Stainless Steel Coil Tube — Fan Coil Unit Application Grade

Product Overview

The Stainless Steel Coil Tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product designed primarily for use in Fan Coil Units (FCUs) within commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) systems. These coil tubes serve as the core heat exchange element, facilitating efficient thermal transfer between the circulating medium (water or refrigerant) and the surrounding air stream. The product is engineered to address typical operational challenges encountered in fan coil unit applications, including thermal efficiency degradation, corrosion resistance under prolonged exposure, and mechanical fatigue under continuous vibration loads.

This coil tube product represents a solution to common field issues such as uneven heat distribution, scale formation, and structural deformation that plague inferior coil tube designs. By leveraging high-grade stainless steel alloys and advanced cold-drawing manufacturing techniques, Wenzhou Jixing delivers a product that ensures extended service life, superior thermal conductivity, and reliable performance under demanding operating conditions.

Material & Properties

The coil tubes are fabricated from premium austenitic stainless steel grades, selected for their exceptional combination of corrosion resistance, thermal stability, and mechanical integrity. The following table summarizes the key material properties:

Property Specification Test Method / Standard
Material Grade 304 (UNS S30400) / 316L (UNS S31603) Austenitic Stainless Steel ASTM A213 / ASTM A269
Chromium (Cr) Content 18.0% – 20.0% (304) / 16.0% – 18.0% (316L) ASTM E415
Nickel (Ni) Content 8.0% – 10.5% (304) / 10.0% – 14.0% (316L) ASTM E415
Molybdenum (Mo) Content — (304) / 2.0% – 3.0% (316L) ASTM E415
Tensile Strength ≥ 515 MPa (75 ksi) ASTM A370
Yield Strength ≥ 205 MPa (29.7 ksi) ASTM A370
Elongation at Break ≥ 40% ASTM A370
Thermal Conductivity (at 20°C) 16.3 W/(m·K) (304) / 14.6 W/(m·K) (316L) ASTM E1461
Corrosion Resistance Superior to carbon steel; 316L grade offers enhanced resistance to chlorides and acidic environments ASTM A967 (Pickling Test)
Operating Temperature Range −196°C to +870°C Manufacturer Data
Surface Finish 2B (Cold Rolled Annealed) or Polished (Ra ≤ 0.4 μm) ASTM A480

Specifications

The following table details the dimensional and performance specifications for the standard product range:

Parameter Specification Remark
Outer Diameter (OD) 6.0 mm / 8.0 mm / 9.53 mm (3/8") / 12.7 mm (1/2") Custom sizes available upon request
Wall Thickness (WT) 0.5 mm / 0.8 mm / 1.0 mm / 1.2 mm Tolerance: ±0.05 mm
Coil Diameter (CD) 50 mm / 75 mm / 100 mm / 150 mm / 200 mm Custom winding radii available
Tube Length (Uncoiled) 2 m – 12 m (standard); up to 25 m (special order) Continuous coil or cut-to-length
Coil Weight 50 kg – 300 kg per coil Based on configuration
Number of Rows 1-row / 2-row / 3-row / 4-row configurations For FCU heat exchanger assemblies
Fin Pitch (if finned) 2.0 mm / 2.5 mm / 3.0 mm / 3.5 mm Available with aluminum fins
Pressure Rating Up to 1.6 MPa (16 bar) at 20°C; 1.0 MPa at 90°C Hydrostatic test: 1.5× working pressure
Surface Tolerance ±0.02 mm (diameter); ±0.5 mm (straightness per meter) Per ASTM A213
Standards Compliance ASTM A213, ASTM A269, EN 10216-5, GB/T 12771 Multi-standard certification

Manufacturing Process

The production of Wenzhou Jixing's stainless steel coil tubes follows a rigorous, multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:

  1. Raw Material Selection and Incoming Inspection: Hot-rolled stainless steel strips are sourced from certified mills and subjected to spectroscopic analysis (ASTM E415) to verify chemical composition. Each batch is accompanied by a Mill Test Certificate (MTC) in accordance with EN 10204 Type 3.1.
  2. Pickling and Passivation: The raw strips undergo acid pickling (per ASTM A967) to remove surface oxides, followed by passivation treatment to establish a protective chromium oxide layer. This step is critical for ensuring long-term corrosion resistance in HVAC applications.
  3. Cold Drawing and Forming: The strips are cold-drawn through precision-die sets to achieve the target tube dimensions with tight tolerances (±0.05 mm). Cold working enhances the mechanical properties through strain hardening while maintaining the austenitic microstructure.
  4. Intermediate Annealing: Periodic solution annealing (at 1050°C – 1150°C in controlled atmosphere) is performed during the drawing process to relieve accumulated residual stresses and restore ductility, preventing cracking or deformation during subsequent forming operations.
  5. Spiral Coiling / Winding: The formed tubes are precisely coiled using CNC-controlled winding machines to achieve the specified coil diameter and pitch. The winding process is optimized to minimize kinking, ovality, and mechanical stress concentrations.
  6. Fin Attachment (if applicable):strong> Aluminum fins are mechanically bonded or welded onto the coiled tubes using high-frequency welding or mechanical pressing techniques. Fin-to-tube bonding strength is verified per AHRI 210/240 standards.
  7. End Forming and Brazing: Tube ends are prepared for connection to headers or manifolds. Brazing joints (if applicable) are performed under argon shielding to prevent oxidation, and joint integrity is verified by helium leak testing (per ASTM F2329).
  8. Final Hydrostatic Pressure Testing: Each coil tube assembly is subjected to a hydrostatic pressure test at 1.5× the maximum working pressure for a minimum dwell time of 30 seconds. Zero leakage is the acceptance criterion.
  9. Final Inspection and Packaging: Dimensional verification (OD, WT, coil diameter), surface finish inspection, and visual examination are conducted. Products are packaged with anti-corrosion wrapping and moisture-absorbent desiccants for safe transport.

