Q345D Fluid Seamless Pipe
Q345D Fluid Seamless Pipe: High-Strength Low-Alloy Steel for Low-Temperature Service
Q345D seamless pipe per GB/T 8163 is a high-strength low-alloy steel designed for fluid transport at low temperatures, offering excellent toughness and weldability.
Hot rolling, cold drawing, normalizing (optional), welding (not for the pipe itself but for fabrication)
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Q345D Fluid Seamless Pipe Introduction
Q345D is a high-strength low-alloy structural steel grade specified for seamless pipes in fluid transportation under GB/T 8163. It is characterized by a minimum yield strength of 345 MPa at ambient temperature and guaranteed impact toughness at -20°C, making it suitable for low-temperature service. The steel provides good weldability and formability, with controlled contents of microalloying elements such as niobium, vanadium, and titanium to refine grain structure and enhance mechanical properties. Typical applications include pipelines for water, oil, gas, and other fluids in pressure systems where toughness and strength are critical.
Q345D Fluid Seamless Pipe Chemical Composition
The chemical composition of Q345D complies with GB/T 1591-2018 for the base steel. Residual elements are strictly controlled to ensure excellent weldability and low-temperature toughness.
- Microalloying elements (Nb, V, Ti) refine grain size.
- Aluminum is added as a grain refiner and deoxidizer.
- Phosphorus and sulfur are kept low to avoid brittleness.
| Element | Specified Value (≤ or range) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.18% | higher strength version of Q345 series |
| Silicon (Si) | ≤ 0.50% | deoxidizer, improves strength |
| Manganese (Mn) | ≤ 1.70% | strengthening and deoxidizing |
| Phosphorus (P) | ≤ 0.030% | impurity, controlled for toughness |
| Sulfur (S) | ≤ 0.025% | impurity, controlled for ductility |
| Niobium (Nb) | ≤ 0.07% | grain refiner, precipitation strengthening |
| Vanadium (V) | ≤ 0.15% | grain refiner, strength |
| Titanium (Ti) | ≤ 0.20% | grain refiner, deoxidizer |
| Chromium (Cr) | ≤ 0.30% | residual, limited |
| Nickel (Ni) | ≤ 0.50% | residual, improves toughness |
| Copper (Cu) | ≤ 0.30% | residual, limited for hot shortness |
| Molybdenum (Mo) | ≤ 0.10% | residual, limited |
| Nitrogen (N) | ≤ 0.012% | controlled to avoid aging |
| Aluminum (Altot) | ≥ 0.015% | grain refinement and deoxidation |
Q345D Fluid Seamless Pipe Thermal and Electrical Physical Properties
These values are typical for Q345D steel and may vary slightly depending on exact composition and heat treatment. They are used for design calculations in fluid service.
- The coefficient of thermal expansion is for the temperature range 20–100°C and 20–200°C as listed.
- Electrical resistivity is measured at room temperature.
| Property | Typical Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | Room temperature |
| Modulus of Elasticity (E) | 206 | GPa | Room temperature, tension |
| Shear Modulus (G) | 79.3 | GPa | Calculated from E and ν |
| Poisson's Ratio (ν) | 0.3 | Room temperature, elastic range | |
| Thermal Expansion Coefficient (α) | 12.0 | 10⁻⁶/K | 20–100°C |
| Thermal Expansion Coefficient (α) | 12.8 | 10⁻⁶/K | 20–200°C |
| Thermal Conductivity (λ) | 45.0 | W/(m·K) | Room temperature |
| Specific Heat Capacity (c) | 470 | J/(kg·K) | Room temperature |
| Electrical Resistivity (ρ_e) | 0.25 | Ω·mm²/m (10⁻⁶ Ω·m) | Room temperature |
Q345D Fluid Seamless Pipe Mechanical Properties
Mechanical properties are verified on pipe samples in the longitudinal direction. Values depend on wall thickness; the table reflects the most common thickness range. Impact test is mandatory at -20°C for Q345D to guarantee low-temperature service.
- Bend test is required for pipes ≤50 mm OD.
