304 Stainless Steel Coil Tube (盘管) — Technical Product Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The 304 Stainless Steel Coil Tube (盘管, Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed as a helically wound or coiled configuration of seamless stainless steel tubing, optimized for applications requiring enhanced surface-area-to-volume ratios, efficient heat transfer, or fluid separation capabilities.
The coil tube geometry is particularly significant in process engineering, where compact flow paths and controlled residence times are critical. As demonstrated in computational fluid dynamics (CFD) studies utilizing ANSYS Fluent for numerical simulation of coil-type separators, the helical configuration induces secondary flow patterns (Dean vortices) that enhance phase separation efficiency, mixing, and thermal exchange compared to straight-tube equivalents.
Wenzhou Jixing Metal Materials Co., Ltd. supplies these coil tubes in a variety of dimensional configurations, serving industries ranging from chemical processing and petroleum refining to food-grade heat exchangers and pharmaceutical equipment manufacturing.
2. Material & Properties
2.1 Base Alloy — AISI 304 / ASTM A213 TP304 / EN 1.4301
The coil tube is fabricated from AISI 304 (UNS S30400) austenitic stainless steel, the most widely used grade in industrial tubing applications. This grade offers an optimal balance of corrosion resistance, formability, and weldability.
2.2 Chemical Composition (wt%)
| Element | Specification |
|---|---|
| Carbon (C) | ≤ 0.08% |
| Manganese (Mn) | ≤ 2.00% |
| Phosphorus (P) | ≤ 0.045% |
| Sulfur (S) | ≤ 0.030% |
| Silicon (Si) | ≤ 0.75% |
| Chromium (Cr) | 18.00 – 20.00% |
| Nickel (Ni) | 8.00 – 10.50% |
| Nitrogen (N) | ≤ 0.10% |
| Iron (Fe) | Balance |
2.3 Mechanical Properties
| Property | Value (Annealed Condition) |
|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa (75 ksi) |
| Yield Strength (Rp0.2) | ≥ 205 MPa (30 ksi) |
| Elongation at Break (A50) | ≥ 40% |
| Hardness (HBW) | ≤ 201 |
| Density (ρ) | 7.93 g/cm³ |
| Thermal Conductivity (λ, 20°C) | 16.3 W/(m·K) |
| Specific Heat (cp, 20°C) | 500 J/(kg·K) |
| Thermal Expansion Coefficient (α, 20–100°C) | 17.3 × 10⁻⁶ /°C |
| Electrical Resistivity (ρe, 20°C) | 7.2 × 10⁻⁷ Ω·m |
2.4 Key Material Advantages
- Corrosion Resistance: The 18% Cr / 8% Ni composition forms a self-healing passive chromium oxide film (Cr₂O₃), providing excellent resistance to atmospheric corrosion, weak acids, and a wide range of organic and inorganic chemicals.
- Formability: The austenitic crystal structure (Face-Centered Cubic, FCC) enables extensive cold working without cracking, essential for the coiling/winding process.
- Weldability: Low carbon content (≤ 0.08%) minimizes sensitization (chromium carbide precipitation at grain boundaries), ensuring intergranular corrosion resistance in welded assemblies.
- Non-Magnetic (Annealed): In the solution-annealed condition, the alloy is essentially non-magnetic (permeability μr ≈ 1.02–1.05), suitable for electromagnetic-sensitive applications.
- Hygienic Compliance: Smooth surface finish (Ra ≤ 0.4 μm available) meets sanitary requirements for food and pharmaceutical processing.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Range / Standard | Notes |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 168.0 mm (¼" – 6") | Custom diameters available upon request |
| Wall Thickness | 0.5 mm – 12.0 mm (0.020" – 0.472") | Thin-wall and thick-wall options |
| Coil Diameter (Mean) | 50 mm – 2,000 mm | Determined by application geometry |
| Coil Length / Total Tube Length | Up to 500 m (1,640 ft) continuous | Spooled or custom-cut |
| Number of Turns | Custom (typically 5 – 5,000 turns) | Designed per process requirements |
| Pitch / Helix Spacing | 1.5× OD – 5× OD (typical) | Optimized for flow/heat transfer |
| End Form | Plain, Beveled, Threaded, Flanged, or Weld Prep | Per customer specification |
3.2 Surface Finish
| Finish Type | Roughness (Ra) | Application |
|---|---|---|
| Commercial (Pickled & Passivated) | ≤ 1.6 μm | General industrial |
| Polished | ≤ 0.8 μm | Chemical processing |
| Electrolytic Polished (EP) | ≤ 0.4 μm | Food, pharmaceutical, biotech |
| Mirror Polished | ≤ 0.2 μm | Decorative, high-purity |
3.3 Applicable Standards
- ASTM A213 / A213M — Seamless austenitic stainless steel tubes for high-temperature service
- ASTM A269 / A269M — Seamless and welded austenitic stainless steel tubing for chemical and general engineering
- ASME SB316 / SB316M (for 316 variants) — Bar and shapes for pressure vessels
- EN 10216-5 — Seamless stainless steel tubes for technical purposes
- GB/T 12771 — Chinese national standard for seamless stainless steel tubes
- JIS G3459 — Japanese standard for seamless stainless steel tubes
- DIN 17456 / DIN 17457 — German standards for stainless steel tubes
3.4 Pressure Rating
Pressure rating is determined by the Barlow equation and applicable code (ASME B31.3 for process piping or ASME BPV Section VIII for pressure vessels). For a typical 304 coil tube with OD = 25.4 mm, wall thickness = 3.0 mm, and allowable stress = 138 MPa (at 20°C):
P = 2 × S × t / D = 2 × 138 × 3.0 / 25.4 ≈ 32.5 MPa (471 psi)
Actual ratings must be verified per project-specific design conditions, including temperature derating, corrosion allowance, and weld joint factors.
