Stainless Steel Coil Tube (Coiltube) for HVAC & Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Product No. 736) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, continuously wound tubular product designed for thermal exchange and fluid distribution systems. This coil tube is primarily deployed in Fan Coil Units (FCU), Hydronic Air Handling Systems, Chilled Water Loops, and Heat Recovery Systems where reliable heat transfer, corrosion resistance, and long-term operational integrity are paramount.
The coil tube is supplied in continuous coil form, enabling seamless integration into automated manufacturing lines and minimizing material waste during fabrication. Its helical wound geometry provides a high surface-area-to-volume ratio, making it exceptionally efficient for convective and conductive heat exchange applications.
Material & Properties
Base Material
- Primary Alloy Grade: AISI 304 / ASTM A269 TP304 (18% Cr – 8% Ni austenitic stainless steel)
- Alternative Grades: AISI 316 / ASTM A269 TP316 (with 2–3% Molybdenum for enhanced chloride resistance); AISI 321 / TP321 (Ti-stabilized for high-temperature service)
- Material Form: Cold-rolled stainless steel strip, precision-rolled into seamless coil tubing
Mechanical Properties (Typical for Grade 304)
- Tensile Strength: ≥ 520 MPa (75,400 psi)
- Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Hardness (HB): 140 – 210
Physical & Thermal Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Specific Heat Capacity: 500 J/(kg·K) at 20°C
- Linear Thermal Expansion: 17.3 × 10⁻⁶ /°C (20–100°C)
- Density: 8.0 g/cm³
- Operating Temperature Range: −196°C to +870°C (Grade 304); −196°C to +850°C (Grade 316)
Corrosion Resistance
- Excellent resistance to atmospheric, acidic, and alkaline environments
- Immune to uniform corrosion in most aqueous and gaseous media
- Grade 316 variant provides superior resistance to pitting and crevice corrosion in chloride-rich environments (e.g., coastal or chemical processing applications)
- Passive chromium oxide film (Cr₂O₃) self-heals in oxidizing environments, ensuring long-term surface integrity
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Code | 736 – Coiltube | Internal Catalog |
| Outer Diameter (OD) | 6.35 mm / 8.00 mm / 9.53 mm / 12.70 mm (¼″ / ⅜″ / ⅜″ / ½″ nominal) | ASTM A269 / EN 10217 |
| Wall Thickness | 0.50 mm – 1.50 mm (adjustable per customer requirement) | ASTM A269 |
| Coil Inner Diameter | 300 mm – 600 mm | Manufacturing Standard |
| Coil Length (Continuous) | 10 m – 200 m per coil (customizable) | — |
| Surface Finish | Ba & Bright Annealed (2B); No. 4 Brushed; Mirror Polish (Ra ≤ 0.2 μm) | ASTM A480 |
| Tolerance on OD | ±0.05 mm (Precision Grade); ±0.10 mm (Standard Grade) | ISO 6508 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Strut Size (for FCU Coil) | Standard: 25.4 mm (1″); Custom: 12.7 mm – 50.8 mm | ASHRAE 15 / AHRI 210/240 |
| Maximum Operating Pressure | 1.6 MPa (232 psi) standard; 2.5 MPa (363 psi) pressure-tested | EN 10217-2 |
| Hydrostatic Test Pressure | 3.0 MPa (435 psi) minimum | ASME B31.9 |
| Coating / Surface Treatment | Pickled & Passivated; Optional PTFE or Epoxy Internal Coating | ASTM A967 |
| End Treatment | Plain ends; Welded; Threaded (BSPP/BSPT/NPT); Flanged (ASME B16.5) | — |
Manufacturing Process
1. Raw Material Preparation
High-purity stainless steel strip (Grade 304/316/321) is sourced from certified mills and subjected to incoming inspection including chemical composition analysis (spectroscopy), mechanical property verification, and surface defect examination.
2. Precision Roll Forming
The flat strip is fed through a multi-station roll forming die set, where progressive rollers incrementally bend the strip into the desired circular cross-section. This cold-forming process ensures dimensional accuracy, eliminates seams, and maintains the metallurgical integrity of the material without heat-affected zones.
3. Continuous Welding (where applicable)
For seamless coil tubing, the roll-forming process produces a fully welded tube. For welded variants, a high-frequency resistance welding (HFRW) or laser welding process is employed to produce a tight, metallurgically sound longitudinal weld. Weld quality is verified through radiographic testing (RT) or ultrasonic testing (UT).
4. Heat Treatment & Annealing
Coil tubes are subjected to a Ba & Bright Annealing process at 1050–1150°C in a controlled atmosphere (nitrogen or vacuum), followed by rapid cooling. This eliminates residual stresses, restores ductility, and produces a clean, oxide-free surface suitable for direct service without additional cleaning.
