Stainless Steel Coil Tube — Fan Coil Unit Heat Exchanger Tube
Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for use in Fan Coil Units (FCUs), air handling systems, and HVAC (Heating, Ventilation, and Air Conditioning) heat exchangers. These coil tubes serve as the core heat transfer medium in both chilled water and hot water distribution systems, enabling efficient thermal energy exchange between the circulating fluid and the surrounding air stream.
Unlike conventional straight-segment tubing, coil tubes are formed into continuous helical or serpentine geometries that maximize the surface-area-to-volume ratio, thereby enhancing convective and conductive heat transfer performance within compact heat exchanger envelopes. This product is engineered to meet the rigorous demands of commercial, residential, and industrial ventilation systems, including office buildings, hospitals, data centers, and manufacturing facilities.
Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, mechanical strength, thermal conductivity, and long-term dimensional stability under cyclic thermal loading.
- Base Material: AISI 304 (UNS S30408) / AISI 316L (UNS S31603) austenitic stainless steel
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, condensation water, and mild chemical environments encountered in HVAC systems
- Chromium Content (Cr): 18–20 wt% (AISI 304); 16–18 wt% (AISI 316L)
- Nickel Content (Ni): 8–10 wt% (AISI 304); 10–14 wt% (AISI 316L)
- Molybdenum Content (Mo): ≤0.08% (AISI 304); 2–3 wt% (AISI 316L, enhanced pitting resistance)
- Operating Temperature Range: −196°C to +870°C (AISI 304); −196°C to +870°C (AISI 316L)
- Thermal Conductivity: 14–16 W/(m·K) at 20°C
- Yield Strength: ≥205 MPa (AISI 304); ≥170 MPa (AISI 316L)
- Tensile Strength: ≥515 MPa (AISI 304); ≥485 MPa (AISI 316L)
- Surface Finish: No. 1 (annealed), No. 4 (brushed), or 2B (cold rolled and annealed) — selected per application requirement
- Non-magnetic: Practically non-magnetic in the annealed condition (austenitic structure)
Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | Φ6.35 mm, Φ8.00 mm, Φ9.53 mm, Φ12.70 mm, Φ15.88 mm, Φ19.05 mm | ±0.05 mm |
| Wall Thickness (WT) | 0.50 mm, 0.71 mm, 0.81 mm, 1.00 mm, 1.20 mm | ±0.03 mm |
| Coil Pitch (P) | 8 mm – 25 mm (customizable) | ±0.5 mm |
| Coil Diameter (CD) | 300 mm – 1200 mm (customizable) | ±1.0 mm |
| Tube Length (Uncoiled) | 3 m – 50 m (standard); up to 100 m (special order) | ±50 mm |
| Material Grade | AISI 304 / AISI 316L / Custom alloy | — |
| End Forming | Plain end / Flared / Soldered / Brazed / Threaded | Per drawing |
| Maximum Working Pressure | ≤1.6 MPa (standard); ≤2.5 MPa (reinforced) | Per ASME B31.9 |
| Hydrostatic Test Pressure | 1.5× working pressure | — |
| Surface Roughness (Ra) | ≤0.8 μm (internal); ≤1.6 μm (external) | — |
| Standard Reference | ASTM A213 / ASTM A269 / GB/T 12771 / EN 10217-7 | — |
Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a multi-stage precision manufacturing workflow designed to ensure geometric accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tubing is sourced from certified mills, with chemical composition verified via Optical Emission Spectroscopy (OES) and Positive Material Identification (PMI) testing.
- Coil Forming (Tube Bending): Continuous tube bending machines with CNC (Computer Numerical Control) guidance form the straight tube into the specified helical or serpentine coil geometry. The bending process employs multi-axis roller systems to prevent wall thinning, ovalization, and material work-hardening at bend radii. The minimum bend radius is maintained at ≥3× the tube OD to preserve structural integrity.
- Heat Treatment (if required): Post-forming stress relief annealing is performed at 1050°C – 1150°C in a protective atmosphere (argon or vacuum) to restore the fully annealed austenitic microstructure, relieve residual stresses introduced during cold forming, and ensure consistent mechanical properties throughout the coil.
- Pickling & Passivation: The formed coil tubes undergo acid pickling (HNO₃/HF blend) to remove oxide scale and surface contaminants, followed by passivation treatment to form a protective chromium oxide (Cr₂O₃) film on the surface, enhancing corrosion resistance.
- Dimensional Inspection: Each batch is inspected for OD, wall thickness, coil pitch, and coil diameter using laser micrometers, ultrasonic thickness gauges, and coordinate measurement machines (CMM). Internal bore inspection is performed via borescope where applicable.
- Pressure Testing: Every coil tube undergoes a hydrostatic pressure test at 1.5× the maximum working pressure, held for a minimum of 60 seconds with zero leakage permitted. Pneumatic testing is available as an alternative for specific applications.
- End Finishing: Tube ends are trimmed, deburred, and formed to specification (flared, threaded, or prepared for brazing/soldering) using precision end-forming equipment.
