Stainless Steel Coil Tube (Coiltube) — Industrial Fan Coil Unit Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered product designed primarily for the FWY-600 Type Fan Coil Unit with Residual Pressure (FWY-600型带余压风机盘管) and similar HVAC (Heating, Ventilation, and Air Conditioning) systems. This coil tube series is fabricated from high-grade austenitic stainless steel, offering superior corrosion resistance, thermal conductivity, and mechanical durability. The product is classified under industrial-grade coil tubing (盘管) and is widely recognized for its application in hydronic heat exchange systems, where consistent fluid flow and reliable heat transfer performance are critical.
The coil tube design incorporates a residual pressure (余压) configuration, which ensures stable pressure distribution across the coil matrix even under variable flow conditions. This engineering feature is particularly significant in large-scale commercial HVAC installations where maintaining uniform thermal output is essential for energy efficiency and occupant comfort.
Material & Properties
The coil tube is constructed from premium austenitic stainless steel, typically conforming to the following material specifications:
- Primary Alloy Grades: SUS304 (UNS S30400), SUS316 (UNS S31600), and SUS304L (UNS S30403)
- Chromium (Cr) Content: 18.0–20.0% (provides primary corrosion resistance)
- Nickel (Ni) Content: 8.0–12.0% (ensures austenitic microstructure stability)
- Molybdenum (Mo) Content: 2.0–3.0% (in SUS316 grade; enhances pitting resistance)
- Carbon (C) Content: ≤0.08% (standard) / ≤0.03% (L-grade; minimizes sensitization risk)
- Operating Temperature Range: −196°C to +870°C
- Thermal Conductivity: 14–16 W/(m·K) at 20°C
- Specific Heat Capacity: 500 J/(kg·K) at 25°C
- Density: 7.93 g/cm³
- Yield Strength (Rp0.2): ≥205 MPa (annealed condition)
- Tensile Strength (Rm): ≥520 MPa
- Elongation (A50mm): ≥40%
The austenitic microstructure provides excellent formability, weldability, and non-magnetic properties. The passive chromium oxide layer (Cr₂O₃) self-repairs in the presence of oxygen, providing sustained protection against oxidation and corrosion in aggressive chemical environments.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (盘管 / Coiltube) | — |
| Model Reference | FWY-600 Series Compatible | Enterprise Standard (Q/WZJX) |
| Tube Outer Diameter (OD) | 7.0 mm / 8.0 mm / 9.52 mm / 10.0 mm | ASTM A269 / ASTM B482 |
| Tube Wall Thickness | 0.50 mm – 1.20 mm (customizable) | ISO 11733 |
| Coil Pitch (Center-to-Center) | 15 mm – 30 mm (configurable) | Enterprise Standard |
| Coil Length (Developed) | 3,000 mm – 12,000 mm (per unit) | Custom per application |
| Fin Material | Aluminum (1100-H14) or Stainless Steel (SUS304) | ASTM B209 / ASTM A240 |
| Fin Thickness | 0.10 mm – 0.15 mm | — |
| Fin Spacing (FPI) | 12 – 18 fins per inch | ASHRAE 15 |
| Design Pressure | 1.0 MPa – 2.5 MPa (operating); 1.5× (test) | EN 12828 / GB 50241 |
| Heat Transfer Capacity | Up to 12,000 W (sensible + latent) | ASHRAE Standard 40 |
| Flow Rate | 0.4 – 3.5 m³/h (water side) | — |
| Surface Treatment | Pickled & Passivated (P&P); optional electropolishing | ASTM A967 / ASTM B934 |
| Connection Type | Threaded (G1/2", G3/4", G1") / Flanged / Welded | ISO 7-1 / GB/T 7306 |
| Residual Pressure Rating | 0.1 – 0.5 kPa (maintained across coil matrix) | Enterprise Standard |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, surface integrity, and mechanical performance:
- Raw Material Selection & Incoming Inspection: Stainless steel coil stock is sourced from certified mills and subjected to spectrographic analysis (OES — Optical Emission Spectroscopy) to verify alloy composition. Each batch undergoes visual inspection for surface defects, including pitting, scratches, and oxide scale.
- Slitting & Straightening: The coil stock is slit to the required tube blank width using precision slitting lines. Straightening is performed to achieve a flatness tolerance of ≤0.5 mm/m.
- Forming & Seaming: The flat blanks are formed into tubular sections using a roll-forming process. The longitudinal seam is welded using TIG (Tungsten Inert Gas) welding or high-frequency resistance welding (HFRW) with full internal and external seam inspection via eddy current testing (ECT) or X-ray radiography.
- Coil Winding & Pitch Control: The formed tubes are wound into coil configurations using CNC-controlled winding machines. Pitch accuracy is maintained within ±0.5 mm tolerance through servo-driven motor control systems.
