Seamless Circular Structural Steel Pipes

As a reliable Chinese manufacturer and one-stop supplier of steel structural components, HAISHENG offers seamless circular structural steel pipes from stock. These pipes are formed from solid billets through processes such as hot rolling and cold drawing, resulting in a seamless, unitary structure. They comply with standards such as GB/T 8163 and GB/T 6479, with common material grades including 20# and Q355B.

What are the characteristics of seamless circular structural steel pipes?

I. Mechanical and Structural Characteristics

1. Formed via integral rolling and piercing without weld seams; the pipe wall features a uniform, dense microstructure and stable omnidirectional load-bearing capacity. They far outperform welded pipes in terms of high-pressure resistance, high-temperature tolerance, and fatigue resistance.

2. Excellent sealing and pressure-bearing capabilities, with outstanding resistance to leakage and bursting, making them suitable for continuous, long-term pressurized operations.

3. Smooth inner and outer surfaces, uniform wall thickness, and high structural rigidity; capable of withstanding complex stresses including tension, compression, bending, and torsion.

II. Manufacturing and Performance Advantages

1. Available in hot-rolled and cold-drawn varieties: hot-rolled pipes are suitable for large diameters, thick walls, and high-temperature applications; cold-drawn pipes offer high dimensional precision and superior surface quality, making them ideal for precision machinery and small-diameter piping.

2. Wide range of material options; heat treatments such as quenching and tempering or normalizing can be applied to further enhance strength and toughness, making them suitable for heavy-load and cyclic loading scenarios.

3. Excellent high- and low-temperature performance with a broad operating temperature range; resistant to brittle fracture at low temperatures.

III. Processing and Application Characteristics

1. Suitable for cutting, turning, thread rolling, bending, welding, and heat treatment; excellent machinability makes them ideal for the production of mechanical components and precision pipe fittings. 2. Flexible connection methods: supports flange, threaded, welded, and compression fitting connections to meet various industrial assembly requirements.

3. Can undergo treatments such as galvanizing, anti-corrosion coating, and passivation to enhance corrosion resistance, making them suitable for complex operating environments.

IV. Procurement and Cost Characteristics

1. Complex production processes and relatively low production capacity result in higher prices compared to welded steel pipes of the same specifications.

2. Limited stock of high-end or special specifications; some non-standard sizes require custom manufacturing, leading to longer delivery lead times.

V. Limitations on Use

1. While seamless circular structural steel pipes offer excellent overall performance, they are heavier and require more material than welded pipes of the same specifications, resulting in lower cost-effectiveness for standard low-pressure, ambient-temperature civil applications.

2. Primarily used in critical industrial applications involving high pressure, high temperatures, or hazardous conditions; generally not used for low-load auxiliary components like standard scaffolding or simple guardrails.

Uses and Scope of Application

I. Primary Uses

1. High-pressure fluid transport

Transporting high-pressure water, steam, compressed air, oil, gas, and chemical media; the seamless nature and superior sealing capabilities eliminate leakage risks.

2. Thermal and boiler piping

Used for boiler water walls, superheaters, headers, and main thermal pipeline networks, capable of withstanding high-temperature and high-pressure conditions.

3. Chemical industry and pressure vessel component fabrication

Reactor nozzles, heat exchanger tube bundles, chemical process piping, and corrosion-resistant lines suitable for complex chemical environments.

4. Mechanical component manufacturing

Hydraulic cylinders, pneumatic cylinders, bushings, precision machining blanks, drive shafts, and load-bearing tubular components for construction machinery.

5. Oil, gas, and energy engineering

Oil and natural gas extraction and transmission lines, gathering pipelines, and auxiliary piping for oilfield drilling and extraction.

6. Heavy-duty steel structural components

High-pressure circular pipe columns, heavy-duty trusses, load-bearing equipment supports, and load-bearing tubular components for large machinery.

7. Piping for specialized operating conditions

Low-temperature piping, cryogenic equipment piping, transport lines for flammable or explosive media, and high-pressure fire-suppression piping.

II. Application Scope

1. Power and Thermal Energy: Boiler piping, steam distribution networks, and auxiliary piping for power generation equipment in thermal and cogeneration power plants.

2. Petrochemical Industry: Process pipelines, gathering and transmission lines, and piping components for reaction equipment in refineries, chemical plants, and oil/gas fields.

3. Heavy Machinery: Precision piping components and shaft parts for hydraulic equipment, construction machinery, machine tools, and vehicle manufacturing.

4. Municipal Fire Protection: High-pressure urban fire-fighting piping networks and industrial high-pressure water supply systems.

