Round Tube, Round Metal Tubing

Round tube, also known as circular steel pipe, is a long steel bar with a circular (hollow) cross-section. Its core characteristics are a constant outer diameter and wall thickness, with a hollow center. Simply put, it's a hollow round bar.

Round tubes are used in pipelines, thermal equipment, machinery, petroleum and geological drilling, containers, the chemical industry, and specialized applications. Compared to solid round steel, round tubes are lighter, significantly saving material while maintaining the same strength and load-bearing capacity, making them a cost-effective material.

Classification of round steel tube:

1. According to production methods can be divided into seamless round steel tube and welded round steel tube.

Seamless round steel tubes are made by punching solid steel billets and then rolling them, without welds. Seamless tubes offer high pressure bearing capacity and a uniform tube body, but are heavier and more expensive.
Applications: high-pressure boilers, hydraulic systems, oil drilling, and critical structures.

Welded round steel tubes are made by rolling steel plates or strips into a shape and then welding them (such as high-frequency welding or laser welding). Welded steel tubes offer high production efficiency, low cost, and high dimensional accuracy, but they do have potential weaknesses in the weld seams.
Applications: building structures, low-pressure fluid transportation, guardrails, and furniture.

Seamless round steel tube manufacturing process:
Tube Blanks - Inspection - Peeling - Inspection - Heating - Perforation - Pickling - Grinding - Lubrication Air Drying - Welding Head - Cold Drawing - Solution Treatment - Pickling - Pickling Passivation - Inspection

Welding round steel tube manufacturing process:

Strip - Inspection - Shear - Length - Qualitative - Welding - Smoothing - Length - Inspection

2. Classification by material

Carbon steel (CS) round tube: Low cost, moderate strength, and prone to rust.
Common materials: Q235, 20#, 45#, A36, AISI 1018/1045

Low-alloy high-strength steel round tube: High strength, good toughness, and lighter weight. 

Common materials: Q345 (16Mn), Q420, ASTM A572 Gr.50, ASTM A242, S355 (EN), S420

Stainless steel (SS) round tube: Corrosion-resistant, aesthetically pleasing, but high cost.
Common materials: 304/304L, 316/316L, 321

Alloy steel round tube: Specific properties, such as wear resistance and heat resistance.
Common material: 20CrMnTi, 40Cr, 35CrMo, 42CrMo, AISI 4140/4130, 41Cr4, 34CrMo4, 42CrMo4, 18CrNiMo7-6

3. Classification by application

Structural tubes: Require mechanical properties—strength and stiffness.
Common standard: ASTM A500

Fluid transport tubes: Sealing and pressure-bearing capacity.
Common standard: ASTM A106, ASTM A53

Machining tubes: Dimensional accuracy and surface quality.
Common standards: ASTM A519, DIN 2391, EN 10305

Special purpose tubes: Specific properties—high and low temperature resistance, corrosion resistance.
API 5L (line pipe)
ASTM A213 (boiler pipe)

Advantages and Disadvantages of Round Steel Tube:

Advantages:
1. Excellent cross-sectional properties: With the same bending and torsional strength, it is significantly lighter than solid round steel, resulting in high material efficiency.
2. Good mechanical properties: Isotropic, with uniform strength and stiffness in all directions.
3. Low fluid resistance: The smooth inner surface provides low resistance when conveying fluids and reduces energy consumption.
4. Easy processing and connection: Can be easily cut, bent, welded, forged, and machined.
5. Clean and aesthetically pleasing appearance (especially for stainless steel and galvanized pipes).

Disadvantages:
1. Poor corrosion resistance: Carbon steel round tubes are susceptible to rust in humid or corrosive environments and require anti-corrosion treatment (such as galvanizing or painting).
2. Relatively high cost: Compared to some profiles (such as concrete and wood), the initial cost may be higher.
3. Maintenance required: Carbon steel structures require regular maintenance to prevent rust.

Applications of Round Steel Tubes:

1. Architecture and Structures

Large public buildings: Grid structures of stadiums, airport terminals, and exhibition centers.
Industrial and commercial buildings: Factory trusses and structural columns of high-rise buildings.
Auxiliary facilities: Stairs, guardrails, and scaffolding.

2. Machinery and Manufacturing

Fluid Transportation: Pipelines for oil, natural gas, water, and steam.
Mechanical Components: Cylinder barrels for hydraulic and pneumatic cylinders, drive shafts, bearing sleeves, and precision instrument brackets.
Automotive: Shock absorbers, vehicle frames, and drive shafts.

3. Infrastructure and Energy

Bridges: Serving as the primary load-bearing components of piers or arch bridges.
Towers and Masts: Transmission towers, communication towers, and wind turbine towers.
Energy Industry: Superheater tubes for power plant boilers and reactor pipes for petrochemical plants.

4. Daily Life and Furniture

Furniture: Chairs, tables, and bed frames.
Daily Equipment: Fitness equipment, flagpoles, and lamps.

Conclusion:
Round steel tube has become an indispensable foundational material in modern engineering due to its efficient material utilization, excellent structural properties, and flexible production methods. The choice of round steel pipe depends on the specific application, budget, and performance requirements (such as strength, corrosion resistance, and precision). Understanding its classification and characteristics is key to correct selection and effective application.

Read more: Carbon Steel Pipe Material and Classification or Square Tube vs. Round Tube: Which is Better?