1. Product Overview
314 stainless steel pipe tube is a heat-resistant austenitic stainless steel product specifically formulated with approximately 2% silicon (Si) content. This silicon addition significantly enhances its oxidation resistance and high-temperature strength, making it an ideal material for boiler systems and other high-heat industrial applications. Unlike standard austenitic grades (e.g., 304, 316), 314 stainless steel is engineered to withstand prolonged exposure to temperatures up to 1050°C (1922°F) without losing structural integrity, making it a reliable choice for critical thermal equipment.
2. Chemical Composition (Key Parameters)
The 2% silicon content is the defining feature of 314 stainless steel, working synergistically with other alloying elements to deliver heat resistance. Below is the typical chemical composition (per ASTM/EN standards):
| Element | Content Range (%) | Function |
| Carbon (C) | ≤ 0.25 | Enhances high-temperature strength and creep resistance |
| Silicon (Si) | 1.50 - 2.50 | Core additive – Improves oxidation resistance at 800-1050°C; forms a dense SiO₂ oxide film to prevent metal degradation |
| Chromium (Cr) | 23.00 - 26.00 | Boosts corrosion and oxidation resistance; forms a protective Cr₂O₃ layer |
| Nickel (Ni) | 19.00 - 22.00 | Stabilizes the austenitic structure; improves ductility and toughness at high temperatures |
| Manganese (Mn) | ≤ 2.00 | Aids in deoxidation during manufacturing; maintains structural stability |
| Phosphorus (P) | ≤ 0.045 | Controlled to minimize brittleness |
| Sulfur (S) | ≤ 0.030 | Controlled to reduce hot cracking risk |
| Iron (Fe) | Balance | Base metal providing structural support |
3. Mechanical & Physical Properties
314 stainless steel pipes excel in high-temperature environments while retaining good mechanical performance at room temperature, making them suitable for both thermal and structural loads in boilers.
3.1 Mechanical Properties (Annealed Condition)
| Property | Value (Typical) | Test Standard |
| Tensile Strength (σb) | ≥ 515 MPa (74,700 psi) | ASTM A249 / EN 10216-5 |
| Yield Strength (σ0.2) | ≥ 205 MPa (29,700 psi) | ASTM A249 / EN 10216-5 |
| Elongation (in 50mm) | ≥ 35% | ASTM A249 / EN 10216-5 |
| Hardness (Brinell) | ≤ 217 HB | ASTM E10 |
3.2 Physical Properties
| Property | Value |
| Density | 7.9 g/cm³ (0.285 lb/in³) |
| Melting Point | 1398 - 1454°C (2548 - 2650°F) |
| Thermal Conductivity (at 100°C) | 15.9 W/(m·K) |
| Coefficient of Thermal Expansion (20-1000°C) | 17.8 × 10⁻⁶/°C |
| Electrical Resistivity (at 20°C) | 7.4 × 10⁻⁷ Ω·m |
3.3 High-Temperature Performance
- Continuous Service Temperature: Up to 1050°C (1922°F) – Suitable for boiler fireboxes, superheater tubes, and flue gas ducts.
- Oxidation Resistance: The 2% Si forms a dense, adherent SiO₂ layer that resists spalling (peeling) even under cyclic heating/cooling, outperforming Si-free grades like 309S.
- Creep Resistance: Maintains strength under long-term high-temperature loads (critical for boiler tubes under pressure).
4. Specifications
314 stainless steel pipes for boilers are manufactured in various dimensions to meet different boiler designs. Custom sizes are available upon request.
| Specification Type | Range | Notes |
| Outer Diameter (OD) | 6 mm - 630 mm (0.24 in - 24.80 in) | Seamless pipes: 6-630 mm; Welded pipes: 10-2000 mm (for large boiler ducts) |
| Wall Thickness (WT) | 0.8 mm - 50 mm (0.03 in - 1.97 in) | Thicker walls (≥ 5 mm) for high-pressure boiler sections (e.g., water tubes) |
| Length | 3 m - 12 m (9.84 ft - 39.37 ft) | Standard length: 6 m / 12 m; Cut-to-length available |
| Surface Finish | Annealed & Pickled (AP), Bright Annealed (BA), Sandblasted | AP finish is standard for boiler applications (removes scale, improves corrosion resistance) |
5. Manufacturing & Quality Standards
314 stainless steel pipes comply with international standards to ensure consistency, safety, and compatibility with global boiler systems.
