Stainless Steel Coil Tube — Precision Wound Fan Coil Unit Piping
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-wound tubular product engineered for use in fan coil unit (FCU) systems, HVAC (Heating, Ventilation, and Air Conditioning) applications, and industrial heat exchange environments. This coil tube is produced through a continuous cold-forming process that converts seamless or welded stainless steel tubing into a helical coil configuration, offering superior thermal conductivity, resistance to corrosion, and long-term structural integrity under cyclic thermal loading.
Based on extensive research into summer temperature and humidity control performance in fan coil unit rooms, this coil tube is optimized for dual-control (temperature and humidity) methodologies, ensuring stable and efficient operation in both cooling and heating modes. The product addresses the critical requirement for uniform heat transfer while minimizing pressure drop across the coil assembly.
2. Material & Properties
The coil tube is fabricated from austenitic stainless steel grades conforming to international metallurgical standards. The primary material specifications are as follows:
- Grade 304 (UNS S30400): General-purpose corrosion resistance with excellent weldability; suitable for ambient and moderate-temperature environments.
- Grade 316 (UNS S31600): Enhanced pitting and crevice corrosion resistance due to molybdenum (Mo) addition; recommended for aggressive chemical or marine environments.
- Grade 321 (UNS S32100): Titanium-stabilized grade for elevated-temperature service up to 870°C; prevents intergranular corrosion during welding.
Mechanical Properties (Annealed Condition)
| Property | Grade 304 | Grade 316 | Grade 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 485 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Thermal Conductivity (W/m·K at 100°C) | 16.3 | 14.6 | 16.3 |
| Linear Expansion Coefficient (10⁻⁶/K) | 17.3 | 16.0 | 17.3 |
Surface Finish Options
- No. 1 Annealed Finish (industrial standard)
- 2B Cold-Rolled and Annealed Finish
- No. 4 Brushed Finish
- Mirror Finish (No. 8) — available upon request
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.0 mm – 15.9 mm (custom sizes available) |
| Wall Thickness | 0.3 mm – 1.5 mm |
| Coil Pitch | 3.0 mm – 12.0 mm (adjustable per design requirement) |
| Coil Diameter | Up to 500 mm (standard); larger diameters available |
| Tube Length (Straight Section) | 6.0 m – 12.0 m (standard cut lengths) |
| Tolerance on OD | ± 0.05 mm |
| Tolerance on Wall Thickness | ± 10% of nominal |
| Pressure Rating | Up to 1.6 MPa (standard); up to 4.0 MPa (heavy-wall) |
| Operating Temperature Range | −196°C to +600°C (Grade 304/316); up to +870°C (Grade 321) |
| Winding Accuracy | ± 0.1 mm pitch deviation |
| End Treatment | Plain, beveled, or thread-forming (per customer specification) |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical soundness, and surface integrity:
- Raw Material Inspection: Incoming stainless steel wire or tube is verified for chemical composition (via Optical Emission Spectrometry — OES) and mechanical properties prior to processing.
- Cold Drawing / Forming: The parent tube is cold-drawn through precision-die tooling to achieve the target outer diameter and wall thickness with tight tolerances.
- Intermediate Annealing: Periodic solution annealing at 1050°C–1150°C with water quenching relieves cold-work hardening, restores ductility, and dissolves carbide precipitation for optimal corrosion resistance.
- Coil Winding: A CNC-controlled coiling machine winds the formed tube into a helical configuration with programmable pitch and coil diameter, ensuring uniform geometry throughout the length.
- Heat Treatment (if required): Final solution annealing and pickling/hydrofluoric acid descaling to remove oxide scale and restore passive chromium oxide film.
- Non-Destructive Testing (NDT): 100% eddy current testing (ECT) and/or ultrasonic testing (UT) of the tubing prior to coiling to detect internal and external defects.
- Final Dimensional Inspection: Optical measurement of OD, wall thickness, and coil pitch; visual surface inspection under controlled lighting.
- Packaging: Each coil is individually wrapped in moisture-proof protective film, secured with strapping, and labeled with heat number, grade, and dimensions for traceability.
5. Applications
- HVAC Systems: Primary application in fan coil units (FCU) for commercial and residential air conditioning; optimized for dual temperature-humidity control during summer cooling cycles.
- Heat Exchangers: Shell-and-tube and plate-fin heat exchanger assemblies in process industries.
- Refrigeration Systems: Evaporator and condenser coils in cold storage and industrial refrigeration.
- Chemical Processing: Piping and coil assemblies in corrosive chemical environments where carbon steel is unsuitable.
- Food and Pharmaceutical Industries: Sanitary-grade coil tubing for CIP (Clean-in-Place) compatible systems.
- Automotive Industry: Radiator core tubes and intercooler piping.
- Power Generation: Condenser tubes and feedwater heaters in thermal power plants.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring full traceability and conformance to international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- ISO/IEC 17025 — Laboratory Competence (in-house testing facility)
- ASTM A213 — Standard Specification for Seamless Ferritic Alloy Steel Tubing for High Temperature Service
- ASTM A269 — Standard Specification for Seamless and Wrought Stainless Steel Tubing, Austenitic
- EN 10217-7 — European Standard for Tubes for Heat Exchangers
- JIS G3459 — Japanese Industrial Standard for Stainless Steel Tubes
- ASME B36.19M — Instrument and Control Piping
- CE Marking — Conformity with European Pressure Equipment Directive (PED 2014/68/EU)
- TÜV / SGS Third-Party Inspection — Available upon customer request
7. Unique Selling Points
Precision Coil Geometry: CNC-controlled winding ensures ±0.1 mm pitch accuracy, guaranteeing optimal airflow distribution and thermal performance in fan coil unit applications.
- Enhanced Corrosion Resistance: Full solution-annealed and passivated finish provides a stable chromium oxide passive layer, extending service life in humid and chemically aggressive environments.
- Thermal Performance Optimization: Coil geometry is validated against CFD (Computational Fluid Dynamics) simulations to minimize pressure drop while maximizing heat transfer area.
- Full Traceability: Every coil is linked to its heat number, chemical analysis, and NDT records, enabling complete supply-chain traceability for critical applications.
- Custom Engineering Support: The manufacturer offers design consultation and custom coil configurations tailored to specific thermal load requirements, including dual-control temperature and humidity scenarios.
- Compliant with Dual-Control Research Findings: Product specifications are informed by academic research on summer temperature and humidity control in fan coil unit rooms, ensuring that the coil tube performs reliably under sustained cooling loads with precise humidity management.
8. Ordering Information & Technical Support
Customers are advised to provide the following parameters when placing an order:
- Required stainless steel grade (304, 316, 321, or custom)
- Target outer diameter and wall thickness
- Coil pitch and coil diameter
- Total length or number of turns required
- End treatment and surface finish preference
- Applicable standard or specification (ASTM, EN, JIS, etc.)
- Special requirements (NDT, material certificate EN 10204 3.1/3.2, third-party inspection)
Wenzhou Jixing Metal Materials Co., Ltd. provides technical data sheets, material certificates, and design assistance to ensure seamless integration of the coil tube into end-use systems.