Stainless Steel Helical Coil Tube — Coiltube for Heat Transfer Applications
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd | Product Code: 964
1. Product Overview
The Stainless Steel Helical Coil Tube (Coiltube) is a precision-engineered tubular product designed for advanced heat exchange systems. Unlike conventional straight-pipe heat exchangers, helical coil tubes exploit the unique hydrodynamic and thermal characteristics of curved flow channels to achieve superior heat transfer coefficients, compact volumetric efficiency, and enhanced fluid mixing. The coiled geometry induces secondary Dean vortices within the fluid stream, which significantly intensify turbulent mixing and reduce thermal boundary layer thickness — resulting in heat transfer rates that can exceed those of equivalent straight pipes by 20%–40%.
This product line encompasses a wide range of coil configurations — from tightly wound micro-coils for laboratory-scale reactors to large-diameter helical coils for industrial process heat exchangers. All products are manufactured to meet or exceed international standards including ASTM A213, EN 10217, and GB/T 14976.
2. Material & Properties
2.1 Available Grades
| Grade | UNS Designation | Composition (Key Elements) | Key Characteristics |
|---|---|---|---|
| 304 / 0Cr18Ni9 | S30400 | Cr: 18–20%, Ni: 8–10.5% | General corrosion resistance, good formability |
| 316 / 0Cr17Ni12Mo2 | S31600 | Cr: 16–18%, Ni: 10–14%, Mo: 2–3% | Enhanced pitting resistance, chloride tolerance |
| 316L / 00Cr17Ni14Mo2 | S31603 | Cr: 16–18%, Ni: 10–14%, Mo: 2–3%, C ≤ 0.03% | Welding-grade, low carbon, superior post-weld performance |
| 321 / 0Cr18Ni11Ti | S32100 | Cr: 17–19%, Ni: 9–12%, Ti: 5×C | Stabilized against sensitization, high-temperature service |
| 347 / 0Cr19Ni11Nb | S34700 | Cr: 17–19%, Ni: 9–12%, Nb: 10×C | Nb-stabilized, excellent creep resistance |
| 904L | S31503 | Cr: 19–23%, Ni: 23–28%, Mo: 4–5% | Extreme corrosion resistance, high-temperature oxidation |
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property | Grade 304 | Grade 316L | Grade 321 | Test Standard |
|---|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 485 MPa | ≥ 515 MPa | ASTM A213 / GB/T 228 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ≥ 205 MPa | ASTM A213 / GB/T 228 |
| Elongation (A) | ≥ 40% | ≥ 40% | ≥ 40% | ASTM A213 / GB/T 228 |
| Hardness (HV) | ≤ 210 HV | ≤ 200 HV | ≤ 210 HV | ISO 6507 |
2.3 Physical Properties
- Thermal Conductivity (at 20°C): ~16.3 W/(m·K) for Grade 304
- Specific Heat Capacity: 500 J/(kg·K)
- Thermal Expansion Coefficient: 17.3 × 10-6 /K (20–100°C)
- Density: 7.93 g/cm³
- Maximum Service Temperature: 870°C (Grade 304/316L), 900°C (Grade 321/347)
3. Specifications
3.1 Geometric Parameters
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ114.3 mm | ASTM A213 / EN 10217-7 |
| Wall Thickness | 0.3 mm – 6.0 mm | ASTM A213 |
| Coil Diameter (Helix Mean Diameter) | 50 mm – 3000 mm | Custom / Project Specification |
| Coil Pitch (Helix Pitch) | 10 mm – 200 mm | Custom / Project Specification |
| Coil Length (Uncoiled) | 5 m – 500 m (continuous) | — |
| Coil Turns | 5 – 5000 turns | — |
| Surface Finish | 2B, BA, No.4, No.8, Mirror (#7) — Ra ≤ 0.05 μm | ASTM A480 / EN 10088 |
| End Treatment | Plain end, Beveled, Threaded (NPT/BSP), Flanged | ASME B1.20.1 / ISO 7 |
| Tolerance — OD | ±0.05 mm (precision) / ±0.1 mm (standard) | EN 10217-7 |
| Tolerance — Wall Thickness | ±10% (standard) / ±5% (precision) | EN 10217-7 |
3.2 Form Conditions
- Annealed (Solution Treated): Maximum ductility, stress-relieved after forming
- Cold Worked (Hardened): Enhanced mechanical strength, 1/4H, 1/2H, Full Hard
- Stress-Relieved: Post-coiling thermal treatment to eliminate residual stresses
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection — Certification-grade stainless steel seamless tubes or welded tubes (ERW/LSW) conforming to ASTM A213 or equivalent.
- Hydroforming / Cold Drawing — Tubes are drawn to precise OD and wall thickness tolerances. For thick-walled coils, hydroforming ensures uniform wall distribution.
