Stainless Steel Spiral Coil Tube — Product Technical Specification
1. Product Overview
The Stainless Steel Spiral Coil Tube (also referred to as Coiltube or Spiral Coil Pipe) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Unlike straight seamless or welded pipes, the spiral coil tube is formed into a continuous helical geometry through a cold-forming process, creating a coil with a consistent helix diameter and pitch. This unique configuration imparts distinct hydraulic and thermal performance characteristics, making it a preferred choice in heat exchanger systems, refrigeration coils, and process piping where compact heat transfer surfaces are required.
Research on the flow characteristics of spiral coil tubes has demonstrated that the helical geometry induces secondary Dean flow vortices within the tube bore, significantly enhancing turbulent mixing and convective heat transfer coefficients compared to equivalent straight tubes. This enhancement—typically 20% to 40% in heat transfer performance—comes with a modest increase in pressure drop, yielding a superior overall thermal-hydraulic efficiency ratio.
2. Material & Properties
2.1 Material Grades
The spiral coil tubes are manufactured from austenitic stainless steel grades conforming to international standards. The primary grades offered include:
- SUS304 / ASTM A269 TP304 — The most widely used austenitic grade, offering excellent corrosion resistance, formability, and weldability. Suitable for general chemical, food, and pharmaceutical applications.
- SUS316L / ASTM A269 TP316L — Low-carbon variant with added molybdenum (Mo 2.0–2.5%), providing superior resistance to pitting and crevice corrosion in chloride-containing environments.
- SUS321 / ASTM A269 TP321 — Titanium-stabilized grade with enhanced resistance to intergranular corrosion at elevated temperatures (up to 870°C).
- SUS310S / ASTM A269 TP310S — High-temperature grade with excellent oxidation resistance, suitable for furnace and high-temperature process applications.
2.2 Mechanical Properties (Typical)
| Property | ASTM A269 TP304 | ASTM A269 TP316L | ASTM A269 TP321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 485 | ≥ 515 |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | ≥ 170 | ≥ 205 |
| Elongation (% min., 50 mm gauge) | ≥ 40 | ≥ 35 | ≥ 35 |
| Hardness (HB max.) | 217 | 217 | 217 |
| Modulus of Elasticity (GPa) | 193 | 193 | 193 |
| Thermal Conductivity (W/m·K, 100°C) | 16.3 | 14.6 | 15.7 |
| Linear Thermal Expansion (×10⁻⁶/K, 20–100°C) | 17.3 | 16.0 | 17.3 |
| Density (kg/m³) | 7930 | 8030 | 7930 |
2.3 Corrosion Resistance
The austenitic microstructure, stabilized by chromium (Cr ≥ 18%) and nickel (Ni ≥ 8%), provides a self-healing passive oxide film that confers excellent resistance to atmospheric corrosion, dilute acids, and organic chemicals. The addition of molybdenum in 316L further enhances resistance to localized corrosion phenomena including pitting and crevice attack in marine and chloride-rich environments.
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm |
| Coil (Helix) Diameter | 100 mm – 1500 mm |
| Coil Pitch (Helical Spacing) | 15 mm – 80 mm |
| Coil Length (per bundle) | 1 m – 30 m (customizable) |
| End Configuration | Plain, Flared, Threaded (BSPT/NPT), or Brazed |
| Surface Finish | 2B, BA (Bright Annealed), Electropolished (Ra ≤ 0.4 μm) |
| Applicable Standards | ASTM A269/A269M, ASTM B730, ASME B31.3, EN 10217-7 |
| Operating Temperature Range | −196°C to +870°C (grade dependent) |
| Maximum Operating Pressure | Up to 4.0 MPa (design dependent) |
| Tolerance on OD | ±0.05 mm (precision grade) |
| Tolerance on WT | ±0.03 mm |
| Coil Diameter Tolerance | ±1.0% |
| Packaging | Wooden crates with desiccant, protective caps on tube ends |
4. Manufacturing Process
The production of high-precision stainless steel spiral coil tubes involves a multi-stage process combining hot-rolled/hot-finished tube blank preparation with cold coiling and post-forming treatments:
- Tube Blank Preparation: Seamless stainless steel tubes are produced via hot rolling or cold drawing processes, conforming to ASTM A269/A269M specifications. Incoming material undergoes chemical composition verification (OES analysis) and mechanical property testing.
- Pre-Treatment / Pickling & Passivation: The tube blanks are subjected to acid pickling (HNO₃/HF blend) to remove scale and surface contaminants, followed by passivation to restore the chromium oxide passive film.
