Stainless Steel Coil Tube (FCU Dry-Condition Heat Exchanger Coil)

Product Overview

The Stainless Steel Coil Tube (hereinafter referred to as "SS Coil Tube") is a precision-engineered helical tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Specifically designed for integration into Fan Coil Units (FCU) operating under dry-condition (no-condensation) scenarios, this product serves as the core heat exchange element in hydronic air-handling systems. The coil tube is fabricated from high-grade austenitic stainless steel, forming a continuous helical geometry that maximizes surface-area-to-volume ratio, thereby enhancing thermal transfer efficiency while eliminating condensate formation — a critical requirement for hospitality environments such as hotels, where indoor air quality (IAQ) and humidity control are paramount.

This product addresses a well-documented challenge in HVAC engineering: the tendency of conventional copper-fin heat exchangers to produce surface condensation when the coil surface temperature drops below the dew point of ambient air. By employing stainless steel coil tubes with optimized geometry and surface treatment, the SS Coil Tube maintains surface temperatures above the dew point, ensuring condensate-free operation and thereby preventing microbial growth, musty odors, and indoor air quality degradation.

Material & Properties

The SS Coil Tube is manufactured from austenitic stainless steel grades, with the primary material specification as follows:

Key Mechanical and Physical Properties:

Unique Selling Point: The use of austenitic stainless steel — as opposed to the industry-standard copper tube — provides exceptional resistance to corrosion, eliminates copper-bacterial interactions that contribute to Legionella risk, and ensures a service life exceeding 25 years without degradation of heat transfer performance.

Specifications

Parameter Specification Standard / Reference
Product Name Stainless Steel Coil Tube (盘管) —
Material Grade SUS 304 / SUS 316L ASTM A270 / ASTM A269
Outer Diameter (OD) φ6.35 mm (¼"), φ8 mm, φ9.53 mm (⅜") ISO 1127
Wall Thickness 0.5 mm – 1.0 mm ASTM A270 Type 1
Coil Pitch 10 mm – 25 mm (configurable) Custom per FCU design
Coil Diameter 150 mm – 600 mm (configurable) Custom per FCU design
Tube Length (per Coil) 3 m – 15 m (continuous helix) —
Surface Treatment Mirror polish / Electropolishing / Passivation ASTM A967
Pressure Rating ≥ 1.0 MPa (10 bar) working pressure ISO 4414
Heat Transfer Coefficient U-value: 800 – 1,200 W/(m²·K) ASHRAE Handbook
Fin Material (if finned) Aluminum (Al) or Stainless Steel (SS) ASME A106
Operating Fluid Hot water / Chilled water / Glycol-water mixture —
Corrosion Protection Intrinsic (passive Cr₂O₃ layer); optional coating ASTM G15
Compliance Standards GB/T 14976, EN 10216-5, ASME B31.9 —
Service Life ≥ 25 years (in HVAC hydronic service) —

Manufacturing Process

The production of the SS Coil Tube follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, mechanical integrity, and surface quality:

  1. Raw Material Selection & Incoming Inspection:

    Stainless steel seamless or welded tube blanks conforming to ASTM A270/A269 specifications are sourced from certified mill suppliers. Each batch undergoes spectroscopic analysis (OES) for chemical composition verification, hydrostatic pressure testing, and dimensional inspection.

  2. Tube Straightening & Cutting:

    Raw tubes are fed through a rotary straightener to achieve straightness tolerances of ≤ 0.3 mm/m. Precision cutting is performed using cold saws to achieve ±0.5 mm length accuracy.

  3. End Finishing & Threading:

    Tube ends are deburred, chamfered, and threaded (where applicable) to ensure leak-free brazing or welding joints during FCU assembly.

  4. Helical Coiling (Cold Forming):

    Continuous tube is fed into a CNC-controlled coiling machine that winds the tube into the specified helical geometry. The coiling process is performed at room temperature to avoid work-hardening effects that could compromise the tube's fatigue resistance. Parameters including coil pitch, coil diameter, and winding speed are precisely controlled via programmable logic controller (PLC) systems.

  5. Stress Relief Annealing (if required):

    For coils subjected to significant cold-working, a controlled annealing cycle at 850–1,050°C followed by air cooling may be applied to relieve residual stresses and restore full ductility.

  6. Surface Treatment:

    The coil undergoes mechanical polishing (using abrasive belts and wheels) or electrochemical polishing to achieve a mirror surface finish (Ra ≤ 0.4 μm). A final passivation treatment (using nitric acid or citric acid solution per ASTM A967) is applied to enhance the passive chromium oxide layer and maximize corrosion resistance.

  7. Quality Inspection & Testing:

    Each coil unit undergoes:

    • Dimensional verification (OD, wall thickness, coil pitch, coil diameter) using calipers, micrometers, and laser scanners
    • Hydrostatic pressure testing at 1.5× working pressure (≥ 1.5 MPa) for 10 minutes with zero leakage tolerance
    • Visual inspection for surface defects, weld integrity, and finish quality
    • Optional: Eddy current testing (ECT) for subsurface defect detection
  8. Packaging & Dispatch:

    Finished coils are wrapped in protective film, placed in wooden crates or custom pallets, and labeled with batch identification, material certificate, and test report for traceability.

Applications

The SS Coil Tube is purpose-engineered for HVAC hydronic systems where dry-condition operation is required. Primary applications include:

Unique Selling Point: The SS Coil Tube's application in dry-condition fan coil units for hotel projects represents a significant advancement over conventional copper-tube FCUs. By eliminating condensate, it removes the root cause of indoor air quality complaints — one of the most common and costly issues in hospitality HVAC systems — resulting in reduced maintenance frequency, lower energy consumption (no condensate pump), and extended equipment lifespan.

Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and holds the following certifications and complies with the following international and national standards:

All production batches are subject to third-party inspection programs coordinated by recognized testing agencies (e.g., SGS, Bureau Veritas, TÜV Rheinland), ensuring independent verification of material properties, dimensional accuracy, and performance characteristics.

Summary of Unique Selling Points

  1. Condensate-Free Operation: Engineered for dry-condition FCU applications, eliminating the primary source of indoor air quality degradation in hospitality environments.
  2. Superior Corrosion Resistance: Austenitic stainless steel construction provides decades of service life without degradation, even in aggressive environments.
  3. Hygienic Surface Finish: Mirror-polished and passivated surfaces resist bacterial adhesion and facilitate cleaning, meeting the most stringent hygiene standards.
  4. Legionella Risk Mitigation: The absence of copper eliminates the copper-bacterial interaction pathway, reducing Legionella proliferation risk in hydronic systems.
  5. Energy Efficiency: Elimination of condensate pumps and associated drainage infrastructure reduces parasitic energy loads in HVAC systems.
  6. Full Traceability: Every coil is traceable to its raw material batch via EN 10204 Type 3.1 certificates, ensuring supply chain transparency and quality assurance.