- Solution Annealing — Tubes are heated to 1050–1150°C in a protective atmosphere (or vacuum) furnace, followed by rapid quenching to achieve a uniform, carbide-free microstructure.
- Coiling / Helical Forming — Tubes are formed into helical coils using precision CNC-controlled coiling machines. The forming process is designed to minimize cross-sectional distortion (ovality control ≤ 2% of OD) and maintain dimensional accuracy throughout the coil.
- Post-Coiling Stress Relief — Coils are subjected to low-temperature stress relief (400–600°C) to eliminate residual stresses introduced during forming, ensuring dimensional stability during service.
- Surface Treatment — Pickling and passivation to remove oxide scales and form a protective chromium oxide passive layer. Optional electropolishing or mechanical polishing for surface finish requirements.
- Quality Inspection & Testing — Comprehensive non-destructive testing (NDT) and dimensional verification.
- Packaging & Delivery — Coils are secured on wooden reels or steel frames with moisture-barrier wrapping for transport.
4.2 Key Process Controls
- Ovality Control: The helical forming process inherently introduces cross-sectional ovality. Advanced coiling dies and multi-roller forming systems are employed to maintain ovality within 1.5–2.0% of nominal OD.
- Residual Stress Management: Residual stresses from coiling can affect fatigue life and corrosion resistance. Controlled stress-relief annealing cycles are optimized for each grade and coil geometry.
- Grain Structure Integrity: The cold forming process is designed to avoid excessive work hardening that could promote sensitization or intergranular corrosion susceptibility.
5. Applications
5.1 Heat Exchange Systems
Helical coil tubes are the primary heat transfer element in a wide range of heat exchanger designs. The curved geometry promotes secondary flow (Dean vortices), which enhances turbulence and significantly improves convective heat transfer coefficients — particularly at low to moderate Reynolds numbers where straight-pipe performance is limited by laminar flow conditions.
- Air-Condenser Heat Exchangers — Refrigerant coil tubes in HVAC systems
- Shell-and-Coil Heat Exchangers — Process fluid heating/cooling in chemical plants
- Plate-and-Coil Heat Exchangers — Compact high-efficiency heat recovery units
- Reboilers and Condensers — Distillation columns in petrochemical processing
5.2 Process Engineering
- Continuous Reactor Coils — Exothermic/endothermic reaction control in polymerization, hydrogenation, and oxidation processes
- Ejector and Steam-Trap Coils — Condensate management in steam systems
- Evaporator Coils — MVR (Mechanical Vapor Recompression) systems for seawater desalination
5.3 Specialized Applications
- Food & Pharmaceutical Industry — Pasteurization, sterilization, and CIP (Clean-in-Place) compatible coils (Ra ≤ 0.4 μm)
- Power Generation — Feedwater heating coils, economizers, and superheater elements
- Oil & Gas — Subsea heat exchange coils, process cooling in offshore platforms
- Automotive — Exhaust gas recirculation (EGR) cooler coils, turbocharger intercoolers
- Cryogenic Systems — Liquefaction coils for LNG and hydrogen processing (Grade 304L/316L)
6. Quality Certifications & Standards Compliance
6.1 Manufacturing Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management
- TÜV — Certified manufacturing facility
- CE Marking — Conformity with European Machinery Directive
6.2 Product Testing & Inspection
| Test Method | Standard | Purpose |
|---|---|---|
| Chemical Analysis (Spectroscopy) | ASTM E415 / GB/T 20123 | Composition verification |
| Hydrostatic Pressure Test | ASTM A213 / EN 10216-5 | Leak-tightness and structural integrity |
| Eddy Current Testing (ECT) | ASTM E709 | Surface and near-surface defect detection |
| Ultrasonic Testing (UT) | ASTM E213 | Internal defect detection (inclusions, laminations) |
| Dimensional Inspection | EN 10217-7 | OD, wall thickness, ovality, straightness |
| Intergranular Corrosion Test | ASTM A262 / GB/T 4334 | Weld decay / sensitization resistance |
| Pitting Corrosion Test | ASTM G48 / EN ISO 6508 | Pitting resistance (PREN verification) |
| Hardness Testing | ISO 6507 (HV) / ASTM E18 (HRB) | Form condition verification |
| Tensile Testing | ASTM E8 / GB/T 228.1 | Mechanical property verification |
| Surface Finish Measurement | ASTM B851 / ISO 4287 | Roughness profile verification |
6.3 Material Standards
- ASTM A213 / A213M — Stainless Steel Tubing, Seamless and Welded, for High-Temperature and High-Pressure Boilers and Similar Applications
- ASTM A269 / A269M — Stainless Steel Tubing, Seamless and Welded, for Chemical and General Applications
- EN 10217-7 — Tubes for Heat Exchangers and Similar Applications — Stainless Steel