5. Pickling & Passivation
The annealed coils undergo a pickling cycle using a mixed acid solution (nitric + hydrofluoric acid) to remove any residual scale, followed by passivation with a citric or nitric acid bath. This establishes a stable, protective chromium oxide passive film (per ASTM A967), critical for long-term corrosion resistance.
6. Coiling & Packaging
The finished coil tube is wound onto precision steel cores and wrapped with protective paper or PE film. Each coil is labeled with product identification, heat number, and traceability data.
7. Quality Control & Testing
- Dimensional Inspection: OD, wall thickness, and coil diameter verified using micrometers, ultrasonic gauges, and laser measurement systems
- Hydrostatic Pressure Testing: 100% of production tested at 3.0 MPa minimum for 10 seconds hold time
- Chemical Analysis: Spectrometric verification of Cr, Ni, Mo, C, Si, Mn content per ASTM A269
- Mechanical Testing: Tensile and elongation tests per ASTM A269/A270
- Surface Inspection: Visual and magnetic particle inspection for cracks, seams, and surface defects
- Corrosion Testing: Salt spray testing (ASTM B117) — minimum 1000 hours without pitting for Grade 316 variants
Applications
1. Fan Coil Units (FCU) — Primary Application
The coil tube serves as the core heat exchanger element in fan coil units used in commercial and residential HVAC systems. The continuous coil configuration maximizes the heat transfer surface area within a compact footprint, enabling efficient cooling and heating of air streams. The stainless steel material provides:
- Resistance to condensation-induced corrosion (a common failure mode in aluminum coils)
- Elimination of galvanic corrosion in mixed-metal heat exchanger assemblies
- Long service life (20+ years) even under aggressive humidity and temperature cycling conditions
- Prevention of the centralized control burnout accident scenario documented in industry literature, where degraded coil performance leads to excessive thermal loads on control circuits and subsequent electrical failure
2. Chilled Water & Hot Water Heating Systems
Used in commercial building HVAC systems, district heating networks, and process cooling applications where fluid temperatures range from 0°C to 95°C and corrosion resistance is critical.
3. Refrigeration & Air Conditioning
Evaporator and condenser coils in commercial refrigeration units, cold storage facilities, and industrial process chillers. Stainless steel coil tubes withstand low-temperature operation (down to −40°C) without embrittlement.
4. Industrial Heat Exchangers
Shell-and-tube heat exchangers, plate-and-fin assemblies, and process heating/cooling systems in chemical, pharmaceutical, and food processing industries where sanitary and corrosion-resistant materials are mandated.
5. Solar Thermal & Geothermal Systems
Heat collection coils in solar water heating systems and geothermal heat pump applications where long-term durability and resistance to thermal cycling are essential.
6. Medical & Laboratory Equipment
Temperature-controlled chambers, autoclaves, and analytical instruments requiring hygienic, non-reactive heat transfer surfaces.
Quality Certifications
| Certification / Standard | Description | Status |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Certified |
| ISO 14001:2015 | Environmental Management System | Certified |
| ISO 45001:2018 | Occupational Health & Safety Management System | Certified |
| CE Marking | European Conformity — compliance with EU directives for pressure equipment and machinery | Certified |
| EN 10217-2 | European standard for stainless steel welded tubes for pressure purposes | Compliant |
| ASTM A269 / A270 | American standard for austenitic stainless steel seamless and welded tubing | Compliant |
| GB/T 12771 (China) | Chinese national standard for stainless steel welded tubes for general purposes | Compliant |
| ASME B31.9 | Pressure Piping — Refrigeration and Air-Conditioning | Compliant |
| RoHS / REACH | Restriction of Hazardous Substances / Registration, Evaluation, Authorisation and Restriction of Chemicals | Compliant |
Unique Selling Points
- Superior Corrosion Resistance vs. Copper and Aluminum Coils: Stainless steel coil tubes eliminate the risk of electrochemical corrosion in mixed-fluid environments, extending system life by 3–5× compared to conventional copper-tube aluminum-fin (CU-ALF) heat exchangers.
- Prevention of Centralized Control Burnout: By maintaining consistent thermal performance over the product lifecycle, these coil tubes prevent the thermal degradation cascades that lead to FCU control board burnout — a documented failure mode in aging HVAC installations.
- Continuous Coil Form Factor: Delivered in continuous coil configuration, enabling automated, high-speed fabrication into heat exchanger coils with minimal material waste and reduced labor costs.
- Full Traceability: Each coil is heat-numbered and traceable to mill certifications, ensuring complete supply chain transparency and compliance with regulatory requirements.
- Wide Range of Configurations: Available in multiple alloy grades, diameters, wall thicknesses, and surface finishes to accommodate diverse application requirements from residential HVAC to industrial process systems.
- Sustainable & Recyclable: 100% recyclable material with low embodied energy, supporting green building certifications (LEED, BREEAM) and circular economy objectives.
Technical Notes & Recommendations
Installation Advisory: During fabrication of FCU coils from coil tube stock