Stainless Steel Coil Tube (Coiltube) — HVAC Heat Exchanger Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Series: No. 765 — Precision Coil Tube for Fan Coil Unit (FCU) and Thermal Management Systems
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component designed primarily for use in Heating, Ventilation, and Air Conditioning (HVAC) systems, particularly in Fan Coil Units (FCU) and dry-type air handling systems with independent fresh air supply. These coil tubes serve as the core heat exchange elements, facilitating efficient thermal transfer between the working fluid (water, refrigerant, or glycol solution) and the surrounding air stream.
Wenzhou Jixing Metal Materials Co., Ltd. manufactures coil tubes to meet the demanding requirements of modern building climate control, industrial process cooling, and commercial refrigeration systems. The product is engineered to provide superior thermal conductivity, exceptional corrosion resistance, and long-term mechanical integrity under cyclic thermal loading conditions.
2. Material & Properties
2.1 Base Alloy Designation
The coil tube is fabricated from Stainless Steel conforming to international alloy specifications, with primary grades including:
- AISI 304 / UNS S30408: General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- AISI 316 / UNS S31603: Enhanced molybdenum-bearing grade for aggressive environments (chloride-rich or chemical exposure).
- AISI 316L / UNS S31603L: Low-carbon variant for superior weldability and resistance to intergranular corrosion.
2.2 Chemical Composition (Typical — Grade 304)
| Element | Specification (%) | Element | Specification (%) |
|---|---|---|---|
| Carbon (C) | ≤ 0.08 | Nickel (Ni) | 8.00 – 10.50 |
| Chromium (Cr) | 18.00 – 20.00 | Manganese (Mn) | ≤ 2.00 |
| Molybdenum (Mo) | — (or ≤ 0.10) | Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 | Iron (Fe) | Balance |
2.3 Mechanical Properties (Cold-Wrought Condition)
- Tensile Strength (UTS): ≥ 520 MPa (75,400 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation (in 50 mm gauge length): ≥ 40%
- Hardness (Brinell): ≤ 217 HB
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
2.4 Corrosion Resistance Characteristics
The passive chromium oxide film (Cr₂O₃) formed on the tube surface provides outstanding resistance to atmospheric corrosion, oxidizing acids, and aqueous environments. Grade 316 variants offer additional pitting and crevice corrosion resistance in chloride-containing solutions, making them suitable for coastal installations and chemical processing environments.
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 9.52 mm (3/8") / 12.70 mm (1/2") / 15.88 mm (5/8") / Custom |
| Wall Thickness | 0.50 mm – 1.50 mm (tolerance ±10%) |
| Coil Diameter | 100 mm – 500 mm (configurable) |
| Coil Pitch (Center-to-Center Spacing) | 25.4 mm – 50.8 mm (1" – 2") |
| Tube Length (per circuit) | 1.0 m – 6.0 m (customizable) |
| Surface Finish | Mirror Polish (Ra ≤ 0.2 μm) / Brushed / Pickled & Passivated |
| Operating Temperature Range | −196°C to +450°C |
| Maximum Operating Pressure | ≤ 1.6 MPa (232 psi) — standard; up to 4.0 MPa for heavy-wall |
| End Forming | Plain / Flanged / Soldered / Brazed / Crimped |
| Applicable Standards | ASTM A269, ASTM A213, EN 10216-5, GB/T 12771 |
| Coil Configuration | Spiral / Helical / Serpentine / U-Tube Loop |
| Fin Configuration (if finned) | Integral Latch Fin / Soldered Aluminum Fin / Brazed Fin |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Selection & Inspection: Certified stainless steel coil stock is received with mill test certificates (MTC) and subjected to incoming quality verification including spectroscopic composition analysis and visual inspection.
- Slitting & Leveling: The parent coil is slit to precise tube width and leveled to eliminate residual stress and ensure flatness prior to forming.
- Tube Forming (Rolling): Precision roll-forming equipment shapes the flat strip into a seamless tubular cross-section with controlled wall thickness uniformity.
- Welding (if applicable): Longitudinal seams (if present) are welded using Tungsten Inert Gas (TIG) welding or Orbital Welding under inert atmosphere protection to maintain interior surface quality.
- Coil Winding / Spinning: The formed tube is wound into the designated coil geometry using CNC-controlled coil winding machines to ensure consistent pitch, concentricity, and dimensional accuracy.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050°C – 1150°C followed by rapid water quench to dissolve carbides and restore full austenitic structure.
