FH36 LSAW Pipe
FH36 LSAW Pipe: High-Strength Shipbuilding Steel for Cryogenic Applications
In-depth material data for FH36 LSAW pipe, a high-strength steel with excellent low-temperature toughness for shipbuilding and offshore engineering.
TMCP (Thermo-Mechanical Controlled Processing), Normalizing, Quenching + Tempering (optional), Welding (LSAW)
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FH36 LSAW Pipe Introduction
FH36 is a high-strength structural steel specifically designed for shipbuilding and offshore applications, requiring exceptional toughness at sub-zero temperatures down to -60°C. Manufactured into LSAW (Longitudinally Submerged Arc Welded) pipes, it combines high yield strength (minimum 355 MPa) with excellent weldability and ductility. The fine-grained microstructure, achieved through thermomechanical controlled processing (TMCP) or normalizing, ensures reliable performance in harsh marine environments. FH36 LSAW pipes are widely used in critical structural components such as legs of jack-up rigs, columns for offshore platforms, and hull members of ice-class vessels. Its chemical composition is carefully balanced with microalloying elements like niobium and vanadium to enhance strength without compromising toughness.
FH36 LSAW Pipe Chemical Composition
Composition limits according to IACS UR W11 for grade FH36. The steel is fully killed and made to fine grain practice. Aluminum is added for grain refinement, and microalloying elements Nb, V, Ti provide precipitation strengthening. Low carbon equivalent (CEV) ensures good weldability. Residual elements are tightly controlled to maintain notch toughness at -60°C.
| Element | Standard Value (max unless range given) | Remarks |
|---|---|---|
| Carbon (C) | ≤0.16% | Lower for thicker sections to maintain toughness |
| Silicon (Si) | ≤0.50% | Killed steel requirement |
| Manganese (Mn) | 0.90 – 1.60% | Provides solid solution strengthening |
| Phosphorus (P) | ≤0.025% | Strictly controlled for low-temperature ductility |
| Sulfur (S) | ≤0.025% | Strictly controlled for impact properties |
| Aluminum (Al) | ≥0.015% (acid soluble) | Minimum for grain refinement |
| Niobium (Nb) | 0.02 – 0.05% | Microalloy for strength and grain refinement |
| Vanadium (V) | 0.05 – 0.10% | Enhances strength without sacrificing toughness |
| Titanium (Ti) | ≤0.02% | Optional, improves weld heat-affected zone toughness |
| Copper (Cu) | ≤0.35% | May be present; higher levels can affect weldability |
| Chromium (Cr) | ≤0.20% | Residual limit |
| Nickel (Ni) | ≤0.40% | Residual limit; higher Ni may be added for extra toughness |
| Molybdenum (Mo) | ≤0.08% | Residual limit |
| CEV (Carbon Equivalent) | ≤0.38% (typical) | Based on CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 |
FH36 LSAW Pipe Thermal & Electrical Physical Properties
Physical characteristics for FH36 type steel at ambient temperature unless otherwise noted. Data are typical for high-strength low-alloy structural steels and are provided as reference for design calculations. Density is standard for steel. Thermal expansion and conductivity are similar to carbon-manganese steels, and resistivity is typical for ferritic steels. Properties may vary slightly with actual chemical composition and processing.
| Property | Standard Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | At 20°C |
| Elastic Modulus (E) | 210 | GPa | At 20°C |
| Shear Modulus (G) | 80 | GPa | At 20°C |
| Poisson's Ratio (ν) | 0.3 | — | At 20°C |
| Thermal Expansion Coefficient (α) | 11.0 × 10⁻⁶ | /K | From 20°C to 100°C |
| Thermal Conductivity (λ) | 45 – 50 | W/(m·K) | At 20°C |
| Specific Heat Capacity (cₚ) | 460 – 480 | J/(kg·K) | At 20°C |
| Electrical Resistivity (ρₑ) | 0.20 – 0.25 | μΩ·m | At 20°C |
FH36 LSAW Pipe Mechanical Properties
Mechanical properties at room temperature, as required by classification society rules for FH36 steel plates. The values apply to material in normalized or TMCP condition. For LSAW pipes, the pipe body properties are tested on transverse specimens from the base material or longitudinal specimens from the weld zone according to applicable pipe standard (e.g., DNV-OS-F101, API 5L). Impact test temperature is -60°C with minimum average energy 34 J (KV²). Tensile testing per ISO 6892-1.
