Stainless Steel Coil Tube (Coil Tube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (also known as Coil Tube or Spiral-Wound Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for demanding thermal-fluid applications. Unlike conventional straight tubes, coil tubes are formed into a continuous helical or spiral configuration, providing superior heat transfer efficiency, compact footprint, and enhanced resistance to thermal stress cycling. This product line is particularly suited for direct-fired steam generators, heat exchangers, and process heating systems where two-phase flow dynamics (liquid-vapor transition) play a critical role in system performance.
The coil tube geometry inherently promotes turbulent flow characteristics within the tube bore, significantly improving convective heat transfer coefficients compared to straight-tube equivalents. The continuous spiral winding also provides inherent mechanical flexibility, accommodating thermal expansion and contraction without requiring additional expansion joints, thereby reducing system complexity and potential failure points.
2. Material & Properties
Wenzhou Jixing Metal Materials Co., Ltd. offers coil tubes fabricated from a range of austenitic and duplex stainless steel grades, selected based on the specific service environment and thermal requirements:
- SUS304 / AISI 304 (UNS S30400) — General-purpose corrosion resistance; suitable for non-aggressive chemical environments and moderate-temperature steam generation.
- SUS316L / AISI 316L (UNS S31603) — Enhanced resistance to pitting and crevice corrosion due to molybdenum (Mo) alloying; preferred for chloride-containing or marine environments.
- SUS321 / AISI 321 (UNS S32100) — Titanium-stabilized grade offering excellent resistance to intergranular corrosion at elevated temperatures (up to 870 °C / 1600 °F).
- SAF 2205 (UNS S31803) — Duplex austenitic-ferritic stainless steel providing higher yield strength (≈ 450 MPa) and superior resistance to stress corrosion cracking (SCC).
Key Material Properties (Typical Values for SUS316L)
| Property | Symbol | Value | Unit |
|---|---|---|---|
| Yield Strength (0.2% Offset) | σ0.2 | ≥ 170 | MPa |
| Tensile Strength (Ultimate) | σb | ≥ 485 | MPa |
| Elongation (at fracture) | δ5 | ≥ 40 | % |
| Thermal Conductivity (20 °C) | k | 14.6 | W/(m·K) |
| Thermal Conductivity (500 °C) | k | 23.0 | W/(m·K) |
| Linear Thermal Expansion (20–800 °C) | α | 17.0 | ×10⁻⁶ /°C |
| Density | ρ | 8.0 | g/cm³ |
| Maximum Service Temperature | Tmax | 870 | °C |
3. Specifications
The following table outlines the dimensional and performance specifications for the standard product range:
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 – Φ50.8 mm (0.25" – 2.0") | ASME B36.19M / EN 10217 |
| Wall Thickness | 0.5 – 3.0 mm | ASME B36.19M |
| Coil Diameter (Mean) | Φ100 – Φ2000 mm (customizable) | Manufacturer specification |
| Coil Length (per unit) | 1 – 100 m (continuous coil) | — |
| Coil Pitch | 1.2 – 3.0 × OD | Design-dependent |
| Number of Turns | 20 – 500 turns (per coil unit) | Design-dependent |
| Tolerance on OD | ±0.05 mm (precision grade); ±0.1 mm (standard) | ASTM A269 / ASTM A270 |
| Surface Finish (Internal) | RA ≤ 0.8 μm (electropolished); RA ≤ 1.6 μm (standard) | ASTM A269 |
| Surface Finish (External) | No. 1 (annealed) / 2B (cold-rolled and annealed) | ASTM A480 |
| Maximum Working Pressure | Up to 30 MPa (design-dependent) | ASME BPV Section VIII |
| Operating Temperature Range | −196 °C to +870 °C | Material-dependent |
| Heat Treatment | Solution annealed at 1050–1100 °C, water quenched | ASTM A269 |
| End Preparation | Plain, beveled (37.5°/75°), or socket-welded | ASME B31.3 |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement & Inspection: Hot-rolled stainless steel coils are sourced from certified mills and subjected to spectroscopic analysis (OES) to verify chemical composition compliance with the specified grade (e.g., ASTM A270, EN 10217-7).
- Pipe Forming (Seamless or Welded):
- Seamless route: Hot-rolled billets are pierced, drawn, and cold-drawn to produce seamless tubes meeting ASME B36.19M requirements.
- Welded route: Cold-rolled strip is formed into a tubular shape and TIG (Tungsten Inert Gas) welded, followed by full-penetration weld inspection.
- Cold Drawing & Sizing: Tubes are cold-drawn through precision dies to achieve exact OD and wall thickness tolerances while improving mechanical properties through work hardening.
- Solution Annealing: Tubes are heated to 1050–1100 °C in a protective atmosphere (or vacuum) furnace and rapidly quenched to dissolve carbides, restore ductility, and ensure uniform microstructure free of sensitization.
- Coil Winding (Helical Forming): Straight tubes are wound onto precision CNC-controlled mandrels to form the desired helical geometry. The winding process controls coil pitch, diameter, and number of turns with ±1 mm accuracy. This step is critical for applications involving two-phase flow in direct-fired steam generators, where coil geometry directly influences flow distribution and heat transfer uniformity.