- Pickling & Passivation: Surface scale and oxide are removed via acid pickling (nitric-hydrofluoric acid blend), followed by passivation to re-establish the protective chromium oxide layer.
- Surface Finishing: Final surface treatment includes mechanical polishing or electropolishing to achieve the required surface roughness (Ra value).
- Quality Control & Testing: Dimensional verification, hydrostatic pressure testing, visual inspection, and optional endoscopy of interior surfaces.
- Packaging & Dispatch: Coils are wrapped in protective film, placed on wooden pallets, and secured for transport.
4.2 Key Process Parameters
- Forming Reduction Ratio: Optimized to maintain ductility while achieving target wall thickness (typically 15%–35% reduction).
- Winding Tension Control: CNC-monitored to prevent coil collapse or inter-layer contact damage.
- Weld Quality: Weld penetration verified by radiographic testing (RT) or ultrasonic testing (UT) per ASTM E747.
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCU): Integral heat exchange coils in commercial and residential air conditioning systems, including dry-type FCU configurations with independent fresh air supply.
- Air Handling Units (AHU): Chilled water coils and heating coils for large-scale HVAC systems in commercial buildings, hospitals, and cleanrooms.
- Chilled Beam Systems: Radiant cooling and heating applications in premium commercial spaces.
- Industrial Process Cooling: Heat exchangers in chemical processing, pharmaceutical manufacturing, and food processing.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration and cold storage facilities.
5.2 Specialized Applications
- Cleanroom HVAC: Low-particle-emission coil tubes for semiconductor fabrication and pharmaceutical environments.
- Marine & Offshore Systems: Corrosion-resistant heat exchange coils for shipboard HVAC and offshore platform climate control.
- Data Center Cooling: High-efficiency coils for precision air conditioning in server rooms and telecommunications infrastructure.
- Renewable Energy Systems: Heat recovery units in solar thermal and geothermal applications.
5.3 Airflow Organization Compatibility
Research on dry-type fan coil units with independent fresh air systems has demonstrated that coil tube geometry and pitch significantly influence airflow organization (air distribution pattern) within the conditioned space. Optimal coil tube configurations ensure uniform air discharge velocity, minimize short-circuiting of supply air, and achieve efficient mixing with room air. Wenzhou Jixing's precision coil tube manufacturing ensures consistent geometric parameters that support predictable and optimized airflow performance in such systems.
6. Quality Certifications & Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- CE Marking — European Conformity for construction products
- ASME B31.9 — Refrigeration and Air-Conditioning Pressure Piping (where applicable)
6.2 Material & Test Certifications
- Mill Test Certificate (MTC / EN 10204 3.1): Chemical composition and mechanical property verification for each heat lot.
- Hydrostatic Pressure Test: All coils tested per ASTM A269 at 1.5× working pressure with zero leakage tolerance.
- Non-Destructive Testing (NDT): Visual testing (VT), dye penetrant testing (PT), and ultrasonic testing (UT) for weld integrity.
- Dimensional Inspection: 100% dimensional verification of OD, wall thickness, coil pitch, and total length.
- Corrosion Testing: Salt spray testing per ASTM B117 (≥ 1000 hours without red rust for Grade 316).
6.3 Applicable Standards & Codes
| Standard | Description |
|---|---|
| ASTM A269 / A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing |
| ASTM A213 | Standard Specification for Austenitic Chromium-Nickel Stainless Steel Seamless Tubes for High-temperature Service |
| EN 10216-5 | Non-alloy and stainless steel heat-exchanger tubes and condenser tubes — Technical delivery conditions |
| GB/T 12771 | Chinese National Standard — Welded Stainless Steel Tubes for General Purposes |
| GB/T 17887 | Chinese National Standard — Welded Stainless Steel Tubes for Heat Exchangers |
| ASHRAE Standard 15 | Standard for Safety Standards for Refrigeration Systems |
7. Unique Selling Points
- Precision Geometry: CNC-controlled coil winding ensures ±0.5 mm tolerance on pitch and concentricity, critical for uniform airflow distribution in FCU systems.
- Superior Corrosion Resistance: Full austenitic stainless steel construction eliminates internal corrosion, extending service life to 20+ years even in humid or chemically aggressive environments.
- High Thermal Efficiency: Optimized wall thickness and surface finish minimize thermal resistance, achieving heat transfer coefficients exceeding 80 W/(m²·K) for water-air applications.
- Hygienic Design: Mirror-polished interior surfaces (Ra ≤ 0.2 μm) prevent biofilm formation, making these coils suitable for pharmaceutical, food-grade, and cleanroom applications.
- Custom