- Fin Attachment: Aluminum or stainless steel fins are applied via a stamping and clinching process or brazing (for copper-aluminum variants). The fin-tube interface is inspected for bond integrity.
- Heat Treatment (if required): Solution annealing at 1050–1150°C followed by rapid water quenching may be applied to restore full annealed mechanical properties and enhance corrosion resistance.
- Pickling & Passivation: The finished coil tube assembly is treated with a mixed acid solution (HNO₃ + HF) to remove mill scale and welding discoloration, followed by passivation to establish a uniform chromium oxide protective layer.
- Pressure & Leak Testing: Each unit undergoes hydrostatic pressure testing at 1.5× the design pressure for a minimum dwell time of 15 minutes. Leak detection is verified using helium mass spectrometry or soap bubble testing for critical applications.
- Final Dimensional Inspection: Coordinate measuring machine (CMM) inspection verifies OD, wall thickness, coil length, pitch uniformity, and overall dimensional conformity.
Applications
The stainless steel coil tube is engineered for demanding thermal management applications across multiple industries:
- HVAC Systems: Primary application in fan coil units (FCUs), including the FWY-600 residual pressure series, for commercial buildings, hospitals, laboratories, and cleanroom environments.
- Chemical Processing: Heat exchangers and condensers in chemical plants where resistance to aggressive media (acids, chlorides, caustics) is essential.
- Food & Beverage Industry: Pasteurization, sterilization, and cooling systems where sanitary-grade (3-A) compliance and corrosion resistance are mandatory.
- Pharmaceutical Manufacturing: GMP-compliant thermal processing equipment requiring non-reactive, easily cleanable surfaces.
- Marine & Offshore: Seawater-cooled heat exchangers and condensers where chloride-induced pitting and crevice corrosion are prevalent.
- Power Generation: Condensers, feedwater heaters, and economizers in thermal and nuclear power plants.
- Refrigeration & Cryogenics: Evaporators and condensers operating at low temperatures where ductile fracture resistance is critical.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management infrastructure to ensure product reliability and regulatory compliance:
- ISO 9001:2015 — Quality Management Systems (QMS)
- ISO 14001:2015 — Environmental Management Systems (EMS)
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- CE Marking — Conformity with European Union directives (PED 2014/68/EU for pressure equipment)
- EN 10204 — Material Test Certificates (Type 2.1 or 3.1 available upon request)
- ASTM International Standards Compliance: A269, B482, A967, B934, A240
- ASME Standards Compliance: BPE (Boiler and Pressure Vessel) where applicable
- GB National Standards (China): GB/T 12771, GB/T 4237, GB 50241
- NSF/ANSI 61 — Drinking Water System Components (for potable water applications)
- 3-A Sanitary Standards — Food, Dairy, and Beverage Processing Equipment
Unique Selling Points (USPs)
1. Residual Pressure Stabilization Technology: The FWY-600 series coil tube incorporates a proprietary residual pressure design that maintains consistent pressure distribution across the entire coil matrix, eliminating flow maldistribution and ensuring uniform heat transfer performance under variable load conditions.
2. Superior Corrosion Resistance: The use of SUS316-grade stainless steel with 2–3% molybdenum provides exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC) in chloride-rich environments — a significant advantage over carbon steel and copper alternatives.
3. Precision Manufacturing: CNC-controlled winding and forming processes deliver dimensional accuracy within ±0.3 mm tolerance, ensuring optimal fin-tube contact and maximum heat transfer efficiency.
4. Full Traceability: Every coil tube unit is traceable from raw material mill certificate through final inspection, with digital batch records maintained for quality assurance and warranty purposes.
5. Customization Capability: Flexible configuration options for tube OD, wall thickness, coil pitch, fin density, and connection types allow tailored solutions for specific application requirements.
6. Extended Service Life: With proper installation and maintenance, the stainless steel coil tube offers a service life exceeding 25 years — substantially outperforming copper-tube alternatives in corrosive environments.
Technical Notes & Recommendations
- Welding Compatibility: Use ER308L or ER316L filler wire for TIG welding; preheat temperatures should not exceed 150°C to avoid sensitization. Post-weld passivation is strongly recommended.
- Installation: Avoid contact with dissimilar metals (carbon steel, copper) to prevent galvanic corrosion. Use stainless steel isolation gaskets where mixed-material connections are unavoidable.
- Storage: Store in a dry, well-ventilated environment. Protect from contact with chlorides, ammonia, and acidic substances. Wrap in protective film during transport.
- Maintenance: Periodic inspection of the passive layer is recommended in aggressive environments. Re-passivation may be required annually in marine or chemical processing applications.