S355MLH Structural Hollow Section
S355MLH Structural Hollow Section | EN 10219 Cold-Formed Welded Tube for Arctic Applications
Comprehensive material data for EN 10219 S355MLH structural hollow sections (SHS/RHS). Includes chemical composition, mechanical properties, physical data, and international equivalents for this thermomechanically rolled fine-grain steel with guaranteed impact energy at -50°C.
Cold forming, welding (longitudinal submerged arc or high frequency), bending, machining, hot-dip galvanizing, painting
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S355MLH Structural Hollow Section Introduction
S355MLH is a thermomechanically rolled weldable fine-grain structural steel grade specified in EN 10219 for cold-formed welded structural hollow sections of non-alloy and fine grain steels. The designation 'S355' indicates a minimum yield strength of 355 MPa for thicknesses ≤16 mm, 'M' stands for thermomechanical rolling, 'L' denotes qualified low-temperature impact properties at -50°C (minimum 27 J), and 'H' identifies the product as a hollow section. Typical forms are square hollow sections (SHS), rectangular hollow sections (RHS), and circular hollow sections (CHS). The steel offers high strength, excellent toughness even in arctic conditions, good weldability, and superior formability. It is widely used in bridges, offshore structures, cranes, and heavy machinery where weight savings and low-temperature service are critical. Delivery condition is usually as-welded from cold-formed and longitudinally welded tubes, with optional normalizing or stress-relieving treatments.
S355MLH Structural Hollow Section Chemical Composition
The chemical composition is based on heat analysis according to EN 10219-1. For product thickness ≤40 mm. Typical values for S355MLH are designed to achieve the required mechanical properties through thermomechanical rolling with low carbon equivalent to ensure excellent weldability. Microalloying elements like niobium, vanadium, and titanium may be added for grain refinement.
| Element | Standard Value (max) | Remarks |
|---|---|---|
| Carbon (C) | ≤0.14 | For thickness ≤16 mm; ≤0.16 for 16–40 mm |
| Silicon (Si) | ≤0.50 | |
| Manganese (Mn) | ≤1.60 | |
| Phosphorus (P) | ≤0.025 | |
| Sulfur (S) | ≤0.020 | |
| Nitrogen (N) | ≤0.015 | |
| Aluminium (Al) total | ≥0.020 | Fully killed, fine grain practice |
| Niobium (Nb) | ≤0.05 | Optional grain refiner |
| Vanadium (V) | ≤0.10 | Optional microalloy |
| Titanium (Ti) | ≤0.05 | Optional |
| Chromium (Cr) | ≤0.30 | Residual |
| Nickel (Ni) | ≤0.30 | Residual |
| Molybdenum (Mo) | ≤0.10 | Residual |
| Copper (Cu) | ≤0.35 | Residual |
| Carbon Equivalent (CEV) | ≤0.39 | Typical for fine grain practice |
S355MLH Structural Hollow Section Physical Properties
The physical properties are derived from general data for S355 structural steels, which are representative of S355MLH. Actual values may vary slightly depending on the exact chemical composition and manufacturing process. These values are suitable for engineering calculations.
| Property | Typical Value | Unit | Condition |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | At 20°C |
| Modulus of elasticity (E) | 210 | GPa | At 20°C |
| Shear modulus (G) | 81 | GPa | At 20°C |
| Poisson's ratio (ν) | 0.3 | - | Elastic range |
| Thermal expansion coefficient (α) | 12.0 × 10⁻⁶ | K⁻¹ | 20°C to 100°C |
| Thermal expansion coefficient (α) | 12.5 × 10⁻⁶ | K⁻¹ | 20°C to 200°C |
| Thermal expansion coefficient (α) | 13.0 × 10⁻⁶ | K⁻¹ | 20°C to 300°C |
| Thermal conductivity (λ) | 53 | W/(m·K) | At 20°C |
| Thermal conductivity (λ) | 50 | W/(m·K) | At 100°C |
| Thermal conductivity (λ) | 47 | W/(m·K) | At 200°C |
| Specific heat capacity | 460 | J/(kg·K) | At 20°C to 100°C |
| Electrical resistivity (ρ_e) | 0.20 – 0.25 | Ω·mm²/m | At 20°C |
S355MLH Structural Hollow Section Mechanical Properties
Mechanical properties as required by EN 10219-1 for S355MLH hollow sections at room temperature. Yield strength values depend on wall thickness. The specified minimum values are valid for sections with a wall thickness up to 65 mm; however, for cold-formed hollow sections the thickness is typically ≤40 mm. Impact energy is guaranteed at -50°C.