| Property | Standard Requirement | Unit | Test Condition / Remarks |
|---|---|---|---|
| Yield Strength (ReH) | ≥355 | MPa | Transverse specimen, t ≤ 50 mm |
| Tensile Strength (Rm) | 490 – 620 | MPa | Transverse specimen, all thicknesses |
| Elongation (A5) | ≥21 | % | Gauge length 5.65√So; transverse |
| Impact Energy (KV² at -60°C) | ≥34 (average) / ≥24 (single) | J | Charpy V-notch, longitudinal; for transverse, min 24J average may apply |
| Bend Test (mandrel diameter) | 3 × thickness (t ≤ 25 mm) | — | 180° bend; no cracking |
| Hardness (HV10) | ≤350 (typical for weld area) | HV | Not always mandatory; for sour service qualification |
FH36 LSAW Pipe Fully Equivalent Material Standards & Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| International | IACS UR W11 | FH36 | Unified requirement for ship steels, base for national rules |
| USA | ASTM A131 / A131M | FH36 | Shipbuilding steel; identical toughness class |
| United Kingdom | LR Rules (Lloyd's Register) | FH36 | Specified for low-temperature structural members |
| Norway | DNV Rules (DNV GL) | FH36 | Material designation for offshore and marine steel |
| France | BV Rules (Bureau Veritas) | FH36 | High-strength, low-temperature steel |
| Germany | GL Rules (Germanischer Lloyd) | FH36 | Now part of DNV, historically identical |
| China | CCS Rules (China Classification Society) | FH36 | Same chemical and mechanical limits as IACS |
| Russia | RS Rules (Russian Maritime Register) | FH36 / F36 | Equivalent low-temperature ship steel |
FH36 LSAW Pipe Application Introduction
FH36 LSAW pipes are engineered for demanding environments where both high strength and fracture toughness at cryogenic temperatures are critical. They are specifically designed for welded structures exposed to dynamic loads and temperatures as low as -60°C, making them the material of choice for polar and deepwater applications. The LSAW manufacturing process utilizes rolled FH36 plates formed into cylindrical shape and welded longitudinally, producing pipes with consistent wall thickness and excellent straightness.
- Excellent low-temperature notch toughness prevents brittle fracture in ice-affected regions.
- High yield strength allows for reduced structural weight while maintaining safety margins.
- Good weldability with reduced preheating requirements, suitable for field fabrication.
Product Applications: Longitudinally submerged arc welded (LSAW) pipes (OD 406–1626 mm, wall thickness up to 65 mm), Welded cylindrical sections for structural columns, Tubular nodes and chords for jack-up rig legs, Caissons and riser pipes for deepwater platforms, Piling pipe for coastal and harbor construction
Processed into products: Leg chords and bracings of self-elevating platforms (jack-ups), Main legs and bracings of semi-submersible rigs, Hull longitudinal stiffeners and frames for polar vessels, Transition pieces (TPs) connecting wind turbine tower to foundation, Suction anchors and pile sleeves for mooring systems
Application industries: Shipbuilding (ice-class vessels, LNG carriers, FPSO hulls), Offshore oil & gas (jacket legs, platform columns, conductor pipes), Maritime infrastructure (ice-resistant piled structures, quay walls), Renewable energy (offshore wind turbine foundation transition pieces, monopiles in cold climates), Pressure vessel and storage tank manufacturing (low-temperature service)
FH36 LSAW Pipe Similar / Alternative Material Recommendations
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10025-4 | S460G2+M | Higher strength (460 MPa yield), thermomechanical rolled, good toughness at -20°C (similar to DH/EH classes but not -60°C) |
| International | IACS UR W11 | EH36 | Identical chemistry but impact tested at -40°C; suitable for less severe low-temperature service |
| International | IACS UR W11 | DH36 | Impact tested at -20°C; cheaper alternative when cryogenic toughness is not required |
| International | IACS UR W11 | FH40 | Higher yield strength (390 MPa min) with same -60°C toughness; for weight-saving designs |
| USA | ASTM A131 / A131M | EH40 / FH40 | Increased strength variants of EH36/FH36 for higher load applications |
Notes:
Additional requirements may apply per project specification:
- Impact test requirements for pipe body and weld heat-affected zone (HAZ) may be more stringent (e.g., 42 J average at -60°C).
- Carbon equivalent (CEV) limitation often ≤0.43% for improved weldability.
- Ultrasonic testing (UT) of plates and pipes per EN 10160 or ASTM A578 is commonly mandated.
- For sour service or hydrogen-induced cracking (HIC) resistance, additional chemistry control and HIC testing per NACE TM0284 may be specified.
- Pipe end beveling according to manufacturer's standard or project-specific weld preparation.
- Traceability: full documentation of heat treatment, chemical analysis, and mechanical tests per EN 10204 3.1 or 3.2 certification.
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