Stainless Steel Coil Tube for Fan Coil Units — Technical Specification
Product Overview
The Stainless Steel Coil Tube (also referred to as Coil Tubing or Coiltube) is a precision-engineered product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is primarily designed for integration into Fan Coil Units (FCUs), which serve as terminal air conditioning devices in commercial, industrial, and residential HVAC (Heating, Ventilation, and Air Conditioning) systems. The coil tube functions as the core heat exchange element, facilitating efficient thermal transfer between the circulating fluid (water or refrigerant) and the ambient air stream.
Unlike conventional straight-tube heat exchangers, the coil tube configuration offers a significantly larger surface-area-to-volume ratio, enabling superior thermal performance within compact installation envelopes. This product line adheres to internationally recognized standards including ASTM (American Society for Testing and Materials), EN (European Norms), and GB (Chinese National Standards) for stainless steel tubing applications.
Material & Properties
The coil tube is fabricated from high-grade Stainless Steel alloys, selected for their exceptional corrosion resistance, thermal conductivity, and mechanical durability. The primary material grades utilized include:
- 304 Stainless Steel (AISI 304 / 1.4301) — The most widely specified grade, offering excellent general corrosion resistance, formability, and weldability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- 316 Stainless Steel (AISI 316 / 1.4401) — Enhanced resistance to pitting and crevice corrosion due to the addition of 2–3% Molybdenum (Mo), making it suitable for aggressive chemical environments.
- 316L Stainless Steel (AISI 316L / 1.4404) — Low-carbon variant of 316 grade, optimized for welding applications with reduced sensitization risk.
Key Material Properties:
- Corrosion Resistance: Superior resistance to atmospheric, aqueous, and chemical corrosion; passive oxide layer (Cr₂O₃) self-repairs in the presence of oxygen.
- Thermal Conductivity: Approximately 14–16 W/(m·K) for austenitic grades, providing reliable heat transfer performance.
- Operating Temperature Range: From cryogenic temperatures (−196°C / −320°F) to approximately 870°C (1,598°F) in oxidizing atmospheres.
- Mechanical Strength: Tensile strength typically ranging from 515–750 MPa (75,000–109,000 psi) depending on grade and condition.
- Hygienic Surface Finish: Available in electropolished (Ra ≤ 0.5 μm) or passivated finishes to minimize fouling and bacterial adhesion.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (¼" – 1") | ASTM A269 / A270 |
| Wall Thickness | 0.5 mm – 2.0 mm (0.020" – 0.079") | ASTM A269 / A270 |
| Coil Diameter (Bundling) | 100 mm – 500 mm (4" – 20") | Manufacturer Specification |
| Coil Length | Up to 100 meters (328 ft) per continuous coil | Manufacturer Specification |
| Material Grade | 304, 316, 316L, 321, 347 | ASTM / EN / GB |
| Surface Finish | Pickled & Passivated, Electropolished, Brushed | ASTM A967 |
| Tolerance on OD | ±0.05 mm (±0.002") | ASTM A213 |
| Pressure Rating | Up to 1.6 MPa (232 psi) working pressure | EN 12828 / GB 50015 |
| Operating Fluid | Water, Glycol Solutions, Refrigerants, Steam | Manufacturer Specification |
| Welding Method | TIG (GTAW), Resistance Welding, Brazing | ASTM A240 |
| Standard Lengths | Custom coil lengths; straight cut lengths available upon request | — |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip (CRSS) conforming to ASTM A240 / EN 10088 is sourced from certified mills. Incoming material undergoes spectroscopic verification (PMI — Positive Material Identification) to confirm chemical composition.
- Forming & Coiling: The strip is fed through precision roll-forming equipment to achieve the target outer diameter and wall thickness. Continuous coiling is performed on calibrated mandrels to ensure uniform curvature and prevent work hardening.
- Welding (for welded tube): High-frequency induction welding (HFW) or laser welding is employed to form the longitudinal seam. Weld quality is verified via ultrasonic testing (UT) and visual inspection (VT).
- Heat Treatment: Solution annealing is conducted at 1010–1150°C (1,850–2,092°F) followed by rapid water quenching to restore full austenitic structure and maximize corrosion resistance.
- Pickling & Passivation: The coil is treated in nitric-hydrofluoric acid (HNO₃–HF) solution to remove mill scale, oxide layers, and residual contaminants, followed by passivation to establish a stable chromium oxide protective film.
- Dimensional Inspection: Automated optical systems measure OD, wall thickness, and coil diameter at intervals not exceeding every 5 meters. Samples undergo destructive testing including tensile testing (ASTM A370) and hardness testing (ASTM E92).
