Stainless Steel Coil Tube — Fan Coil Unit (FCU) Heat Exchanger Series
Product Overview
The Stainless Steel Coil Tube (FCU Series) is a precision-engineered, continuous wound stainless steel tube designed specifically for use in Fan Coil Unit (FCU) and fresh air system heat exchangers. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product represents the company's advanced capability in producing seamless stainless steel coil tubes optimized for HVAC (Heating, Ventilation, and Air Conditioning) thermal transfer applications. The coil tube is engineered to withstand the demanding cyclic thermal and mechanical conditions encountered during winter air treatment processes in commercial and industrial ventilation systems.
Unlike conventional straight tubes, the coil tube is supplied in a continuous helical or spiral configuration, eliminating the need for post-fabrication bending operations. This design reduces manufacturing waste, ensures uniform wall thickness throughout the coil, and significantly improves the overall thermal efficiency of the heat exchanger core. The product is particularly suited for applications requiring high corrosion resistance, long service life, and reliable performance under continuous operation conditions.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of mechanical strength, corrosion resistance, and thermal conductivity. The primary material grades include:
- SAE 304 (UNS S30400) — General-purpose grade with excellent corrosion resistance in most atmospheric and aqueous environments; suitable for standard HVAC applications.
- SAE 316 (UNS S31600) — Enhanced molybdenum (Mo 2.0–3.0%) content provides superior resistance to pitting and crevice corrosion; recommended for applications involving humid or chemically aggressive environments.
- SAE 316L (UNS S31603) — Low-carbon variant of 316 grade, optimized for post-welding applications where sensitization resistance is critical.
Key Mechanical and Physical Properties
| Property | SAE 304 | SAE 316 / 316L |
|---|---|---|
| Tensile Strength (Ultimate) | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ≥ 170 MPa |
| Elongation (at Break) | ≥ 40% | ≥ 40% |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | 16.6 × 10⁻⁶ /°C |
| Density | 8.00 g/cm³ | 8.03 g/cm³ |
| Maximum Service Temperature | 870°C | 870°C |
| Minimum Service Temperature | −196°C (Cryogenic) | −196°C (Cryogenic) |
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (FCU Series) |
| Material Grade | SAE 304 / 316 / 316L |
| Outer Diameter (OD) | 6.35 mm – 25.4 mm (¼" – 1") |
| Wall Thickness | 0.50 mm – 2.00 mm |
| Coil Diameter (Winding Diameter) | 150 mm – 500 mm |
| Coil Length (per Spool) | 20 m – 100 m (customizable) |
| Surface Finish | No. 4 Brushed / BA (Bright Annealed) / 2B |
| Surface Roughness (Ra) | ≤ 0.8 μm (BA finish); ≤ 1.6 μm (2B finish) |
| Dimensional Tolerance (OD) | ±0.05 mm (Precision); ±0.10 mm (Standard) |
| Dimensional Tolerance (Wall) | ±0.05 mm (Precision); ±0.10 mm (Standard) |
| Pressure Test | Hydrostatic test at 2.0 × working pressure |
| Operating Pressure | Up to 1.6 MPa (standard); up to 2.5 MPa (custom) |
| Operating Temperature Range | −40°C to +150°C (FCU typical) |
| Winding Pitch | Adjustable per heat exchanger core design |
| Packaging | Wooden pallet / export-grade carton with moisture barrier |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Inspection — Incoming stainless steel strip is verified for chemical composition (via Spectroscopy), mechanical properties, and surface condition in accordance with ASTM A240 / EN 10088 standards.
- Coil Winding — The stainless steel strip is wound around a precision-mandrel system using CNC-controlled equipment to achieve consistent coil diameter, uniform pitch, and minimal distortion. The winding process maintains metallurgical stress within acceptable limits to prevent spring-back or deformation.
- Solid-State Brazing / Welding (if applicable) — For multi-pass coil configurations, adjacent tube layers are joined using phosphorus-based brazing or orbital TIG welding to ensure leak-tight interlayer connections.
- Heat Treatment (Annealing) — The wound coil undergoes solution annealing at 1050–1100°C followed by rapid water quenching to restore full austenitic microstructure, relieve residual stresses, and achieve maximum corrosion resistance and ductility.
