Stainless Steel Coil Tube (Fan Coil Unit Heat Exchanger Tube)
Product Code: No. 987 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered heat exchange tube component designed primarily for integration into Fan Coil Units (FCUs) within Heating, Ventilation, and Air Conditioning (HVAC) systems. As a critical functional element in the coil assembly, the tube facilitates thermal transfer between the circulating fluid (chilled water or hot water) and the ambient air stream, enabling efficient temperature modulation in commercial and industrial environments.
Wenzhou Jixing Metal Materials Co., Ltd. has conducted systematic improvement analyses on fan coil unit configurations, optimizing coil tube geometry, material selection, and manufacturing tolerances to enhance thermal efficiency, reduce pressure drop, and extend service life. This product represents the culmination of iterative engineering refinement informed by field performance data and failure mode analysis.
2. Material & Properties
2.1 Material Composition
The coil tube is fabricated from austenitic stainless steel conforming to ASTM A269 (Standard Specification for Seamless Austenitic Stainless Steel Tube for Heat Exchangers and Similar Applications) or equivalent GB/T 12771 (Chinese National Standard for Stainless Steel Seamless Tubes). The primary grade utilized is SUS304 (UNS S30400), with the option of SUS316L (UNS S31603) for corrosive environments.
2.2 Mechanical Properties
| Property | SUS304 Grade | SUS316L Grade | Test Method |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 | ASTM A370 |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | ≥ 170 | ASTM A370 |
| Elongation (% at Break) | ≥ 40 | ≥ 40 | ASTM A370 |
| Impact Energy (J @ -40°C) | ≥ 47 | ≥ 47 | ASTM A370 |
| Density (g/cm³) | 7.93 | 7.98 | — |
| Thermal Conductivity (W/m·K @ 20°C) | 16.3 | 14.6 | ASTM E1461 |
| Linear Expansion Coefficient (×10⁻⁶/K, 20–100°C) | 17.3 | 16.0 | ASTM E228 |
2.3 Chemical Composition (wt%)
| Element | C | Mn | S | P | Cr | Ni | Mo | N |
|---|---|---|---|---|---|---|---|---|
| SUS304 Max | 0.08 | 2.00 | 0.03 | 0.045 | 18.0–20.0 | 8.0–10.5 | — | 0.10 |
| SUS316L Max | 0.03 | 2.00 | 0.03 | 0.045 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | 0.10 |
2.4 Corrosion Resistance
- Pitting Resistance (PREN): SUS304: PREN ≈ 19–20; SUS316L: PREN ≈ 24–26
- Intergranular Corrosion: Resistant per ASTM A269 Section 7 requirements
- Crevice Corrosion: SUS316L grade offers superior resistance in chloride-containing environments
- Acid Resistance: Resistant to dilute sulfuric and phosphoric acids at ambient temperature
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | Ø9.52 mm (3/8"), Ø12.70 mm (1/2"), Ø15.88 mm (5/8") — customizable |
| Wall Thickness | 0.50 mm – 1.20 mm (tolerance ±0.05 mm) |
| Tube Length (Straight Section) | 300 mm – 1,500 mm per pass |
| Coil Configuration | Spiral (helical) or serpentine (U-bend) winding |
| Coil Diameter | Ø150 mm – Ø600 mm (configurable per unit design) |
| Number of Passes | 1 – 4 passes (determined by thermal load requirement) |
| Surface Finish | Bright annealed (BA) or pickled & passivated; Ra ≤ 0.8 μm |
| Operating Pressure | ≤ 1.6 MPa (design); ≤ 2.4 MPa (hydrostatic test) |
| Operating Temperature Range | -40°C to +150°C (continuous); up to +200°C (intermittent) |
| Welding Method | TIG (Tungsten Inert Gas) welding, helium or argon shielding |
| End Preparation | Plain end or flared connection (per customer specification) |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorously controlled sequence of unit operations, each subject to in-process quality verification:
- Raw Material Procurement: Hot-rolled stainless steel coil sourced from certified mills, verified via mill test certificates (MTC) for chemical composition and mechanical properties.
- Slitting: The master coil is slit to precise width using a high-precision slitting line with edge quality inspection to ensure dimensional accuracy within ±0.1 mm tolerance.
- Forming (Roll Forming): Multi-stand roll forming converts the flat strip into a seamless tube profile. The forming process is controlled to minimize work hardening and maintain material ductility for subsequent bending operations.
