe for a construction project, we have it in stock and ready to go.

Here is what we offer:

Full stock coverage across seamless, welded, and ERW pipes in schedule 40, schedule 80, and other schedules, up to 20 inches in diameter
Tube processing and handling services including precision cutting, bending, drilling, rolling, and conservation treatments to your exact specifications or technical drawings
ASTM-certified materials with full documentation and material test reports available on request
One-stop supply including pipes, fittings, flanges, and non-ferrous metals in a single order
Locations in Rotterdam and Houston for fast delivery to vessels, offshore platforms, and industrial sites worldwide

We think along with you from the start. If you are not sure which pipe type or schedule fits your application, our team will help you work it out. You only need to explain your situation once, and we take it from there.