Stainless Steel Coil Tube — HVAC Series (Wenzhou Jixing Metal Materials Co., Ltd.)
1. Product Overview
The Stainless Steel Coil Tube (Product No. 1071) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing solution specifically designed for high-performance heating, ventilation, and air conditioning (HVAC) applications. This product is engineered to serve as the core heat-exchange element in both Dedicated Outdoor Air Systems (DOAS) and Fan Coil Units (FCUs), offering superior thermal transfer efficiency, long-term corrosion resistance, and mechanical reliability in demanding indoor climate-control environments.
Unlike conventional copper or carbon steel coil tubes, the stainless steel construction provides exceptional resistance to condensation-induced corrosion, chemical degradation from humid air streams, and mechanical fatigue under cyclic thermal loading — making it an ideal material choice for next-generation ventilation and air-handling systems.
2. Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected to optimize the balance between thermal conductivity, mechanical strength, and corrosion resistance in humid, chemically aggressive HVAC environments.
- Base Material: AISI 304 / AISI 316L Stainless Steel (austenitic grade)
- Chromium Content: 18–20% (minimum 18% for 304; 16–18% for 316L)
- Nickel Content: 8–12% (304); 10–14% (316L)
- Molybdenum Content: 2–3% (316L grade only, for enhanced chloride resistance)
- Carbon Content: ≤ 0.08% (304); ≤ 0.03% (316L — ultra-low carbon for welding stability)
- Thermal Conductivity: 14.9 W/(m·K) at 20°C (304); 13.2 W/(m·K) at 20°C (316L)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (304); 16.0 × 10⁻⁶ /K (316L)
- Yield Strength: ≥ 205 MPa (annealed condition)
- Tensile Strength: 515–720 MPa (304); 485–620 MPa (316L)
- Operating Temperature Range: −196°C to +870°C
- Surface Finish: 2B cold-rolled finish (Ra ≤ 0.4 μm) or electropolished (Ra ≤ 0.2 μm)
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | Φ8.0 mm / Φ9.53 mm (3/8") / Φ12.7 mm (1/2") / Φ15.88 mm (5/8") |
| Wall Thickness | 0.5 mm – 1.5 mm (selectable per application) |
| Coil Pitch (Turn-to-Turn Spacing) | 1.5 mm – 5.0 mm (adjustable for airflow optimization) |
| Coil Length | 100 mm – 2,500 mm (standard); custom lengths available |
| Coil Diameter | Φ150 mm – Φ600 mm |
| Number of Turns | 4 – 30 turns (configurable) |
| Tolerance on OD | ±0.05 mm (precision grade) |
| Tolerance on Wall Thickness | ±0.03 mm |
| Maximum Operating Pressure | 1.6 MPa (232 psi) at 20°C |
| Hydrostatic Test Pressure | 2.4 MPa (348 psi) — 1.5× working pressure |
| Maximum Working Fluid Temperature | +120°C (hot water); −20°C (chilled water) |
| Standard Length (per coil) | 3.0 m – 12.0 m (continuous coil) |
| Finish Options | Mill finish / Passivated / Electropolished / PTFE-coated (anti-condensation) |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip (coil) is sourced from certified mills and subjected to spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM A270 / EN 10216-5 standards.
- Slitting & Annealing: The master coil is precision-slitted to the required strip width. Interim solution annealing is performed at 1,050–1,100°C followed by controlled water quenching to restore full austenitic microstructure and eliminate cold-work hardening.
- Seamless Tube Forming (Roll-Bending): High-precision roll-bending equipment shapes the strip into a seamless tube with controlled wall thickness. Multi-roller stations ensure uniform curvature and minimal residual stress.
- Coil Forming (Spiral Coiling): The formed tube is passed through a programmable coiling head that precisely controls pitch, coil diameter, and turn count. CNC-controlled servos maintain dimensional tolerance within ±0.1 mm.
- Heat Treatment & Stress Relief: Post-forming stress-relief annealing at 450–550°C eliminates residual stresses introduced during cold coiling, preventing spring-back and distortion during service.
- Surface Treatment: Chemical passivation (citric acid or nitric acid bath) removes surface contaminants and establishes a protective chromium oxide layer. Electropolishing is applied for hygienic-grade applications.
