Seamless Steel Pipe for Structural Use

Structural seamless steel pipe is a seamless steel pipe specially used for load-bearing structures such as buildings, bridges, and mechanical supports. Its core features are no welds, high strength, and good mechanical properties. It can withstand static loads, dynamic loads, or complex stress environments. This pipe is widely used in structural fields such as bridges, buildings, power plant boilers, and petrochemical equipment, and has application examples in deep-sea oil and gas development, ultra-deep well drilling, and other scenarios.

Sizes of seamless steel pipes for structural use:

Hot-rolled pipe outer diameter: 32mm~600mm
Cold-drawn pipe outer diameter: 6mm~200mm

Length: Commonly used 6m, 9m, and 12m fixed lengths, and some projects can be customized up to 18m

Classification of structural seamless steel pipes:

Classification by material:

Structural seamless steel pipes are mainly divided into carbon steel, low alloy steel, and special purpose steel according to material. The mechanical properties and applicable environments of different materials are different.

(1) Carbon structural steel: low cost, good weldability, moderate strength, widely used in general buildings and mechanical structures. Common grades: A53A, A53B, SA53A, SA53B, Q235B, Q345B.
(2) Low alloy high strength steel: Add a small amount of alloying elements (such as Mn, Cr, V, Nb) to improve strength, toughness and weather resistance, suitable for heavy loads or harsh environments. Common grades: 16Mn, Q390, Q420, Q460.
(3) Special purpose steel
① Weathering steel: Contains Cu, P, Cr, Ni, forms a dense oxide layer on the surface, resists atmospheric corrosion, and is suitable for outdoor structures (such as bridges and towers). Grade: Corten A/B.
② Low temperature steel: Used for LNG storage tanks and building structures in extremely cold areas. Common grades: 16MnDR (-40℃ low temperature impact toughness), 09MnNiDR (-70℃).
③ Stainless steel: Used for corrosion-resistant structures such as chemical equipment and offshore platforms. Common grades: 304 (0Cr18Ni9), 316 (0Cr17Ni12Mo2).

Classification by production process:

(1) Hot-rolled seamless steel pipe: larger wall thickness (usually ≥5mm), looser dimensional tolerance, low cost, suitable for large structural parts.
(2) Cold-drawn (rolled) seamless steel pipe: high dimensional accuracy, smooth surface, but thinner wall thickness, suitable for precision mechanical structures.

Specific applications of structural seamless steel pipe:

1. Construction field: high-rise building frames, gymnasium trusses, airport structures, docks, stair pillars, highway safety protection, railings, residential buildings, decorative pipes.
2. Bridge engineering: pier supports, suspension bridge components.

3. Machinery manufacturing: used to manufacture seamless steel pipes for pipelines, containers, equipment, pipe fittings and mechanical structures, such as hydraulic supports, engineering machinery arms, and heavy equipment frames. 

4. Industrial: Machinery, solar mounting systems, offshore oil fields, mining equipment, electromechanical hardware, engineering, mining, heavy equipment and resources, process engineering, material handling, and mechanical parts.

5. Other: Agricultural equipment, tower crane structures, wind turbine towers, and temporary support structures.

Ordinary Carbon Structural Seamless Pipe:
Pipes made from carbon structural steel are primarily used for building structures such as factories, bridges, and ships, as well as general fluid transport pipelines.

Low-Alloy High-Strength Structural Steel Pipe:
Compared to ordinary carbon structural steel, low-alloy high-strength structural steel offers advantages such as higher strength, better overall performance, longer service life, wider application range, and greater cost-effectiveness. It is primarily rolled into plates, profiles, and seamless steel pipes, primarily for applications in bridges, ships, pressure vessels (boiler tube), vehicles, and important building structures.

Stainless Steel Structural Seamless Pipe:

Hot-rolled (extruded, expanded) and cold-drawn (rolled) seamless pipes made of stainless steel are used for corrosion-resistant piping and structural components in industries such as the chemical, petroleum, textile, medical, food, and machinery.

What is the difference between structural pipe and fluid pipe?

Structural pipe: Its design is based on the forces it will withstand within the structure (such as bending, compression, and torsion). Engineers are concerned with geometric properties such as section modulus and moment of inertia, as well as mechanical properties such as yield strength. Standards primarily specify minimum mechanical property limits and dimensional tolerances. Hydrostatic testing of each pipe is not required, and is not typically performed.

Fluid pipe: Its design is based on the internal fluid pressure it will withstand. It complies with pressure vessel specifications. A core mandatory requirement of the standard is hydrostatic testing of each pipe. Before leaving the factory, each pipe must withstand a test pressure far exceeding its rated working pressure to ensure it will not rupture or leak during its service life. Controls on chemical composition and defects are also much stricter.

Structural pipe vs. fluid pipe: Can the two be mixed?

Strictly prohibited!

Using structural pipe in fluid transport systems is a significant safety hazard for the following reasons:

1. Leakage risk: Structural pipe does not require tightness. Even if it can withstand pressure, microscopic leaks can cause problems at the joints.
2. Unknown pressure capacity: Structural pipes have not been hydrostatically tested. Tiny defects (such as cracks and inclusions) invisible to the naked eye may exist on the pipe wall. Under pressure, these defects can expand and eventually cause the pipe to burst.
3. Material suitability: The strict control of the chemical composition of fluid pipes ensures their reliability during welding and corrosion resistance in specific media. Structural pipe materials may not possess these properties, leading to weld cracks or accelerated corrosion, further causing catastrophic failure.

Conversely, using fluid pipes as structural components is generally uneconomical. You pay the extra cost for rigorous flaw detection and hydrostatic testing, but these features may be "overkill" for structural applications, and their mechanical properties may be inferior to those of structural pipes designed specifically for structural applications.

Read more: Performance Advantages of Thick-walled Seamless Steel Pipes or Steel Pipe Dimensions & Size Chart