- Surface Treatment (Optional): Electropolishing or passivation treatment is applied to internal surfaces to achieve low roughness (RA ≤ 0.8 μm), enhancing flow efficiency and reducing fouling tendency in steam and process fluid applications.
- Quality Inspection & Testing:
- Visual and dimensional inspection (100%)
- Hydrostatic pressure testing (100%, at 1.5× working pressure)
- EDDY current testing for wall thickness and defect detection
- RT (Radiographic Testing) or UT (Ultrasonic Testing) for weld integrity
- Chemical analysis (OES) and mechanical testing (tensile, hardness)
- Packaging & Dispatch: Coils are wrapped in moisture-proof protective film, crated in wooden or steel containers, and labeled with material certificates and traceability markings.
5. Applications
The stainless steel coil tube product line from Wenzhou Jixing Metal Materials Co., Ltd. serves a broad spectrum of industrial applications, with particular emphasis on thermal-fluid systems:
5.1 Direct-Fired Steam Generators
In direct-fired steam generators, coil tubes serve as the primary heat transfer elements where combustion gases heat process fluid through the tube wall. The coil geometry is specifically designed to manage the two-phase flow region (evaporation zone), where liquid transitions to vapor. Key design considerations include:
- Uniform heat flux distribution along the coil length
- Control of void fraction evolution to prevent flow instability (density-wave oscillation)
- Minimization of flow maldistribution in multi-tube configurations
- Adequate wall temperature margin to prevent film boiling or dryout
The calculation model for the two-phase section involves solving coupled equations for mass, momentum, and energy conservation along the coil, accounting for frictional pressure drop (Darcy-Weisbach), gravitational head, and acceleration pressure drop due to vapor generation.
5.2 Additional Application Areas
- Heat Exchangers: Spiral-wound heat exchangers for liquid-liquid and liquid-gas heat transfer in chemical processing, petrochemical, and pharmaceutical industries.
- Process Heating & Cooling: Coil tubes embedded in reaction vessels or jacketed equipment for precise temperature control.
- Food & Beverage Industry: Sanitary-grade (316L, electropolished) coil tubes for milk pasteurization, beer brewing, and food-grade fluid heating.
- Pharmaceutical Industry: CIP (Clean-in-Place) and SIP (Sterilize-in-Place) compatible coil assemblies for process fluid conditioning.
- Power Generation: Superheater and reheater coils in waste-heat recovery (WHR) boilers and cogeneration systems.
- Marine & Offshore: Corrosion-resistant coil tubes for seawater heat exchangers and desalination systems.
- Aerospace: Lightweight, high-performance coil tubes for fuel conditioning and thermal management systems.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and certifications ensuring product reliability and regulatory compliance:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Design, manufacture, and supply of metal products |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| ASME "S" Stamp | Section I — Power Scattered Parts (for pressure vessel components) |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for EU market |
| EN 10204 3.1 | Inspection Certificate — Test report based on inspection by authorized quality control personnel |
| NORSOK M-650 | Oil & Gas — Materials for sour service (if applicable) |
| ASTM A269 / A270 | Standard specifications for austenitic stainless steel seamless and welded tubes |
| EN 10217-7 | Non-ferrous metallic materials — Tubes for heat exchangers (stainless steel) |
| DIN 17457 / DIN 17458 | German standards for stainless steel tubes (cold-drawn and hot-finished) |
7. Unique Selling Points
- Engineering Expertise in Two-Phase Flow: Deep understanding of coil tube performance in direct-fired steam generators, including validated two-phase section calculation models for accurate thermal-hydraulic design.
- Customizable Coil Geometry: CNC-controlled winding allows precise customization of coil diameter, pitch, and turn count to match specific thermal design requirements.
- Multi-Grade Material Availability: In-stock and made-to-order supply across 304, 316L, 321, 347, and duplex 2205 grades with full traceability.
- Full Traceability: Each coil tube batch is accompanied by a complete material certificate (EN 10204 3.1) with heat number, chemical analysis, mechanical test results, and dimensional inspection data.
- Surface Quality Excellence: Optional electropolishing achieves internal surface roughness of RA ≤ 0.8 μm, critical for high-efficiency heat transfer and hygienic applications.
- One-Stop Supply: From raw material selection through precision manufacturing, testing, and packaging — reducing customer procurement complexity and supply chain risk.
8. Technical Notes
Note on Two-Phase Section Design: When coil tubes are employed in direct-fired steam generators, the two-phase (evaporating) section requires careful hydraulic and thermal design. The calculation model typically involves discretizing the coil into axial segments and solving for local void fraction (α), mixture velocity (um), frictional pressure gradient (dPf/dz), and heat flux (q''w). Key correlations include the Lockhart-Martinelli two-phase multiplier (φlo²), the Chisholm B-parameter, and the Dittus-Boelter or Gnielinski equation for single-phase segments. Coil curvature introduces centrifugal effects that modify secondary flow patterns (Dean vortices), enhancing radial mixing and heat transfer beyond straight-tube predictions.