Q420B Steel for LSAW Pipe
Q420B Steel for LSAW Pipe - GB/T 1591 Grade Data, Properties & International Equivalents
Complete material data for Q420B high-strength low-alloy structural steel per GB/T 1591, used in longitudinal submerged arc welded (LSAW) pipes. Covers chemical composition, mechanical & physical properties, equivalent grades, and applications.
Hot rolling, controlled rolling, normalizing; pipe forming by longitudinal submerged arc welding (LSAW) process
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Q420B Steel for LSAW Pipe Introduction
Q420B is a high-strength low-alloy structural steel grade specified in the Chinese standard GB/T 1591 (latest revision 2018). It is extensively utilized for manufacturing longitudinal submerged arc welded (LSAW) pipes—large-diameter, thick-walled pipes critical for the oil & gas, construction, and marine industries. The grade provides a minimum yield strength of 420 MPa, combining excellent strength-to-weight ratio with good weldability and moderate toughness. The "B" designation indicates guaranteed impact energy at +20 °C, suitable for ambient-temperature service. Q420B is typically microalloyed with niobium, vanadium, and titanium to refine grain structure, enhance strength, and maintain weldability. Plates or coils in this grade are used to form and weld LSAW pipes. Delivery condition can be hot-rolled (AR), controlled rolled (CR), or normalized (N), depending on thickness and end use. The resulting pipe is employed in challenging structural applications where high strength, toughness, and cost efficiency are demanded.
Q420B Steel for LSAW Pipe Chemical Composition
Chemical composition of Q420B steel as specified in GB/T 1591-2018. All values are maximum limits unless a range is given. Microalloying elements such as Nb, V, Ti may be added singly or in combination to achieve the required strength and toughness. Nitrogen content is controlled to prevent detrimental effects on toughness. The low carbon equivalent ensures good weldability.
| Chemical Element | Standard Value | Remarks |
|---|---|---|
| C | ≤ 0.20 | Max. for quality grade B |
| Si | ≤ 0.50 | Max. |
| Mn | ≤ 1.70 | Max.; higher Mn may be agreed for improved strength |
| P | ≤ 0.035 | Max. |
| S | ≤ 0.035 | Max. |
| Nb | ≤ 0.07 | Max. |
| V | ≤ 0.20 | Max. |
| Ti | ≤ 0.20 | Max. |
| Cr | ≤ 0.30 | Max. |
| Ni | ≤ 0.80 | Max. |
| Cu | ≤ 0.30 | Max. |
| Mo | ≤ 0.20 | Max. |
| N | ≤ 0.015 | Max. |
| B | ≤ 0.004 | Max.GE |
Q420B Steel for LSAW Pipe Thermal and Electrical Physical Properties
The following physical properties are typical for Q420B-grade low-alloy steel and should be used for general engineering calculations. Slight variations may occur depending on exact composition, heat treatment, and temperature. These values are not part of the product standard but are widely accepted for structural analysis.
| Property | Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Elastic modulus (E) | 206 | GPa | At room temperature |
| Shear modulus (G) | 79.3 | GPa | Derived from E and Poisson's ratio |
| Poisson's ratio (ν) | 0.30 | — | At room temperature, elastic range |
| Thermal expansion coefficient (α) | 12.0 | 10⁻⁶/K | Temperature range 20–100 °C |
| Thermal conductivity (λ) | 45 | W/(m·K) | At 100 °C |
| Specific heat capacity (cp) | 460 | J/(kg·K) | At room temperature |
| Electrical resistivity (ρₑ) | 0.20 | μΩ·m | At 20 °C |
Q420B Steel for LSAW Pipe Mechanical Properties
Mechanical properties of Q420B steel according to GB/T 1591-2018. Values depend on product thickness. Impact test direction and temperature are defined by the quality grade B; specimens are longitudinal unless otherwise agreed. The bending test is performed on a bend angle of 180° with specified mandrel diameters. These properties are verified at room temperature on plate material before pipe forming.
