EN10225 S355G9+N Offshore Structural Steel
EN10225 S355G9+N Offshore Structural Steel - Properties, Equivalents & Applications
Detailed datasheet for EN10225 S355G9+N steel plate/coil: chemical composition, mechanical and physical properties, international equivalents, and typical applications in offshore engineering.
Welding, cutting, cold forming, machining, hot forming (followed by normalizing if required)
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EN10225 S355G9+N Offshore Structural Steel Introduction
EN10225 S355G9+N is a thermomechanically rolled or normalized weldable fine-grain structural steel specifically developed for fixed offshore structures. As defined in EN 10225-2, the grade S355G9 offers a minimum yield strength of 355 MPa and enhanced toughness down to -40 °C, making it suitable for critical welded components in harsh marine environments. The '+N' suffix indicates normalizing heat treatment, ensuring uniform mechanical properties and improved resistance to brittle fracture.
- Excellent weldability with controlled carbon equivalent (CEV).
- High impact toughness at low temperatures.
- Strict limits on impurities (S, P) for offshore reliability.
- Available in plates, wide flats, and coils.
EN10225 S355G9+N Offshore Structural Steel Chemical Composition
The chemical composition of S355G9+N is strictly controlled to ensure high weldability and low-temperature toughness. Maximum limits for carbon, phosphorus, and sulfur are low, and grain-refining elements such as Al, Nb, V, or Ti are required. The carbon equivalent (CEV) is limited to guarantee good field weldability.
| Chemical Element | Standard Requirement | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.12% | Typical 0.08–0.10% |
| Silicon (Si) | ≤ 0.50% | Deoxidizer |
| Manganese (Mn) | 1.00 – 1.60% | Strength and toughness |
| Phosphorus (P) | ≤ 0.020% | Strict control for ductility |
| Sulfur (S) | ≤ 0.010% | Strict control for lamellar tearing resistance |
| Chromium (Cr) | ≤ 0.25% | Residual |
| Nickel (Ni) | ≤ 0.50% | Residual |
| Molybdenum (Mo) | ≤ 0.10% | Residual |
| Copper (Cu) | ≤ 0.35% | Residual |
| Aluminium (Al, total) | ≥ 0.020% | Grain refinement |
| Niobium (Nb) | ≤ 0.05% | Grain refinement |
| Vanadium (V) | ≤ 0.10% | Grain refinement |
| Titanium (Ti) | ≤ 0.05% | Grain refinement |
| Nitrogen (N) | ≤ 0.012% | Strict limit to avoid strain aging |
| CEV (max.) | ≤ 0.43% (t ≤ 100 mm) | CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 |
EN10225 S355G9+N Offshore Structural Steel Thermal and Electrical Physical Properties
Physical properties are not specified in the product standard but are typical for low-carbon structural steels. These values are suitable for engineering estimates in design and thermal analysis.
| Property | Typical Value | Unit | Test Condition / Notes |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | Ambient temperature |
| Modulus of Elasticity (E) | 210 | GPa | Tension, ambient |
| Shear Modulus (G) | 81 | GPa | Calculated from E and ν |
| Poisson's Ratio (ν) | 0.3 | - | Elastic range |
| Thermal Expansion Coefficient (α) | 12.0 | 10⁻⁶/K | 20 °C to 100 °C |
| Thermal Expansion Coefficient (α) | 12.8 | 10⁻⁶/K | 20 °C to 200 °C |
| Thermal Expansion Coefficient (α) | 13.5 | 10⁻⁶/K | 20 °C to 400 °C |
| Thermal Conductivity (λ) | 52 | W/(m·K) | At 20 °C |
| Thermal Conductivity (λ) | 48 | W/(m·K) | At 200 °C |
| Specific Heat Capacity (c) | 460 | J/(kg·K) | 20 °C to 100 °C |
| Electrical Resistivity (ρₑ) | 0.22 × 10⁻⁶ | Ω·m | Ambient temperature |
EN10225 S355G9+N Offshore Structural Steel Mechanical Properties
Mechanical properties are verified at ambient temperature on transverse test pieces according to EN 10025-1. The steel exhibits a balance of high strength, excellent ductility, and superior low-temperature impact toughness. Values depend on product thickness.