- Flattening test may apply to pipes with OD ≤ 400 mm.
| Property | Specified Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥ 345 | MPa | Wall thickness ≤ 16 mm, ambient |
| Yield Strength (ReH) | ≥ 335 | MPa | Wall thickness > 16 to 30 mm |
| Yield Strength (ReH) | ≥ 325 | MPa | Wall thickness > 30 to 40 mm |
| Tensile Strength (Rm) | 470–630 | MPa | All thicknesses |
| Elongation after fracture (A, Lo=5.65√S0) | ≥ 21 | % | Longitudinal, wall thickness ≤ 16 mm |
| Elongation after fracture (A, Lo=5.65√S0) | ≥ 20 | % | Wall thickness > 16 to 40 mm |
| Impact Energy (KV2) | ≥ 40 (longitudinal) | J | -20°C, Charpy V-notch, single value minimum |
| Bend Test (mandrel diameter) | No cracks | Bend angle 180°, mandrel diameter = 3a (a = wall thickness) for OD ≤ 50 mm, cold bending |
Q345D Fluid Seamless Pipe Fully Equivalent Material Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| Europe | EN 10216-2 | P355N | Normalized seamless steel tube for pressure purposes, equivalent strength and low-temperature toughness (–20°C) if N condition |
| International | ISO 3183 | L360NE | Petroleum and natural gas industries – line pipe, requires similar Charpy at –20°C |
| USA | ASTM A333/A333M | Grade 6 | Seamless steel pipe for low-temperature service, with yield ~240 MPa (lower than Q345D), but similar application philosophy; not an exact strength match |
| Russia/CIS | GOST 8732/8731 | 17G1S (17Г1С) | Seamless hot-deformed pipes for structures, similar low-alloy steel with normalized delivery, approx. yield 345 MPa |
Q345D Fluid Seamless Pipe Application Introduction
Q345D seamless pipe is widely adopted in energy, construction, and process industries for its excellent combination of strength and low-temperature toughness. It can be used where operating temperatures may dip to –20°C without risk of brittle failure. Key application areas include:
Product Applications: Fluid transmission pipelines for crude oil, refined products, and natural gas, Fire protection system piping, Compressed air and steam lines, Hydraulic systems in heavy machinery, Process piping in refineries and LNG terminals, Cold-region structural members (hollow sections)
Processed into products: Straight and bent pipe sections, elbows, tees, reducers, Pipe spools and headers, Hydrostatic test loops, Underground water main pipes, Refrigeration piping (ammonia, chilled water), Pump column pipes and suction/discharge lines
Application industries: Oil & gas (onshore/offshore fluid transport, gathering lines), Petrochemical and chemical processing plants, Water supply and distribution (municipal, industrial), Power generation (boiler circulating water, cooling systems), Shipbuilding and marine piping, Mechanical and structural engineering (crane booms, machinery frames)
Q345D Fluid Seamless Pipe Similar / Near-Equivalent Alternative Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 8162 | Q345D | Structural seamless pipe, same base steel but different delivery/application; may substitute for fluid pipe if certified per 8163 |
| Europe | EN 10025-2 | S355J2 | Structural steel plate; not pipe, but equivalent chemistry and toughness class; pipe forms are under EN 10210 or EN 10219 |
| USA | ASTM A572/A572M | Grade 50 | HSLA plate, similar strength but not specifically low-temp certified; pipe equivalents under ASTM A501 if hot-formed |
| Japan | JIS G3454 | STPG 370 (Sch40+) | Carbon steel pipe for pressure service, lower strength (~215 MPa yield) but widely used for comparison |
| India | IS 1239 Part 2 | YST 240/310 | Mild steel tubes; not low-alloy; different strength class |
Notes:
- Q345D pipe is often ordered with normalized heat treatment to consistently meet –20°C impact requirements.
- For wall thickness above 30 mm, confirmation of through-thickness properties may be required (use of Z-quality steel).
- Welding consumables should match the base metal: E5018 or equivalent low-hydrogen electrodes.
- Hydrostatic testing is mandatory per GB/T 8163; non-destructive testing (ultrasonic, eddy current) may be specified.
- Pipes can be supplied with plain ends or beveled ends, with optional protective coatings (varnish, black painting).
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