- Packaging & Dispatch: Tubes are individually wrapped in moisture-proof polyethylene film, bundled in protective crates or wooden cases, and labeled with traceable batch numbers and material certificates.
Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. are widely deployed across multiple industries and system types:
- Commercial HVAC Systems: Fan Coil Units (FCUs) for office buildings, hotels, hospitals, and shopping malls — the primary application domain. The coil tube serves as the heat transfer element in both cooling (chilled water) and heating (hot water) modes.
- Fresh Air Handling Systems: Integrated with fresh air supply and ventilation units (新风系统), where coil tubes provide sensible and latent heat treatment of incoming outdoor air to achieve precise indoor climate control.
- Industrial Process Cooling/Heating: Precision temperature control in semiconductor fabrication, pharmaceutical manufacturing, food processing, and chemical plants.
- Refrigeration & Cryogenic Systems: Heat exchangers in medium-temperature refrigeration, cold storage, and cryogenic applications where corrosion resistance and low-temperature ductility are critical.
- Automotive & Transportation: Auxiliary heat exchangers in electric vehicles (EV), train air conditioning systems, and marine HVAC installations.
- Residential Heating & Cooling: Compact coil tube assemblies in ductless mini-split systems and radiant floor heating manifolds.
- Water Heating Systems: Immersion-type and plate-type water heater heat exchangers requiring long service life in aggressive water environments.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that all stainless steel coil tube products meet or exceed international standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- EN 10204 3.1 — Material Test Certificate (third-party inspection) provided with each shipment
- ASTM A213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-temperature Service
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Other General Purposes
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes
- ASME B31.9 — Pressure Piping, Refrigeration Piping and Heat Transfer Components
- RoHS / REACH Compliance — Restriction of Hazardous Substances / Registration, Evaluation, Authorisation and Restriction of Chemicals (EU directive compliance)
- Mill Test Reports (MTR) — Full chemical and mechanical property documentation traceable to the heat number
Unique Selling Points
Wenzhou Jixing Metal Materials Co., Ltd. distinguishes its stainless steel coil tube offerings through the following competitive advantages:
- Precision Geometry Control: CNC-driven coil forming technology ensures coil pitch and diameter tolerances of ±0.5 mm and ±1.0 mm respectively — significantly tighter than industry averages — resulting in superior heat exchanger packing density and airflow uniformity.
- Customized Coil Configurations: Full flexibility in OD, wall thickness, pitch, coil diameter, and total length to accommodate OEM-specific fan coil unit designs and proprietary heat exchanger architectures.
- Enhanced Corrosion Durability: The use of AISI 316L grade with molybdenum (Mo) addition provides superior resistance to chloride-induced pitting and crevice corrosion, extending service life in coastal, humid, and chemically aggressive environments.
- Full Traceability: Each coil tube batch is traceable from raw material mill certificate through every manufacturing stage, with digital quality records available upon request — critical for regulated industries such as pharmaceuticals and food processing.
- Optimized for HVAC Performance: Internal surface roughness maintained at Ra ≤ 0.8 μm minimizes fluid-side pressure drop while maximizing heat transfer coefficient, contributing to improved COP (Coefficient of Performance) in fan coil unit applications.
- Integrated Fresh Air System Compatibility: Coil tube designs specifically engineered for fresh air handling unit (PAU — Primary Air Unit) integration, enabling simultaneous sensible and latent heat removal with optimized air distribution patterns in commercial ventilation systems.
- Competitive Lead Times: Standard configurations available from stock within 5–7 business days; custom orders delivered within 15–25 business days, supported by a vertically integrated supply chain.
- Sustainable Manufacturing: ISO 14001-certified environmental practices, including recycled stainless steel sourcing options, waste minimization protocols, and energy-efficient forming processes that reduce the carbon footprint of each product.
Technical Notes for System Integration
When integrating these stainless steel coil tubes into Fan Coil Unit and Fresh Air System assemblies, the following engineering considerations should be observed:
- Welding/Brazing Compatibility: Use of silver-bearing brazing alloys (e.g., BAg-8) or TIG (Tungsten Inert Gas) welding with matching filler wire (ER308L for AISI 304; ER316L for AISI 316L) to maintain intergranular corrosion resistance at joints.
- Flow Rate Optimization: Internal coil geometry influences pressure drop (ΔP) and flow distribution; CFD (Computational Fluid Dynamics) analysis is recommended for system-level optimization, particularly in multi-row coil configurations.
- Condensate Management: In cooling applications, proper slope (≥1:100) and condensate drainage provisions must be designed around the coil tube assembly to prevent waterlogging and microbial growth.
- Thermal Cycling Fatigue: The austenitic microstructure provides excellent fatigue resistance under repeated heating and cooling cycles, but proper expansion loop design should be incorporated in long piping runs to accommodate differential thermal expansion.
For detailed engineering drawings, material certificates, and technical consultation regarding custom coil tube specifications, please contact Wenzhou Jixing Metal Materials Co., Ltd. — a trusted manufacturer and supplier of precision stainless steel tubing products for the global HVAC and industrial heat exchange markets.