| Property | Standard Requirement | Unit | Test Condition / Thickness Range |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 355 | MPa | t ≤ 16 mm |
| Yield Strength (ReH) | ≥ 345 | MPa | 16 < t ≤ 40 mm |
| Yield Strength (ReH) | ≥ 335 | MPa | 40 < t ≤ 63 mm |
| Yield Strength (ReH) | ≥ 315 | MPa | 63 < t ≤ 80 mm |
| Tensile Strength (Rm) | 470 – 630 | MPa | t ≤ 100 mm |
| Elongation after fracture (A5) | ≥ 22 | % | t ≤ 40 mm (gauge length 5.65√S₀) |
| Elongation after fracture (A5) | ≥ 21 | % | 40 < t ≤ 100 mm |
| Charpy Impact Energy (KV, -40 °C) | ≥ 50 (longitudinal) / ≥ 27 (transverse) | J | All thicknesses; single values |
| Bend Test (bend angle 180°) | No cracks; mandrel diameter = 3t | - | For all thicknesses |
EN10225 S355G9+N Offshore Structural Steel Direct Equivalent Standards & Substitution Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| European Union | EN 10225-2:2009 | S355G9+N | Normalized; equivalent across CEN members |
| United Kingdom | BS EN 10225-2:2009 | S355G9+N | Identical adoption of EN standard |
| Germany | DIN EN 10225-2 | S355G9+N | Identical |
| France | NF EN 10225-2 | S355G9+N | Identical |
EN10225 S355G9+N Offshore Structural Steel Application Introduction
S355G9+N steel is engineered for the demanding conditions of offshore structures, where high strength, excellent weldability, and guaranteed low-temperature toughness are critical. The normalized condition provides a fine grain structure that resists crack propagation. It is often specified with supplementary Z-quality through-thickness tensile requirements (e.g., Z25, Z35) to prevent lamellar tearing in highly restrained welded joints.
Product Applications: Jacket structures (legs, bracings), Monopile and transition pieces for wind turbines, Deck plate girders and stiffeners, Helideck support frames, Subsea templates and manifolds, Booms and arms for offshore cranes
Processed into products: Welded tubular nodes (Y, K, T joints), Stiffened plate panels, Shear keys and mud mats, Padeyes and lifting lugs, Fatigue-sensitive brackets and connections, Boat landing members
Application industries: Offshore oil and gas extraction, Offshore wind energy, Shipbuilding (special structural sections, e.g., jack-up rigs), Heavy civil engineering (bridges, locks) where offshore standards are adopted
EN10225 S355G9+N Offshore Structural Steel Similar / Comparable Steel Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| EU | EN 10025-3 | S355NL | Similar strength and -50 °C toughness; not specifically rated for offshore welding (lower CEV limit and Z-quality not mandated). |
| EU | EN 10025-4 | S355ML | Thermomechanically rolled; equivalent strength and toughness; may be used if normalizing can be omitted and CEV matches. |
| USA | API 2H | Grade 50 | Offshore structural steel; similar yield strength, but slightly different chemistry and toughness requirements. Requires comparison of CEV and Z-properties. |
| USA | ASTM A572/A572M | Grade 50 [345] | General structural steel; lower toughness and less strict impurity control; not directly substitutable for welded offshore applications. |
| UK (obsolete) | BS 7191 | 355EMZ | Earlier UK offshore steel; similar concept, but replaced by EN 10225. |
Notes:
Additional requirements per EN 10225:
- Optional Z-quality (through-thickness tensile properties) for improved lamellar tearing resistance: Z15, Z25, Z35.
- Welding procedure qualifications must follow appropriate offshore codes (e.g., AWS D1.1, ISO 15614).
- Material certificates according to EN 10204 Type 3.1 or 3.2 are standard.
- Ultrasonic testing to EN 10160 Class S1 or higher may be specified.
- For sheet and coil, tolerances according to EN 10029 class A or B.
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