Stainless Steel Coil Tube for Fan Coil Unit Systems
Product Overview
The stainless steel coil tube (盘管 / Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular component designed for integration into fan coil unit (FCU) and fresh air system (FAS) assemblies. As a critical heat exchange element, this coil tube serves as the primary medium for thermal energy transfer between circulating coolant/heating fluid and the indoor air stream, directly influencing the system's capacity to regulate indoor relative humidity (IRH) and temperature. The product is engineered to meet rigorous performance standards required in commercial HVAC (Heating, Ventilation, and Air Conditioning) applications where consistent humidity control is paramount.
The coil tube is supplied in continuous coiled form, facilitating seamless installation into fan coil unit evaporator and condenser sections without the need for field welding or additional joint fabrication, thereby minimizing potential leak points and enhancing long-term system reliability.
Material & Properties
The coil tube is fabricated from austenitic stainless steel, predominantly conforming to the following material grades:
- 304 Stainless Steel (UNS S30400) — The standard grade offering excellent corrosion resistance, formability, and weldability suitable for general HVAC applications.
- 316 Stainless Steel (UNS S31600) — Enhanced grade with added molybdenum (Mo) content, providing superior resistance to chlorides and aggressive chemical environments, recommended for coastal or high-humidity installations.
- 321 Stainless Steel (UNS S32100) — Titanium-stabilized variant for applications requiring resistance to intergranular corrosion at elevated temperatures.
Key material properties include:
- Thermal Conductivity: 14–16 W/(m·K), ensuring efficient heat transfer across the tube wall.
- Corrosion Resistance: Passivation layer formation in oxidizing environments; resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC).
- Mechanical Strength: Tensile strength ≥ 520 MPa; yield strength ≥ 205 MPa; elongation ≥ 40%.
- Operating Temperature Range: −196 °C to +870 °C, accommodating both chiller and hot-water heating circuits.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Category | Stainless Steel Coil Tube (盘管) | — |
| Outer Diameter (OD) | 6.35 mm, 9.53 mm, 12.70 mm (1/4", 3/8", 1/2") | ASTM A778 / ASTM A269 |
| Wall Thickness | 0.50 mm – 1.00 mm | ASTM A778 |
| Coil Winding Diameter | 100 mm – 500 mm (configurable per application) | Custom / OEM |
| Coil Length (per piece) | 15 m – 100 m (configurable) | — |
| Surface Finish | 2B (cold-rolled, annealed, pickled) | ASTM A480 |
| End Condition | Plain ends or pre-flared for brazing | — |
| Heat Exchange Efficiency | U-value ≥ 180 W/(m²·K) (typical for FCU coil assembly) | ASHRAE 40.1 |
| Design Pressure | ≥ 1.6 MPa (16 bar) | EN 12161 / ASHRAE 15 |
| Material Grade Options | 304 / 316 / 321 Stainless Steel | ASTM A269 / ASTM A778 |
| Maximum Operating Temperature | +120 °C (water circuit); +870 °C (material limit) | — |
| Corrosion Resistance | Passivation verified per ASTM A967 | ASTM A967 |
Manufacturing Process
The production of the stainless steel coil tube follows a multi-stage precision manufacturing workflow:
- Hot-Rolled Billet Preparation — Virgin stainless steel ingots or recycled scrap are melted in AOD (Argon Oxygen Decarburization) or VOD (Vacuum Oxygen Decarburization) furnaces to achieve precise chemical composition control.
- Hot Rolling & Annealing — The billet is hot-rolled into seamless tube blanks, followed by solution annealing at 1050–1100 °C to restore full austenitic microstructure.
- Pickling & Descaling — The tube surface is treated with nitric-hydrofluoric acid mixtures to remove oxide scales, followed by thorough rinsing and passivation per ASTM A967.
- Cold Drawing & Sizing — The tube is cold-drawn through precision dies to achieve exact outer diameter and wall thickness tolerances (±0.05 mm), improving surface finish to 2B grade.
- Coil Winding — The straight tube is wound onto a CNC-controlled coiling machine to produce uniform helical coils with consistent pitch and winding diameter, suitable for direct insertion into fan coil unit heat exchanger frames.
- Hydrostatic Pressure Testing — Each coil lot undergoes 100% hydrostatic testing at 1.5× the design pressure (typically 2.4 MPa) to verify weld integrity and wall uniformity.
- Final Inspection & Packaging — Dimensional verification, surface inspection, and material certification documentation are completed before packaging in moisture-proof reels with protective end caps.
Applications
The stainless steel coil tube is integral to the following end-use applications:
- Fan Coil Units (FCU) — Primary application domain. The coil tube forms the core of FCU evaporator/condenser sections, enabling precise indoor air temperature and relative humidity control. The analysis referenced in the product documentation highlights the critical role of coil design in maintaining indoor relative humidity (IRH) within the comfort range of 40–60% RH when integrated with a dedicated fresh air supply system.
- Fresh Air Systems (FAS) — Pre-conditioning coils in dedicated outdoor air systems (DOAS) for humidity control prior to air distribution.
- Commercial HVAC Systems — Office buildings, hotels, hospitals, and retail spaces requiring zoned comfort control.
- Residential HVAC — Ducted split systems and cassette units in high-end residential installations.
- Industrial Process Cooling — Temperature-sensitive manufacturing environments requiring corrosion-resistant heat exchange media.
- Marine & Coastal HVAC — 316-grade coil tubes for installations exposed to salt-laden air.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification covering design, manufacturing, and delivery processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ASTM A269 / A778 Compliance — Material and product conformance to American Society for Testing and Materials standards for seamless and welded austenitic stainless steel tube.
- EN 10217-7 — European standard for seamless stainless steel tubes for technical applications.
- ASME BPV Section VIII — Pressure vessel code compliance for coil assemblies used in pressurized HVAC circuits.
- CE Marking — Conformity with European machinery and pressure equipment directives (PED 2014/68/EU).
- Mill Test Certificates (MTC) — EN 10204 3.1 certificates provided with each shipment, documenting chemical composition, mechanical properties, and heat treatment records.
Unique Selling Points
- Superior Humidity Control Performance — The high thermal conductivity and precise dimensional tolerances of the coil tube enable efficient dehumidification and humidification cycles, directly supporting the indoor relative humidity control capabilities validated in fan coil unit plus fresh air system analyses.
- Corrosion-Free Longevity — Austenitic stainless steel construction eliminates the risk of internal tube corrosion and scale buildup that plagues copper and carbon steel alternatives, extending service life beyond 25 years under normal operating conditions.
- Hygienic Surface Finish — The 2B passivated surface resists microbial adhesion and biofilm formation, making it suitable for healthcare and pharmaceutical HVAC applications where indoor air quality (IAQ) is critical.
- Field Installation Efficiency — Pre-wound coil geometry eliminates on-site tube bending and reduces installation time by up to 60% compared to straight-tube configurations requiring field fabrication.
- Full Traceability — Each coil batch is traceable to its heat number, mill certificate, and pressure test record, ensuring complete supply chain transparency for project audits and warranty claims.
Note: The technical analysis referenced in the product documentation — "Analysis of Indoor Relative Humidity Control Capability of Fan Coil Unit Plus Fresh Air System" — provides empirical validation of the coil tube's role in achieving target indoor relative humidity setpoints. The study demonstrates that coil tube geometry (pitch, diameter, and row count) is a dominant factor in latent heat removal efficiency, underscoring the importance of precision manufacturing tolerances in this product line.