Stainless Steel Coil Tube for Fan Coil Units (FCU)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: No. 1356
Classification: Technical Literature & Application Reference
1. Product Overview
Stainless steel coil tubes are precision-engineered continuous-length piping products, manufactured in coiled form for ease of transportation, storage, and on-site installation. These coil tubes serve as critical heat exchange elements in Fan Coil Units (FCU), which are integral components of modern HVAC (Heating, Ventilation, and Air Conditioning) systems. The coil tube design facilitates efficient thermal transfer between the circulating refrigerant or hot water medium and the ambient air stream, enabling precise temperature and humidity control within enclosed spaces.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the production of high-grade stainless steel coil tubes that meet the demanding requirements of variable air volume (VAV) operation modes in fan coil unit systems. The continuous coil configuration eliminates the need for field welding, significantly reducing installation time, minimizing leak points, and ensuring long-term system reliability.
2. Material & Properties
2.1 Base Materials
- Austenitic Stainless Steels: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 316L (UNS S31603) are the primary grades utilized for coil tube manufacturing.
- 304 Stainless Steel: Offers excellent general corrosion resistance, good formability, and is suitable for non-chloride environments in standard HVAC applications.
- 316 / 316L Stainless Steel: Contains 2–3% Molybdenum (Mo), providing superior resistance to pitting and crevice corrosion, particularly in environments with elevated chloride concentrations or aggressive chemical exposures.
2.2 Mechanical Properties
| Property | 304 Grade | 316 Grade |
|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 170 |
| Elongation (%) | ≥ 40 | ≥ 40 |
| Hardness (HB) | ≤ 217 | ≤ 217 |
| Thermal Conductivity (W/m·K, at 20°C) | 16.3 | 16.3 |
| Density (kg/m³) | 8,000 | 8,000 |
| Maximum Service Temperature (°C) | 870 | 870 |
2.3 Surface Finish Options
- Ba & No. 4 Finish: Standard commercial finish with a smooth, non-reflective appearance; suitable for most HVAC applications.
- Mirror Finish (8K): Highly polished surface with superior aesthetic quality; recommended for food-grade and pharmaceutical applications.
- Pickled & Passivated: Acid-removed surface with enhanced passive chromium oxide layer for maximum corrosion protection.
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.18 mm – 19.05 mm (1/8" – 3/4" NPS) |
| Wall Thickness | 0.30 mm – 2.11 mm (0.012" – 0.083") |
| Coil Length (Continuous) | Up to 500 m per coil (custom lengths available) |
| Coil Inner Diameter | 150 mm – 600 mm (standardized for pallet transport) |
| Dimensional Tolerance (OD) | ±0.05 mm (precision cold-drawn) |
| Dimensional Tolerance (Wall Thickness) | ±0.02 mm |
| Applicable Standards | ASTM A269, ASTM A270, GB/T 12771, EN 10217-7 |
| Pressure Rating | Up to 1.6 MPa (16 bar) working pressure (grade-dependent) |
| Operating Temperature Range | −196°C to +450°C (continuous) |
| End Condition | Plain cut, beveled, or custom-threaded |
4. Manufacturing Process
4.1 Process Flow
- Steel Mill Ingot Casting: Ultra-low carbon (ULC) stainless steel ingots are produced via vacuum arc remelting (VAR) or electro-slag remelting (ESR) to ensure exceptional purity and homogeneity.
- Hot Rolling & Annealing: Ingot material is hot-rolled into seamless tube blanks and solution-annealed to achieve the desired austenitic microstructure.
- Cold Drawing (Cold Reduction): The seamless tube blanks are cold-drawn through precision tungsten carbide (WC) dies to achieve exact dimensional tolerances, improved surface finish, and enhanced mechanical properties.
- Coiling: The cold-drawn tube is wound onto precision coil reels under controlled tension to maintain dimensional integrity and prevent kinking or ovality.
- Pickling & Passivation: The coiled tube undergoes hydrofluoric-nitric acid (HF-HNO₃) pickling to remove oxide scale, followed by passivation to restore the protective chromium oxide (Cr₂O₃) passive film.
- Quality Inspection: Each coil undergoes 100% ultrasonic testing (UT) for internal defects, hydrostatic pressure testing, dimensional verification, and chemical composition analysis via Optical Emission Spectroscopy (OES).
- Packaging & Dispatch: Coils are wrapped in moisture-resistant protective film, secured with steel strapping, and palletized for export or domestic distribution.
4.2 Key Manufacturing Advantages
- Continuous coil production eliminates butt-weld joints, reducing potential failure points by over 95% compared to cut-length pipe assemblies.