- Quality Control & Testing: Each batch undergoes hydrostatic pressure testing, dimensional gauging (OD, wall thickness, pitch), visual inspection, and optional eddy-current testing (ECT) for subsurface defect detection.
- Packaging & Dispatch: Coils are wrapped in moisture-barrier film, crated, and labeled with traceability documentation including heat numbers, test certificates, and dimensional reports.
5. Applications
5.1 Dedicated Outdoor Air Systems (DOAS)
In Dedicated Outdoor Air Systems, the stainless steel coil tube serves as the primary heat-exchange element for conditioning 100% outdoor air. The corrosion-resistant properties of austenitic stainless steel make it particularly advantageous in environments where:
- High humidity levels cause persistent condensation on coil surfaces
- Outdoor air contains chlorides, pollutants, or acidic compounds
- Long service life (20+ years) is required without coil replacement
- Hygienic performance is critical (e.g., hospitals, laboratories, cleanrooms)
5.2 Fan Coil Units (FCU)
When integrated into Fan Coil Unit systems, the coil tube provides efficient sensible and latent heat transfer for space conditioning. The compact coil geometry maximizes surface-area-to-volume ratio, enabling high heat flux while maintaining low pressure drop across the coil bundle.
5.3 Additional Applications
- Chilled water distribution in commercial HVAC systems
- Condensing coils in air-to-water heat pump systems
- Process cooling in pharmaceutical and food-grade facilities
- Marine and coastal HVAC installations (316L grade)
- Refrigeration evaporator coils in cold storage
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring full traceability and regulatory compliance:
| Standard / Certification | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| EN 10216-5 | Welded austenitic stainless steel tubes for pressure purposes |
| ASTM A270 / A269 | Welded austenitic stainless steel tube specifications |
| GB/T 14975-2002 | Chinese national standard for seamless austenitic stainless steel tubes |
| TÜV / SGS Third-Party Testing | Independent material and performance verification |
| CE Marking | European conformity for pressure equipment (PED 2014/68/EU) |
| NSF/ANSI 61 | Drinking water system components (where applicable) |
7. Unique Selling Points
"Engineered for Lifetime Performance in the Harshest HVAC Environments"
- Exceptional Corrosion Resistance: The austenitic stainless steel matrix provides immunity to condensation corrosion, eliminating the common failure mode of carbon steel coils in humid HVAC applications.
- Hygienic Surface Integrity: Electropolished finish achieves Ra ≤ 0.2 μm, preventing microbial colonization and meeting pharmaceutical/food-grade sanitation requirements.
- Thermal Cycling Durability: Superior fatigue resistance under repeated heating/cooling cycles (100,000+ cycles verified) ensures dimensional stability over the equipment's entire service life.
- Reduced Total Cost of Ownership (TCO): Although initial material cost is higher than copper alternatives, the extended service life (2–3× longer), lower maintenance frequency, and elimination of replacement cycles deliver significant lifecycle savings.
- DOAS-Optimized Geometry: Coil pitch and turn configurations are specifically engineered to minimize pressure drop while maximizing heat transfer coefficient (U-value), directly improving system COP (Coefficient of Performance).
- Full Traceability: Every coil is traceable to its mill heat number, with complete chemical analysis, mechanical test data, and dimensional inspection reports provided per lot.
- Customization Capability: Flexible manufacturing parameters allow tailored OD, wall thickness, pitch, and coil geometry to match specific OEM requirements for both DOAS and FCU integrations.
8. Technical Notes & Recommendations
- Welding: Use GTAW (Gas Tungsten Arc Welding) or ORBT (Orbital Resistance Butt Welding) with argon shielding. Avoid SMAW to prevent chromium carbide precipitation at weld zones.
- Installation: Maintain minimum bend radius of 3× OD to prevent wall thinning or ovalization. Use spring-back compensation in bending fixtures.
- Water Quality: For 304 grade, limit chloride concentration to < 50 ppm. For 316L grade, safe up to 1,000 ppm chloride in non-crevice conditions.
- Storage: Store indoors or under protective cover. Avoid contact with carbon steel to prevent galvanic contamination and localized corrosion.
Document Reference: WJMM-SP-1071 | Rev. 2024 | Wenzhou Jixing Metal Materials Co., Ltd.