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement: High-purity 304 stainless steel billets or slabs sourced from certified mills (e.g., Outokumpu, POSCO, or domestic Chinese producers). Incoming material undergoes spectroscopic verification (OES — Optical Emission Spectroscopy) to confirm chemical composition.
- Piercing & Hot Rolling: Billets are heated to 1,150–1,250°C and pierced to produce seamless tube blanks. Hot rolling reduces the cross-section to near-final dimensions.
- Intermediate Annealing: The hot-rolled tube is annealed at 1,050–1,100°C followed by controlled cooling to restore ductility and refine grain structure (ASTM grain size 5–7).
- Cold Drawing / Cold Reduction: The tube is cold-drawn through precision dies to achieve exact OD and wall thickness tolerances (typically ±0.05 mm for OD, ±0.10 mm for wall thickness). This step also improves surface finish and mechanical properties.
- Final Annealing (Solution Treatment): The cold-worked tube is solution-annealed at 1,040–1,120°C with rapid water quenching to achieve the fully austenitic, soft, and non-magnetic condition.
- Pickling & Passivation: The annealed tube is pickled in a mixed acid bath (HNO₃/HF or H₂SO₄/HNO₃) to remove mill scale and surface oxides, followed by nitric acid passivation to enrich the surface chromium oxide layer.
- Coiling / Winding: The straight tube is helically wound around a mandrel or forming jig to create the coil tube geometry. The winding process is controlled to maintain uniform pitch, prevent tube deformation, and avoid kinking. For larger diameters, CNC-controlled bending machinery is employed.
- End Preparation: Tube ends are cut, beveled (to ASME B16.25 angles), threaded, or prepared for welding per customer specifications.
- Quality Inspection: Comprehensive testing as detailed in Section 6.
- Packaging & Shipping: Tubes are packaged on wooden spools or custom crates with protective end caps, moisture barriers, and proper labeling.
4.2 Coil Forming Considerations
The coiling process introduces bending stresses that must be carefully managed. Key parameters include:
- Minimum Bend Radius: Typically ≥ 5× OD for 304 stainless steel in annealed condition to prevent cracking or ovalization. For smaller OD tubes, this can be relaxed to 3× OD with proper tooling.
- Ovalization Control: Post-coiling ovalization should be maintained below 2% of OD for process applications and below 5% for general use.
- Springback Compensation: CNC winding systems incorporate springback compensation algorithms to achieve the target coil geometry within ±1 mm tolerance.
- Post-Coil Stress Relief (Optional): For applications requiring dimensional stability, a post-coiling stress relief anneal at 850–900°C may be performed.
5. Applications
5.1 Process Separation
As validated through CFD numerical simulation (using ANSYS Fluent with the Reynolds-Averaged Navier-Stokes (RANS) equations and k-ε turbulence model), coil tubes exhibit enhanced separation performance due to the Dean number (De = Re × √(d/D)) effects. The centrifugal force induced in the helical geometry promotes gravitational separation of gas-liquid or liquid-liquid phases, making coil tubes ideal for:
- Gas-liquid separators in natural gas processing
- Oil-water separators in petroleum refining
- Centrifugal condensers in refrigeration systems
- Vapor-liquid contactors in distillation columns
5.2 Heat Exchangers
- Shell-and-coil heat exchangers (coiled tube bundles)
- Plate-and-coil heat exchangers for compact thermal management
- Refrigerant evaporators and condensers in HVAC/R systems
- Organic Rankine Cycle (ORC) evaporators in waste heat recovery
5.3 Chemical & Petrochemical Processing
- Reactor internals and catalyst support tubes
- Corrosion-resistant piping in acid processing plants
- Chlor-alkali industry equipment
- Hydrogen production and storage systems
5.4 Food & Beverage Industry
- Pasteurization and sterilization heat exchangers
- Milk processing and dairy equipment
- Beverage cooling and conditioning systems
- Sanitary-grade fluid transfer coils (3-A and EHEDG compliant)
5.5 Pharmaceutical & Biotechnology
- Bioreactor jacket coils for temperature control
- Crystallizer internals
- WFI (Water for Injection) and purified water distribution
- Pharmaceutical cleaning-in-place (CIP) systems
5.6 Energy & Power Generation
- Boiler economizer coils
- Supercritical and ultra-supercritical steam generator components
- Geothermal heat exchangers
- Fuel cell cooling systems
5.7 Marine & Offshore
- Ballast water treatment systems
- Shipboard HVAC and refrigeration coils