| Property | Standard Requirement | Unit | Test Condition |
|---|---|---|---|
| Yield strength (ReH) | ≥355 | MPa | Wall thickness ≤16 mm |
| Yield strength (ReH) | ≥345 | MPa | Wall thickness >16 mm ≤40 mm |
| Tensile strength (Rm) | 470 – 630 | MPa | Wall thickness ≤40 mm |
| Elongation (A) | ≥22 | % | Gauge length L0 = 5.65√S0, wall thickness ≤40 mm |
| Impact energy (KV) | ≥27 | J | At -50°C, longitudinal (default) or transverse as specified |
| Bend test (mandrel diameter) | 2t | - | Through 180°, t = wall thickness, for t ≤16 mm; for t >16 mm by agreement |
S355MLH Structural Hollow Section Fully Equivalent Material Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| European Union | EN 10219 | S355MLH | Original specification – cold-formed welded hollow sections |
| United Kingdom | BS EN 10219 | S355MLH | Identical adoption |
| International | ISO 630-3 | S355ML | Base steel grade for plates/strips; same chemical and mechanical requirements, but not for hollow sections. Hollow sections to ISO 10799-2 may use this steel. |
| China | GB/T 1591 | Q355D (or Q355MD) | Approximately comparable; Q355MD is thermomechanically rolled with impact at -20°C (not -50°C). For hollow sections refer to GB/T 6728. |
S355MLH Structural Hollow Section Application Introduction
S355MLH hollow sections are designed for demanding structural applications where high strength, low-temperature toughness, and light weight are required. The combination of thermomechanically rolled steel and the hollow form factor delivers excellent load-bearing capacity with reduced material usage. Typical uses span civil engineering, offshore, heavy machinery, and transport infrastructure.
Product Applications: Welded steel frameworks, Bridge girders and trusses, Offshore platform modules and flare booms, Telescopic crane booms (SHS/RHS), Lattice towers for wind turbines and communication, Structural hollow section columns and beams, Roll-over protective structures (ROPS), Architectural exposed steelwork
Processed into products: Square and rectangular hollow sections cut, drilled, and welded into nodes, Bolted end plates for beam-to-column connections, Welded tubular truss chords and braces, Laser-cut tubular profiles for machine frames and jigs, Bent and formed crane boom sections, Drilled and slotted telescoping arms for extendable booms
Application industries: Construction (bridges, stadiums, high-rise frames), Offshore and marine engineering (platforms, jackets, helidecks), Heavy machinery (crane booms, lifting equipment, chassis), Transportation (rail car underframes, trailer frames), Energy (wind turbine towers, transmission poles, power plant structures), Mining and earthmoving equipment, Agricultural equipment (sprayers, cultivator frames)
S355MLH Structural Hollow Section Similar / Alternative Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| European Union | EN 10210 | S355J2H | Hot-finished hollow section, minimum yield 355 MPa, impact at -20°C; less suitable for extreme low temperatures. |
| European Union | EN 10219 | S355J2H | Cold-formed hollow section, same -20°C impact, non-thermomechanical; lower toughness guarantee. |
| USA | ASTM A500 / A501 | Grade C | Yield 345 MPa, tensile 425 MPa, no low-temperature toughness specification; not equivalent for cryogenic use. |
| Japan | JIS G 3466 | STKR490 | Yield 325 MPa, tensile 490 MPa; not designed for low-temperature toughness. |
| Russia | GOST 30245 | C355 | Similar strength level; check impact requirements (usually -40°C maximum). |
Notes:
- For thicknesses outside the standard range (e.g., >40 mm), mechanical properties shall be agreed upon at the time of enquiry and order.
- The CEV value should be controlled to ensure good weldability; preheat recommendations depend on combined thickness and CEV. Typical CEV ≤ 0.39 permits welding without preheat up to moderate thicknesses under EN 1011-2.
- Corrosion protection: Hot-dip galvanizing of S355MLH is possible, but the high silicon content may affect coating thickness. Alternatively, painting systems according to EN ISO 12944 are widely used.
- Fire resistance design should follow Eurocode 3 (EN 1993-1-2) using the appropriate strength reduction factors at elevated temperature for thermomechanical steels.
- Dimensional tolerances are as per EN 10219-2 (tolerances on shape and dimensions) for the hollow section product.
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