Applications

The stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. are specifically engineered for the following applications:

  • Fan Coil Units (FCUs): Primary application — serving as the evaporator or condenser coil in ceiling-mounted, concealed, or wall-mounted fan coil units used in commercial buildings, hotels, hospitals, and residential HVAC systems.
  • Air Handling Units (AHUs): Used as heat exchange elements in rooftop and ducted air handling systems for large-scale commercial and industrial facilities.
  • Chilled Water Systems: Ideal for closed-loop chilled water systems where corrosion resistance is paramount, particularly in applications involving treated water or condensate with variable pH levels.
  • Refrigeration and Heat Pump Systems: Suitable for medium-pressure refrigerant circuits in heat pump water heaters and industrial refrigeration units requiring stainless steel construction.
  • Marine and Coastal HVAC Systems: The 316L grade coil tubes provide exceptional resistance to chloride-induced pitting corrosion, making them ideal for marine vessels, coastal buildings, and humid tropical environments.
  • Food Processing and Pharmaceutical HVAC: The hygienic surface finish and corrosion-resistant properties meet the stringent requirements of food-grade and pharmaceutical-grade ventilation systems.

Addressing Typical Fan Coil Unit Problems

Based on the technical insights derived from the study "Analysis of Typical Problems in Fan Coil Unit Usage," Wenzhou Jixing's coil tube products are specifically designed to mitigate the following common field issues:

  • Thermal Efficiency Degradation: Scale buildup and fouling reduce heat transfer efficiency over time. The smooth, polished surface finish (Ra ≤ 0.4 μm) of these coil tubes minimizes fouling factor accumulation, maintaining high heat transfer coefficients throughout the service life.
  • Corrosion and Leaks: Inferior materials lead to intergranular corrosion and eventual failure. The austenitic stainless steel construction provides inherent resistance to both general and localized corrosion, significantly extending service life beyond carbon steel alternatives.
  • Mechanical Vibration Damage: Continuous operation of fan motors induces vibration that can fatigue and crack inferior coil tubes. The high tensile strength (≥ 515 MPa) and excellent fatigue resistance of 304/316L stainless steel ensure structural integrity under prolonged vibrational loading.
  • Water Hammer and Pressure Transients: The robust wall thickness options and high pressure rating (up to 1.6 MPa) provide adequate safety margins against transient pressure spikes common in hydronic HVAC systems.

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework and holds the following certifications to ensure product reliability and regulatory compliance:

Certification / Standard Scope Validity
ISO 9001:2015 Quality Management System — Full manufacturing process Current
ISO 14001:2015 Environmental Management System Current
CE Marking (EU) Compliance with European Pressure Equipment Directive (PED 2014/68/EU) Current
EN 10204 Type 3.1 Mill Test Certificates for material traceability Per batch
ASTM A213 / A269 Material and product specification compliance Per batch
GB/T 12771 Chinese National Standard for welded stainless steel tubes Per batch
ASME BPV Code (if applicable) Boiler and Pressure Vessel Code compliance for high-pressure applications On request

Unique Selling Points

  • Application-Specific Design: Unlike generic coil tubes, these products are engineered specifically to address the thermal, mechanical, and corrosion challenges unique to fan coil unit operation, informed by field-failure analysis and academic research.
  • Dual-Grade Material Options: Customers can select between 304 (cost-effective, general-purpose) and 316L (premium, chloride-resistant) grades to match their specific environmental and economic requirements.
  • Precision Dimensional Control: Tolerance of ±0.05 mm on wall thickness and ±0.02 mm on outer diameter ensures seamless integration into heat exchanger assemblies and minimizes air bypass losses.
  • Extended Service Life: Superior corrosion resistance and mechanical durability deliver a design life exceeding 20 years under normal operating conditions, significantly reducing lifecycle replacement costs.
  • Customization Capability: Full customization of OD, wall thickness, coil diameter, tube length, and fin configuration to meet OEM-specific design requirements.
  • Comprehensive Quality Traceability: Every coil tube batch is accompanied by a full set of documentation including MTC, pressure test reports, and dimensional inspection records, ensuring complete supply chain traceability.

Technical Notes and Recommendations

For optimal performance in fan coil unit applications, the following engineering considerations are recommended:

  • Water Treatment: Even with stainless steel construction, proper water treatment (pH 6.5–8.5, conductivity < 500 μS/cm) is essential to prevent galvanic corrosion at dissimilar metal joints and to minimize scale formation.
  • Flow Velocity: Maintain water flow velocity between 0.5 m/s and 1.5 m/s to balance heat transfer efficiency against erosion-corrosion risk.
  • Installation Orientation: Ensure proper drain slope (minimum 1:100) to prevent water stagnation and condensation-related corrosion.
  • Periodic Inspection: Recommend annual visual inspection of coil tube surfaces and semi-annual pressure testing for systems operating above 1.0 MPa.

Contact Information

For detailed product inquiries, custom specifications, or technical consultation regarding fan coil unit coil tube applications, please contact:

Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Catalog Reference: No. 8