Understanding the Differences Between Steel Pipes and Steel Tubes

Date:2025-01-22Tags:Steel Pipes, Steel Tubes, STD

Steel pipes and steel tubes are both hollow cylindrical structures commonly used in various industries, yet they are distinct in terms of their design, manufacturing processes, applications, and materials. Though people often confuse the two, understanding the differences is essential for selecting the right product for a specific application.

What is Steel Pipes ?

Steel pipes have been in production since the early 1800s and are primarily designed for transporting products such as fluids, gases, pellets, and powders. Their most common applications include underground water and gas transportation systems, plumbing, and as protective conduits for electrical wiring. They are also widely used in the manufacturing of bicycle frames, automobile parts, refrigeration units, and street poles.

The key dimension for steel pipes is the outer diameter (OD), and the wall thickness (WT), which together define the pipe’s capacity. The inside diameter (ID) is calculated by subtracting twice the wall thickness from the outer diameter. Pipes are usually categorized by their wall thickness, with standard schedules such as Sch. 40, Sch. 80, and Sch. XS/XH. Most steel pipes are sold in 24  or 42-foot lengths, with common sizes being based on their ID and schedule.

Steel Tubes Meaning

Unlike steel pipes, steel tubes come in a variety of shapes, including round, square, rectangular, and oval. They are typically used in mechanical applications, pressure equipment, and instrumentation systems. Steel tubes are made from a range of materials such as carbon steel, aluminum, brass, copper, and stainless steel. They can be either seamless or welded, with seamless tubes being produced by piercing a solid block of steel and stretching it into a tube, while welded tubes are made from coils that are slit, rolled into shape, and welded at the seam.

Steel tubes are measured by their outer diameter (OD) and wall thickness (WT), and are commonly sold in 20, 24, 40, or 48-foot lengths. However, custom lengths can also be produced. The manufacturing process for steel tubes tends to be more involved than for pipes, requiring more stringent testing and inspection procedures, which can drive up production costs.



Manufacturing Processes differences between steel pipe and tube

Due to pipe dimension range and applications, the pipe manufacturing processes include seamless (hot rolled or cold drawn) and welded (ERW, LSAW, SSAW).

Tube manufacturing processes usually is in seamless of cold drawn, and welded in ERW. Since tube always in smaller sizes and usually applied in heat-exchanger and mechanical parts, it requires more processes, treatment, and test procedures than pipes. Because of these factors, tube production period is longer than pipe, and not easy for massive production.


Key Differences Between Steel Pipes and Steel Tubes

1.Shape and Diameter


Pipes: Typically round, measured by inside diameter (ID) and wall thickness (WT). They are primarily used for transporting fluids and gases.
Tubes: Available in various shapes, such as round, square, rectangular, or oval. Tubes are calculated by outside diameter (OD) and are often used in structural applications.


2.Applications

Pipes: Primarily designed to carry liquids, gases, and other substances in industries such as plumbing, construction, and energy.
Tubes: Used in a broader range of applications, including mechanical, structural, aerospace, military, and medical fields.


3.Manufacturing Process

Pipes: Generally mass-produced and easier to manufacture, which lowers production costs.
Tubes: Often require more complex manufacturing processes, such as higher precision, more detailed testing, and inspection, resulting in higher production costs.


4.Wall Thickness and Strength

Pipes: Wall thickness is essential in determining the pressure capacity and strength of the pipe. The strength of a pipe is typically defined by its schedule (e.g., Sch. 40, Sch. 80).
Tubes: Wall thickness also plays a crucial role in the strength of the tube, especially when used in structural or mechanical applications.


5.Material Composition

Pipes: Typically made from carbon steel or low alloy steel, with a chemical composition that includes carbon, manganese, sulfur, phosphorus, and silicon.
Tubes: Can be made from various materials, including carbon steel, aluminum, brass, copper, chrome, and stainless steel. The material composition is often tailored to meet specific application requirements.


6.Tolerance and Precision

Pipes: Tolerance levels are crucial, especially for applications requiring precise pressure control for transporting fluids and gases.
Tubes: Tubes often require higher tolerances due to their use in critical structural or mechanical applications, where precision is essential.


7.Cost

Pipes: Generally more affordable due to simpler manufacturing processes and lower material requirements.

Tubes: More expensive due to the complex production methods, higher precision requirements, and the need for rigorous testing.


Pipe has been widely applied in fluids transporting systems, oil and gas industries, thermal and high pressure services.

As pipe emphasize the function of transporting media which under pressure to another place, so pipe always connect with various fittings such as tees, elbows and valves. Such as standards in API 5L, ISO 3183, ASTM A106, ASTM A53, ASTM A333, etc.

Tube is mostly in heat exchanging systems, boiler services, vessels, tube bundle, U tubes, food industries, machinery parts etc. So the tube sizes always in less tolerances than pipe. Tube Standards such as carbon material in ASTM A179, ASTM A192, and stainless steel tube in ASTM A213, ASTM A270 etc.


Size Differences between steel pipe and tube

Pipe is tube which complied with ASNI B 36.10 and B36.19 (for stainless steel). Its diameter represented with NPS which is different from actual diameters.

Pipe wall thickness is indicated by the schedule No. And the same NPS number can have various types of Sch. No. Such as STD, thickened wall thickness (XS) and special thick wall thickness (XXS), and so on.

Tubing refers to finished product meet the standard PG-27.2.1 [Outer diameter D≤5in.(127mm)], and which according calculate formula to select diameter, thickness and according the design.

Piping usually refers to finished product which calculated by PG-27.2.2 formula to select NPS and Sch. No, and follows the design requirements.

Sample of description
Nominal diameter is not the real diameter, real diameter is always larger than the nominal diameter. For example the pipe nominal diameter in 4 inch, wall thickness SCH 40, means the pipe real out diameter is 4 1/2 inch (114.3 mm), real wall thickness 0.237 inch (6.02 mm).

On the contrary, the tube outer diameters described as real OD, for example tube OD 1” means the real diameter is 1 inch.

Meanwhile, the steel pipe applied in the pipeline systems that require large dimensions. Though the pipe size range from 1/2” to 60 inch, in most cases are for the OD above 4 inch. On the other hand, tubes are referred OD below 4 inch, commonly is 1/2 inch, 3/4 inch, 1”, 1 1/2” etc.



Conclusion

Steel pipes and steel tubes may appear similar at first glance, but they are tailored to meet different needs in the industry. Pipes are mainly used for transporting fluids and gases, and they are manufactured to accommodate these specific needs, with a focus on dimensions such as inside diameter and wall thickness. On the other hand, tubes are used in a variety of applications, including structural, mechanical, and aerospace sectors, and are measured by their outer diameter.

Understanding the differences in shape, manufacturing, material, and application is crucial for selecting the right product for a given task. Whether it’s for construction, transportation, or specialized equipment, recognizing these distinctions ensures that steel pipes and tubes are used efficiently and effectively in their respective roles.

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