We Super Steel Manufacturing Co.,Ltd(SMC) are amongst the top manufacturers and suppliers for the seamless steel pipe, welded steel pipe, OCTG products and fittings from China. We have been manufacturing and supplying these products to the industry since 1993, and received repeat orders and appreciation from our valued customers.
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Always up to date. In this column you can find the steel pipe related articles, including industry trends, product standards and materials, and some technical guidelines.
The material used for square and rectangular tubes plays a crucial role in determining their performance, durability, and cost. Common materials include plain carbon steel, low-alloy high-strength steel, and stainless steel. Choosing the right material depends on the specific application, working environment, and processing needs. Below is an overview of the commonly used materials for square and rectangular tubes, along with key factors to consider when selecting them.
Common Material Types for Square and Rectangular Tubes
1. Plain Carbon Steel
The most widely used and cost-effective option, suitable for general-purpose structures and components that do not bear heavy loads.
Q235 – The most common plain carbon structural steel in China. The “Q” stands for yield strength, and “235” indicates a minimum yield strength of 235 MPa. It’s widely used in construction, machinery, and general fabrication.
Q195 / Q215 – Lower in strength and cost than Q235, suitable for light-duty structures, decorative frames, or non-load-bearing parts.
ASTM A36 – The U.S. equivalent to Q235, with a yield strength of 250 MPa (≈ 36 ksi). It’s commonly used in structural applications but has slightly different composition limits compared with Q235.
2. High-Strength Low-Alloy Steel
A small addition of alloying elements significantly improves strength, making these steels suitable for critical load-bearing and structural applications.
Q355 (formerly Q345) – China’s most popular high-strength structural steel with a yield strength ≥ 355 MPa. It offers excellent weldability and toughness and is widely used in bridges, buildings, and vehicle frames.
Equivalent Grades:
U.S. – ASTM A500 Grade B/C or ASTM A572 Grade 50
Europe – S355 (EN 10219)
Q390 / Q420 / Q460 – Higher-strength grades designed for heavy-duty applications such as high-rise buildings, large-span structures, and heavy machinery.
3. High-Quality Carbon Structural Steel
20# Steel (AISI 1020) – A classic low-carbon steel (≈ 0.20% C) with better ductility and purity than Q235. Commonly used for shafts, bolts, and structural components that require higher toughness and machinability.
4. Stainless Steel
Chosen for environments demanding corrosion resistance, cleanliness, or aesthetic appeal.
304 (0Cr18Ni9) – The most common stainless steel, known for excellent corrosion resistance and temperature stability. Used in food processing, kitchenware, medical equipment, and outdoor decoration.
304L (00Cr19Ni10) – A low-carbon version of 304 with superior resistance to intergranular corrosion, ideal for welded structures that cannot be heat-treated.
316 (0Cr17Ni12Mo2) – Contains molybdenum for enhanced resistance to acids, alkalis, and pitting corrosion, making it ideal for marine and chemical environments.
201 / 202 – Low-nickel, economical stainless steels with reduced corrosion resistance, suitable for indoor decorative applications.
Key Factors When Selecting Materials for Square and Rectangular Tubes
1) Environmental Conditions
Indoor, dry environments:
Use ordinary carbon steel (e.g., Q235) with paint or electro-galvanizing.
Outdoor exposure:
Choose hot-dip galvanized or weathering steel (e.g., Q355) for better rust resistance.
High humidity or coastal areas:
Opt for hot-dip galvanized steel with a plastic coating or stainless steel (304 / 316).
Chemical environments:
Use 316L or other corrosion-resistant alloys.
High/low temperature conditions:
Select alloy steels designed for the required thermal range.
2) Mechanical Strength Requirements
Light-duty/non-load-bearing parts: Q235 or A36 for lower cost.
Main load-bearing structures: High-strength steels (Q355 or above).
Dynamic or impact-loaded components: Tough steels with high impact energy values (e.g., Q345D, Q390).
3) Processing Requirements
Weldability: Choose steels with a low carbon equivalent (Ceq) to avoid cracking during welding.
Cold bending/forming: Materials must have good ductility and toughness.
4) Standards and Compliance
Ensure materials meet relevant standards:
Construction/bridges: GB/T 1591, EN 10219, ASTM A500.
Export requirements: Comply with destination market standards (ASTM or EN).
Special industries: Shipbuilding, nuclear, and pressure vessel applications may require certified materials.
5) Cost and Budget Balance
Material cost order: Stainless > Weathering > Alloy > Carbon steel.
Initial vs. maintenance cost:
Carbon steel is cheaper initially but requires periodic maintenance; stainless steel has higher upfront cost but minimal upkeep, making it cost-effective in the long term.
Processing cost: High-strength and stainless steels often require specialized tools and welding methods.
6) Aesthetic and Surface Requirements
Visible structures: Choose stainless steel, galvanized, or coated tubes for better appearance.
Concealed parts: Basic rust protection (primer coating) is sufficient.
Weight Calculation for Square and Rectangular Tubes
Accurate weight calculation is essential for design, costing, and transportation.
Formula:
Weight per Unit Length (kg/m) = [(Girth) × Wall Thickness × 7.85] / 1000
The formula is [Volume × Density], where the density of steel is 7.85 g/cm³.
Tips:
Use supplier-provided theoretical weight tables or online calculators for quick estimates.
Note that actual weight may differ slightly due to manufacturing tolerances.
While purchasing and billing are based on actual weight, theoretical weight remains a vital reference for engineering design and budgeting.
Read more: Guide to selecting high-quality square and rectangular tube suppliers
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