- Welding: Longitudinal weld seam is produced via Transverse Resistance Welding (TRW) or Laser Welding, followed by backer rod gas cooling to prevent oxidation on the internal surface.
- Bright Annealing: The formed tube is passed through a continuous bright annealing furnace at 1,050–1,150°C under nitrogen or vacuum atmosphere to relieve residual stresses, restore full annealed microstructure, and achieve a clean, oxide-free surface.
- Pickling and Passivation: Chemical treatment using dilute nitric-hydrofluoric acid mixture removes any residual surface scale, followed by passivation to establish a protective chromium oxide layer (Cr₂O₃).
- Coil Winding: The straightened tube is wound into the specified spiral or serpentine configuration using CNC-controlled winding machines. Bend radius is maintained at ≥ 3× OD to prevent cross-sectional ovality exceeding 5%.
- End Welding and Assembly: Header connections are fabricated and TIG-welded to the coil tube ends with full penetration welds verified by visual and dye penetrant inspection.
- Final Inspection: Hydrostatic pressure testing, dimensional verification, and surface quality assessment prior to packaging.
5. Applications
The stainless steel coil tube is a versatile component deployed across multiple industrial and commercial sectors:
- HVAC Systems: Primary application in Fan Coil Units (FCUs), air handling units (AHUs), and unitary air conditioners for commercial buildings, hospitals, and data centers.
- Food and Beverage Processing: Heat exchangers in pasteurization, refrigeration, and beverage conditioning systems where hygienic standards (FDA/3-A compliant) are mandated.
- Pharmaceutical Manufacturing: Cleanroom air conditioning coils requiring resistance to CIP (Clean-In-Place) chemical cleaning agents.
- Marine and Coastal Environments: HVAC coils in offshore platforms and coastal facilities where chloride-induced corrosion is a critical design consideration (SUS316L grade recommended).
- Industrial Process Cooling: Chilled water coils for machine tool temperature control, electronics cooling, and chemical process heat recovery.
- Refrigeration Systems: Evaporator coils in walk-in coolers, freezers, and cold storage facilities operating at sub-zero temperatures.
6. Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity with international and national standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- CE Marking — Compliance with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU)
- ASTM A269/A269M — Seamless austenitic stainless steel tube for heat exchangers
- GB/T 12771 — Chinese National Standard for stainless steel seamless tubes
- GB/T 17395 — Dimensional tolerances for cold-rolled steel tubes
- ASME B31.5 — Process piping design code compliance (for high-pressure applications)
- NSF/ANSI 61 — Drinking water system components (for potable water applications)
Each production batch is accompanied by a Mill Test Certificate (MTC) documenting chemical analysis, mechanical test results, hydrostatic test data, and dimensional inspection records. Third-party inspection services (SGS, BV, TUV) are available upon customer request.
7. Unique Selling Points
The coil tube product from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself through the following value propositions, validated through systematic engineering analysis and field performance improvement studies:
- Enhanced Thermal Efficiency: Optimized coil geometry derived from computational fluid dynamics (CFD) modeling reduces air-side pressure drop by up to 15% while maintaining or improving heat transfer coefficient (U-value), directly reducing fan energy consumption.
- Superior Corrosion Durability: Full annealed microstructure with low carbon content minimizes sensitization risk; SUS316L option provides Mo-enhanced pitting resistance for aggressive environments.
- Precision Dimensional Control: CNC winding ensures uniform bend radius and consistent tube spacing, eliminating thermal bypass zones and ensuring even heat distribution across the coil face.
- Low Maintenance Lifecycle: Passivated surface finish and seamless construction resist fouling and biofilm formation, extending cleaning intervals and reducing total cost of ownership (TCO).
- Customization Capability: Flexible manufacturing infrastructure enables rapid adaptation of coil diameter, pass count, and tube dimensions to meet specific thermal load requirements (±2% capacity accuracy).
- Environmental Compliance: Lead-free and nickel-compliant material options available; manufacturing process adheres to RoHS and REACH regulatory requirements.
Conclusion: The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. represents a technically advanced heat exchange solution that integrates metallurgical excellence with precision manufacturing. Its application in improved fan coil unit designs—validated through systematic engineering analysis—demonstrates measurable performance gains in thermal efficiency, durability, and operational reliability across demanding industrial and commercial HVAC applications.