| Standard Category | Relevant Standards | Scope |
| Material Standards | ASTM A249 (Seamless/Austenitic Stainless Steel Boiler, Superheater, and Heat-Exchanger Tubes) | Defines chemical composition, mechanical properties, and heat treatment for boiler tubes |
| | EN 10216-5 (Seamless Steel Tubes for Pressure Purposes – Part 5: Austenitic Stainless Steels) | European standard for pressure-rated stainless steel tubes |
| | JIS G3463 (Stainless Steel Tubes for Boilers and Heat Exchangers) | Japanese standard for boiler-specific stainless steel tubes |
| Testing Standards | ASTM A480 (General Requirements for Flat-Rolled Stainless and Heat-Resisting Steel Plate, Sheet, and Strip) | Surface quality and dimensional tolerance |
| | ASTM E213 (Eddy Current Testing for Seamless and Welded Tubular Products) | Non-destructive testing (NDT) to detect internal/external defects |
| | Hydrostatic Test (per ASTM A249) | 100% pressure testing (typically 1.5× design pressure) to ensure leak tightness |
6. Similar Grades (Comparison)
314 stainless steel is often compared to other heat-resistant austenitic grades. Below is a summary of key differences to help select the right material:
| Grade | Si Content (%) | Max Service Temp (°C) | Key Advantage vs. 314 | Limitation vs. 314 |
| 314 | 1.5-2.5 | 1050 | Best oxidation resistance; ideal for cyclic high heat | Higher cost than 309S/310S |
| 309S | ≤ 1.0 | 980 | Lower cost; good for moderate high temperatures (≤ 980°C) | Poor oxidation resistance above 980°C |
| 310S | ≤ 1.5 | 1100 | Higher Ni (24-26%) – better creep resistance at 1050-1100°C | Lower Si – oxidation resistance inferior to 314 in cyclic heat |
| 321H | ≤ 1.0 | 870 | Ti-stabilized – resists intergranular corrosion (IGC) | Not suitable for temperatures above 870°C |
Note: For boiler applications with temperatures > 980°C and cyclic heating, 314 is preferred over 309S; for constant high temperatures (> 1050°C) without cyclic stress, 310S may be an alternative.
7. Applications
The 2% Si-enhanced high-temperature resistance of 314 stainless steel pipes makes them indispensable in boiler systems and other heat-intensive industries:
7.1 Boiler-Specific Applications
- Boiler Fireboxes: Withstands direct flame exposure (up to 1000°C).
- Superheater Tubes: Transfers high-pressure steam while resisting oxidation from flue gases.
- Reheater Tubes: Heats steam again after turbine expansion (high cyclic temperature loads).
- Flue Gas Ducts: Carries hot flue gases (800-950°C) without corrosion.
7.2 Other Industrial Applications
- Petrochemical heaters (cracking furnaces).
- Waste incineration plants (high-temperature exhaust systems).
- Thermal power plant heat exchangers.
- Ceramic kilns and industrial ovens.
8. Export Packaging
To ensure 314 stainless steel pipes arrive intact (free from scratches, corrosion, or deformation) during international shipping, we use industry-standard packaging:
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Inner Protection:
- Each pipe is wrapped in PE film (polyethylene) to prevent moisture and surface scratches.
- For polished/bright-annealed pipes, additional kraft paper is used to avoid friction damage.
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Middle Layer:
- Pipes are bundled into coils (for small OD, ≤ 25 mm) or straight bundles (for large OD, > 25 mm) using galvanized steel straps (2-3 straps per bundle) for stability.
- Bundles are lined with corrugated cardboard or plywood sheets to prevent edge damage.
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Outer Packaging:
- Seaworthy plywood crates: Used for straight bundles (max 12 pipes per crate); crates are treated with anti-mold agents and labeled with "防潮" (Moisture-Proof) and "易碎" (Fragile) signs.
- Steel drums: Used for coiled pipes (OD ≤ 25 mm); drums are sealed to prevent water ingress.
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Marking & Documentation:
- Each crate/drum is marked with: Product name (314 Stainless Steel Pipe), OD/WT/Length, quantity, heat number, standard (e.g., ASTM A249), and destination port.
- Shipping documents (commercial invoice, packing list, certificate of origin, material test report/MTR) are placed in a waterproof envelope attached to the crate.
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Special Requirements:
- For cold climates: Additional insulation foam to prevent condensation.
- For long-distance shipping: Container desiccants (silica gel) to absorb moisture.
9. Quality Assurance
All 314 stainless steel pipes undergo strict quality control:
- 100% chemical composition testing (via PMI / Spectroscopy).
- Mechanical property testing (tensile, yield, elongation) on random samples.
- Non-destructive testing (eddy current test, ultrasonic test) for seamless pipes.
- Hydrostatic pressure test for all pipes (per ASTM A249).
- Each batch is accompanied by a Material Test Report (MTR) certifying compliance with standards.