- Pickling and Passivation — The annealed coil is subjected to acid pickling (HNO₃/HF blend) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide (Cr₂O₃) protective film on the surface.
- Surface Finishing — Depending on the specified finish grade, the coil undergoes mechanical polishing (No. 4) or chemical bright annealing (BA) in a vacuum or inert-atmosphere furnace.
- Dimensional Inspection — Each coil spool is inspected using laser micrometers, ultrasonic wall thickness gauges, and optical comparators to verify OD, wall thickness, coil diameter, and overall length.
- Pressure Testing — Each finished coil assembly undergoes hydrostatic pressure testing at 2.0× the maximum rated working pressure to confirm leak integrity.
- Packaging and Dispatch — Qualified coils are packaged on export-grade wooden pallets with VCI (Vapor Corrosion Inhibitor) wrapping and moisture barrier protection for safe international shipment.
Applications
The Stainless Steel Coil Tube (FCU Series) finds extensive application in the following domains:
- Fan Coil Unit (FCU) Systems — Primary application; the coil tube forms the core heat exchanger element in FCU units used for space heating, cooling, and dehumidification in commercial buildings, hospitals, hotels, and office complexes.
- Fresh Air Handling Systems — Used in air handling units (AHUs) and make-up air systems where corrosion-resistant heat exchangers are required for winter air treatment and humidification processes.
- Commercial HVAC Systems — Chilled water and hot water coil assemblies in large-scale ventilation and air conditioning installations.
- Food Processing Equipment — Sanitary-grade heat exchangers in dairy, beverage, and pharmaceutical processing lines where material purity and cleanability are paramount.
- Marine and Offshore HVAC — Corrosion-resistant coil tubes for air conditioning systems on ships, offshore platforms, and coastal facilities exposed to salt-laden environments.
- Industrial Process Cooling — Precision temperature control applications in manufacturing environments requiring reliable, long-life heat transfer components.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all products meet or exceed international standards:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and quality assurance processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- CE Marking — Conformity with European Union safety, health, and environmental protection requirements.
- ASTM Compliance — Product specifications conform to ASTM A240 (Stainless Steel Plate/Sheet/Strip), ASTM A213 (Welded Austenitic Stainless Steel Tubing), and ASTM B730 (Welded Austenitic Stainless Steel Coil).
- EN Standards Compliance — Products meet EN 10088 (Stainless Steels) and EN 10217 (Heat-resistant, high-temperature, and pressure tubes) European standards.
- Mill Test Reports (MTR) — Each production batch is accompanied by a full material test report including chemical analysis (PMI), mechanical test results, and dimensional inspection data.
- Third-Party Inspection — Available upon customer request; products can be inspected by SGS, BV, or TÜV prior to shipment.
Unique Selling Points
Continuous Coil Configuration — Pre-wound coil design eliminates post-manufacturing bending operations, reducing distortion risk and ensuring consistent thermal performance across the entire heat exchanger surface.
- Enhanced Corrosion Resistance — 316/316L grades with 2–3% Molybdenum provide exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking, extending service life to 20+ years in demanding environments.
- Precision Winding Accuracy — CNC-controlled winding ensures coil diameter tolerance within ±1.0 mm and pitch uniformity within ±0.5 mm, enabling seamless integration into automated heat exchanger assembly lines.
- Optimized Thermal Performance — Smooth BA or No. 4 surface finish minimizes fouling resistance and maximizes heat transfer coefficients, contributing to overall system energy efficiency improvements of 8–15% compared to standard finish alternatives.
- Full Traceability — Each coil spool is serialized with heat number, material grade, and production batch information, enabling complete supply chain traceability and quality assurance documentation.
- Customization Capability — Flexible production capacity allows customization of OD, wall thickness, coil diameter, length, surface finish, and material grade to meet specific customer engineering requirements.
Wenzhou Jixing Metal Materials Co., Ltd. — A trusted supplier of premium stainless steel coil tubes for global HVAC and industrial heat exchange applications, combining advanced manufacturing technology with rigorous quality control to deliver reliable, high-performance thermal components.