- Performance Testing: Coil tubes are subjected to hydrostatic pressure testing at 1.5× the maximum working pressure for a minimum dwell time of 30 minutes to verify leak-tightness and structural integrity.
- Coiling & Packaging: Finished coils are wound on protective spools, wrapped in moisture-barrier film, and palletized for shipment with accompanying mill test certificates (MTC) per EN 10204 Type 3.1.
Applications
The stainless steel coil tube is integral to a wide range of thermal management and fluid handling applications:
- Fan Coil Units (FCUs): Primary application as the heat exchange coil within air handling terminals for commercial buildings, hospitals, data centers, and cleanrooms. The coil tube's geometry maximizes air-side and fluid-side heat transfer coefficients.
- Chilled Water Systems: Circulating chilled water (typically 6–12°C / 43–54°F) through the coil tube to cool and dehumidify supply air.
- Hot Water Heating: Hot water (45–80°C / 113–176°F) circulation for space heating in cold-climate installations.
- Refrigerant Systems: Direct expansion (DX) coil applications where refrigerant evaporates within the tube, transferring latent heat to the airstream.
- Process Cooling: Industrial heat exchangers for chemical processing, food and beverage production, and pharmaceutical manufacturing where hygienic and corrosion-resistant tubing is mandated.
- Domestic Hot Water (DHW): Coil tubes embedded in storage tank walls for indirect water heating via hydronic loops.
Performance Testing Methodology for Fan Coil Units
Based on established engineering research and industry practice regarding fan coil unit performance testing, the following methodology is recommended for evaluating the thermal and hydraulic performance of coil tubes integrated into FCUs:
- Air-Side Testing: Conducted in accordance with ANSI/ASHRAE Standard 34 and EN 1395. The unit is tested under controlled air inlet conditions (dry-bulb and wet-bulb temperatures), with measurement of total air flow rate (CFM), inlet/outlet air temperatures, and static pressure drop across the coil.
- Fluid-Side Testing: Water flow rate is measured via calibrated magnetic flow meters; inlet and outlet water temperatures are recorded using thermocouples (Type T or K) with accuracy of ±0.1°C. The heat transfer rate (Q) is calculated as: Q = m × Cp × ΔT, where m is the mass flow rate, Cp is the specific heat capacity, and ΔT is the temperature difference.
- Performance Metrics: Sensible Heat Ratio (SHR), Total Cooling Capacity (W or BTU/hr), EER (Energy Efficiency Ratio), and Air-Side Heat Transfer Coefficient (hA) are derived from test data.
- Hydraulic Characterization: Pressure drop (ΔP) across the coil is measured as a function of flow rate to generate the hydraulic performance curve, enabling proper pump selection and system design.
Engineering Note: The thermal performance of the coil tube within an FCU is influenced by factors including fin density (fins per inch — FPI), tube layout (in-line vs. staggered), air velocity, and fouling factor. A fouling factor of 0.0001–0.0002 m²·K/W is typically assumed for clean water service in design calculations.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality assurance systems and holds the following certifications and compliance accreditations:
- 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 — European Conformity for pressure equipment and construction products
- EN 10204 Type 3.1 — Mill Test Certificates with full chemical and mechanical property data
- NSF/ANSI 61 — Drinking Water System Components (for potable water applications)
- GB/T 12459 — Chinese National Standard for seamless and welded stainless steel pipe fittings
- PED 2014/68/EU — Pressure Equipment Directive compliance for pressure-rated assemblies
Each production batch undergoes traceability through a unique heat number and coil identifier. Full material traceability from raw steel mill to finished coil is maintained, ensuring complete supply chain accountability.
Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel grades provide a service life exceeding 25 years in typical HVAC applications without degradation of thermal performance.
- Hygienic Design: Electropolished surface finishes with Ra ≤ 0.5 μm prevent microbial colonization, making the product suitable for pharmaceutical and food-grade applications.
- Thermal Efficiency: Optimized coil geometry with precise fin-tube bonding (expand-fit or mechanical crimp) minimizes thermal contact resistance.
- Custom Engineering: Capability to manufacture to customer-specific dimensional requirements, including custom coil diameters, tube counts, and circuit configurations.
- Full Traceability: Each coil is accompanied by a comprehensive test certificate enabling verification of chemical composition, mechanical properties, and dimensional compliance.
Wenzhou Jixing Metal Materials Co., Ltd is committed to delivering precision-engineered stainless steel coil tube solutions that meet the most demanding performance, durability, and quality standards in the global HVAC and industrial thermal management markets.