| Property | Standard Requirement Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Yield strength (ReH) | ≥ 420 | MPa | Nominal thickness ≤ 16 mm |
| Yield strength (ReH) | ≥ 400 | MPa | 16 mm < thickness ≤ 40 mm |
| Yield strength (ReH) | ≥ 390 | MPa | 40 mm < thickness ≤ 63 mm |
| Yield strength (ReH) | ≥ 380 | MPa | 63 mm < thickness ≤ 80 mm |
| Yield strength (ReH) | ≥ 360 | MPa | 80 mm < thickness ≤ 100 mm |
| Yield strength (ReH) | ≥ 340 | MPa | 100 mm < thickness ≤ 150 mm |
| Tensile strength (Rm) | 520 – 680 | MPa | All thicknesses |
| Elongation after fracture (A) | ≥ 20 | % | Thickness ≤ 40 mm |
| Elongation after fracture (A) | ≥ 19 | % | 40 mm < thickness ≤ 63 mm |
| Elongation after fracture (A) | ≥ 18 | % | 63 mm < thickness ≤ 100 mm |
| Elongation after fracture (A) | ≥ 17 | % | 100 mm < thickness ≤ 150 mm |
| Impact energy (KV2, longitudinal) | ≥ 34 | J | At +20 °C, thickness ≤ 150 mm |
| Bend test (180°) | d = 3a | — | Thickness ≤ 16 mm (a = sample thickness) |
| Bend test (180°) | d = 4a | — | Thickness > 16 mm |
Q420B Steel for LSAW Pipe Completely Equivalent Standards & Grades
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 1591-2018 | Q420B | Original designation – basis for all comparisons |
Q420B Steel for LSAW Pipe Application Introduction
Q420B LSAW pipe is a versatile product for high-demand structural and fluid transport applications. Its high yield strength and good weldability allow it to be fabricated into a wide range of components for industries where weight savings and reliability are critical. Proper matching of filler metals and welding procedures ensures joint integrity.
Product Applications: Long-distance crude oil / natural gas pipelines, Large-diameter water mains and sewer force mains, Structural pipe columns and truss members, Piling pipe for foundation support, Conductor casing for offshore wells, High-pressure gas cylinders (when further processed)
Processed into products: Line pipe sections (API 5L adapted), Welded tubular structures for bridges, Pipe spools and fittings, Marine risers and J-tubes, Heavy-duty pipe steeve and sleeves, Hydropower penstocks and spiral casings, Offshore jacket structures and piles
Application industries: Oil and gas transmission (onshore and offshore), Civil engineering and construction, Marine and coastal engineering, Shipbuilding, Heavy machinery manufacturing, Power generation (e.g., penstocks, cooling water lines)
Q420B Steel for LSAW Pipe Similar / Alternative Materials for Substitution
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| European Union | EN 10025-3 | S420N | Normalized fine-grain steel, comparable strength and toughness |
| European Union | EN 10025-4 | S420M | Thermomechanical rolled, close yield/tensile properties |
| International | ISO 4950 | E420 | High yield strength structural steel, TMCP type |
| USA | ASTM A572 | Grade 60 [415 MPa] | High-strength low-alloy columbium-vanadium, similar yield (60 ksi); verify composition and CVN requirements |
| Japan | JIS G3106 | SM520B / SM520C | Higher tensile class (520–640 MPa) but lower minimum yield (365 MPa); may be used with engineering adjustment |
Notes:
Welding Considerations: Q420B has a carbon equivalent (CE) typically between 0.38% and 0.42%, providing good weldability with low-hydrogen electrodes and preheating for thick sections. Post-weld heat treatment may be applied as needed. Tolerances: Dimensional and shape tolerances for LSAW pipes are commonly governed by API 5L or customer-specific specifications, not solely by GB/T 1591. Testing: Mechanical properties are validated on plate samples; supplementary tests on pipe weld seam and heat-affected zone may be required per delivery conditions.
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