- Cold Coiling (Helical Forming): The straight tube is fed through a precision coiling machine equipped with a rotating mandrel and guide rollers. The tube is gradually bent into a helical shape at a controlled rate to avoid excessive work hardening, ovality, or wrinkling. CNC-controlled coiling ensures consistent helix diameter, pitch, and coil length.
- Stress Relief Annealing (Optional): For applications requiring dimensional stability, the coiled tubes may undergo a controlled annealing cycle (typically 1050°C – 1100°C followed by water quench) to relieve residual stresses introduced during cold forming. This step is critical for preventing spring-back and maintaining geometric precision.
- End Finishing: Tube ends are trimmed to precise lengths and finished according to specification—flared, threaded, or left plain. Brazing ends may be pre-tinned for field assembly.
- Final Cleaning & Surface Treatment: Electropolishing or mechanical polishing may be applied for sanitary or high-purity applications, achieving surface roughness values as low as Ra 0.2 μm.
- Quality Inspection & Testing: Comprehensive inspection including dimensional measurement (OD, WT, coil diameter, pitch), hydrostatic pressure testing, visual examination, and (where applicable) eddy current testing for wall integrity.
4.1 Key Manufacturing Considerations
- Ovality Control: The coiling process must be carefully controlled to limit ovality to ≤ 1.0% of the nominal OD, ensuring uniform wall thickness distribution around the coil cross-section.
- Work Hardening Management: Excessive cold work during coiling can reduce ductility and increase susceptibility to stress corrosion cracking. Process parameters are optimized to maintain adequate post-coiling elongation.
- Spring-Back Compensation: CNC coiling systems incorporate spring-back compensation algorithms to ensure the final coil geometry matches the design specification within tolerance.
5. Applications
The stainless steel spiral coil tube finds extensive use across multiple industrial sectors due to its compact geometry, superior heat transfer characteristics, and corrosion resistance:
5.1 Refrigeration & HVAC (Heating, Ventilation & Air Conditioning)
- Evaporator and condenser coils for commercial and industrial refrigeration systems
- Air conditioning heat exchangers and chiller units
- Freezer and cold storage refrigeration circuits
5.2 Chemical & Petrochemical Processing
- Compact heat exchangers and reactor cooling systems
- Process piping in corrosive chemical environments
- Distillation column condensers and reboilers
5.3 Food & Pharmaceutical Industry
- Sterilization systems (SIP/CIP — Sterilization/Cleaning In Place)
- Dairy processing heat exchangers (milk pasteurization, UHT treatment)
- Pharmaceutical fluid transfer and temperature control systems
5.4 Power Generation & Energy
- Turbine cooling circuits and steam generator tubes
- Solar thermal energy collectors (evacuated tube collectors)
- Geothermal heat exchange systems
5.5 Marine & Offshore
- Seawater cooling systems for ship engines and auxiliary equipment
- Offshore platform heat exchangers
5.6 Automotive & Transportation
- Radiator and intercooler cores
- Brake cooling systems for high-performance vehicles
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a rigorous quality management system to ensure product conformity and traceability:
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and delivery |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing practices |
| EN 10204 3.1 | Material Test Report (MTR) — independent third-party inspection available |
| ASME B31.3 | Process piping design code compliance |
| ASTM A269/A269M | Standard specification for seamless austenitic stainless steel tubing |
| NSF/ANSI 61 | Drinking water system components — material safety (available upon request) |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for EU market |
6.1 Inspection & Testing Protocols
- Hydrostatic Pressure Test: All coils are pressure-tested at 1.5× the maximum design pressure with a hold time of ≥ 30 seconds to verify weld integrity and wall soundness.
- Dimensional Inspection: 100% inspection of OD, wall thickness, coil diameter, and pitch using calibrated instruments (micrometers, calipers, laser gauges).
- Chemical Composition Analysis: OES (Optical Emission Spectroscopy) or wet chemical analysis for each heat number to verify elemental composition.
- Mechanical Testing: Tensile and hardness testing per ASTM A370 on representative samples from each production batch.
- Surface Quality: Visual and magnification inspection for surface defects, scratches, and contamination. Electropolished surfaces are verified by roughness profilometry.
- Intergranular Corrosion Test: ASTM A262 Practice E (for stabilized grades such as 321 and 310S) to verify resistance to intergranular attack.
7. Unique Selling Points
Enhanced Heat Transfer Performance: The helical geometry generates Dean vortices that promote turbulent mixing, delivering 20–40% higher heat transfer coefficients compared to straight tubes of equivalent diameter and length—enabling more compact heat exchanger designs.
- Precision CNC Coiling: Computer-controlled forming ensures consistent helix geometry with tight tolerances (±