5. Architectural Steel Structures: Load-bearing column pipes and primary structural members for heavy-duty industrial plants, stadiums, and large-scale trusses.

6. Shipbuilding and Aerospace: Marine propulsion piping, hydraulic systems, and precision tubing for aerospace applications.

7. Refrigeration and Cryogenics: Cold storage facilities, cryogenic equipment, and pipelines for transporting liquid nitrogen or liquid oxygen.

III. Selection Distinctions

· Hot-rolled seamless pipes: Primarily large-diameter and thick-walled; commonly used for high-temperature, high-pressure main pipelines and large load-bearing structural components.

· Cold-drawn seamless pipes: Characterized by smaller diameters, high dimensional accuracy, and smooth surface finishes; commonly used for precision machinery, instrumentation piping, and hydraulic fittings.

Performance Parameters of Seamless Circular Structural Steel Pipes

I. Executive Standards (Commonly Used)

·GB/T 8162: Seamless steel pipes for structural purposes

·GB/T 8163: Seamless steel pipes for fluid transport

·GB 3087: Seamless steel pipes for low and medium-pressure boilers

·GB 5310: Seamless steel pipes for high-pressure boilers

·GB 9948: Seamless steel pipes for petroleum cracking

II. Dimensional Specifications

1) Outer Diameter Range (D)

·Hot-rolled: 219–1200 mm (Common sizes: 57, 76, 89, 108, 159, 219, 273, 325)

·Cold-drawn / Cold-rolled: 6–219 mm (Common precision pipe sizes: 16, 20, 25, 32, 38, 42, 48)

2) Wall Thickness Range (t)

·Hot-rolled: ≥3 mm; maximum thickness can exceed 100 mm

·Cold-drawn: 0.5–10 mm

3) Length

·Hot-rolled: 6–12 m (Typically 9–12 m)

·Cold-drawn: 2–6 m; fixed lengths available

4) Dimensional Tolerances (Typical)

·Outer Diameter: ±0.5 mm or ±1% (whichever is stricter)

·Wall Thickness: +15% / −12.5%

·Cold-drawn Precision Pipe: OD tolerance up to ±0.05 mm; wall thickness ±0.05 mm

5) Theoretical Weight (kg/m)

W=(D−t)×t×0.02466

III. Mechanical Property Parameters (Ambient Temperature, Typical Grades)

1) Carbon Steel Pipes (Grades 10#, 20#)

Grade 10#:

Tensile Strength (Rm): ≥335 MPa

Yield Strength (ReL): ≥205 MPa

Elongation after Fracture (A): ≥24%

Grade 20# (Most Common):

Rm: 410–550 MPa

ReL: ≥245 MPa MPaA: ≥25%

2) Low-alloy high-strength steel (Q345B/Q355B)

·Rm: 470–630 MPa

·ReL: ≥345 MPa

·A: ≥20%

3) Common boiler/high-pressure grades (20G, 15CrMoG, 12Cr1MoV)

·20G: Rm 410–550 MPa, ReL ≥245 MPa

·15CrMo: Rm 440–640 MPa, ReL ≥295 MPa

4) Hardness (HB)

·20#, Q345: Approx. 137–197 HB

·Alloy quenched and tempered steel: 200–280 HB

IV. Pressure and Temperature Parameters

1) Working pressure (empirical values, 20#/GB/T8163)

·Ambient temperature: ≤10 MPa (100 bar)

·Boiler pipe (20G): ≤16 MPa

·High-pressure boiler (12Cr1MoV): Up to 25 MPa+

2) Applicable temperature

·General fluid pipe (20#): −20 to 350°C

·Boiler pipe (20G): ≤450°C

·Heat-resistant alloy (15CrMo/12Cr1MoV): ≤550–580°C

·Low-temperature steel (Q345D): Usable at −40°C

3) Hydrostatic test pressure (standard)

·GB/T8163: P=2⋅σ⋅t/D (σ = 60% of specified yield strength); typically 6–10 MPa, held for 10–30 s

V. Physical Properties (Approximate at ambient temperature)

·Density: 7.85 g/cm³

·Modulus of elasticity: 2.06×10⁵ MPa

·Poisson's ratio: 0.3

·Thermal conductivity: Approx. 45 W/(m·K)

· Coefficient of linear expansion: approx. 12 × 10⁻⁶ /°C

VI. Manufacturing Process and Surface Quality

· Seamless (no weld seams); uniform microstructure; free from strength weaknesses associated with weld seams

· Cold-drawn: smooth surface finish (Ra 3.2–12.5 μm); high dimensional precision

· Hot-rolled: heavy surface scale; lower dimensional precision; lower cost