- Cold-drawing process achieves ±0.05 mm dimensional accuracy, ensuring precise fit with heat exchanger headers and terminal fittings.
- In-house pickling and passivation lines guarantee consistent surface quality and corrosion resistance across all production batches.
5. Applications
5.1 Fan Coil Unit (FCU) Systems
Stainless steel coil tubes are the primary heat exchange medium in fan coil units operating under Variable Air Volume (VAV) control strategies. The coil tube configuration enables:
- Efficient heat transfer between chilled water (typically 6–12°C) or hot water (45–60°C) and the air stream.
- Compact serpentine coil arrangements that maximize surface area within constrained unit footprints.
- Compatibility with modulating two-way and three-way control valves for precise thermal regulation.
- Resistance to scale formation and biofilm accumulation, maintaining long-term heat transfer efficiency.
5.2 Additional Application Domains
| Sector | Application Detail |
|---|---|
| Commercial HVAC | Ceiling-mounted and wall-mounted fan coil units in offices, hotels, and retail spaces |
| Industrial Process | Chilled water distribution, refrigerant lines, and process cooling circuits |
| Food & Beverage | Sanitary-grade piping in processing plants requiring CIP (Clean-in-Place) compatibility |
| Pharmaceutical | Cleanroom HVAC systems and GMP-compliant fluid handling |
| Marine & Offshore | Corrosion-resistant coil assemblies in high-salinity environments (316L grade) |
| Medical Facilities | Hospital HVAC systems requiring antimicrobial surface properties |
6. Quality Certifications & Standards Compliance
6.1 International Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent production quality.
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- CE Marking — Conformity with European Economic Area (EEA) health, safety, and environmental protection standards.
- EN 10204 3.1 — Inspection Certificate certifying conformity with specified requirements.
6.2 Product Standards
- ASTM A269 / A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service.
- ASTM A270 / A270M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing.
- GB/T 12771-2019 — Chinese National Standard for Stainless Steel Seamless Tubes for Fluid Transport.
- EN 10217-7:2018 — European Standard for Non-Alloy and Alloy Steel Tubes for Mechanical, Technical, and General Purposes.
- ASME B36.19M — Standard for Welded and Seamless Wrought Stainless Steel Pipe.
6.3 Testing & Inspection Protocols
| Test Method | Purpose | Standard Reference |
|---|---|---|
| Hydrostatic Pressure Test | Verify structural integrity and leak-tightness | ASTM A269 §10.6 |
| Ultrasonic Testing (UT) | Detect internal voids, laminations, and cracks | ASTM E1277 |
| Positive Material Identification (PMI) | Confirm alloy composition via XRF or OES | ASTM E1445 |
| Pitting Corrosion Test | Assess resistance to chloride-induced pitting | ASTM G48 |
| Tensile Testing | Verify mechanical properties meet specification | ASTM A370 |
| Surface Roughness Measurement | Confirm Ra value within specified range | ISO 4287 |
7. Unique Selling Points
Why Choose Wenzhou Jixing Metal Materials Co., Ltd. Stainless Steel Coil Tubes?
- Seamless Continuity: Continuous coil form eliminates field-weld joints, drastically reducing installation labor costs and potential leak points in FCU heat exchanger assemblies.
- Precision Cold-Drawn Tolerances: ±0.05 mm OD tolerance ensures plug-fit compatibility with standard header blocks and terminal fittings without reaming or deburring.
- Multi-Grade Flexibility: Availability in 304, 316, and 316L grades allows specification optimization based on environmental aggressiveness and budget constraints.
- Extended Service Life: Superior corrosion resistance compared to carbon steel alternatives extends system maintenance intervals by 3–5×, reducing total cost of ownership (TCO).
- Full Traceability: Each coil is accompanied by a mill test certificate (MTC) with heat number, chemical analysis, and mechanical test results, ensuring complete supply chain traceability.
- Custom Coiling: Coil lengths up to 500 m and customizable coil diameters accommodate diverse logistics and installation requirements.
8. Technical Literature Reference
This product specification is supplemented by the technical study document "Variable Air Volume Operation Mode of Fan Coil Units" (《风机盘管机组的变风量运行方式》), which provides in-depth analysis of how coil tube performance characteristics influence VAV system efficiency, control responsiveness, and thermal comfort. The study confirms that stainless steel coil tubes with high thermal conductivity and minimal fouling resistance are optimal for maintaining stable heat exchange coefficients under variable flow conditions, thereby supporting energy-efficient building operations in accordance with ASHRAE 90.1 and GB 50189 energy efficiency standards.