Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous tube product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed for applications requiring high static pressure airflow management, particularly in fan coil tube (Fan Coil Unit, FCU) systems integrated with fresh air delivery networks. The coil tube configuration allows for efficient heat exchange surface area maximization within compact spatial footprints, making it an ideal replacement for conventional hot air curtain systems in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) installations.
The product adheres to stringent metallurgical standards and is engineered to withstand prolonged exposure to high-pressure differential environments, corrosion-prone atmospheres, and thermal cycling conditions. The continuous coil form factor eliminates the need for on-site welding or brazing, significantly reducing installation complexity and potential leak points.
2. Material Composition & Properties
2.1 Base Material
- Austenitic Stainless Steel conforming to ASTM A213 / GB/T 14976 specifications
- Primary grades: 304 (UNS S30408), 316L (UNS S31603), and 321 (UNS S32108)
- Minimum tensile strength (Ultimate Tensile Strength, UTS): ≥ 515 MPa (for 304 grade)
- Yield strength (0.2% offset): ≥ 205 MPa
- Elongation at break: ≥ 40% (in the as-supplied condition)
2.2 Key Metallurgical Properties
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, chlorides, and acidic condensate formed in HVAC environments. The 316L grade offers superior resistance to pitting and crevice corrosion due to molybdenum (Mo) content of 2.0–3.0%.
- Cryogenic Performance: Maintains ductility and mechanical integrity at temperatures as low as −196°C, suitable for refrigeration coil applications.
- Thermal Stability: Sustained service temperature range of −40°C to +450°C with minimal grain growth or sensitization.
- Hygienic Surface: Passivated surface finish with a surface roughness (Ra) of ≤ 0.8 μm, preventing biofilm accumulation in wet-coil environments.
2.3 Chemical Composition (Typical — Grade 304)
| Element | Carbon (C) | Chromium (Cr) | Nickel (Ni) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Iron (Fe) |
|---|---|---|---|---|---|---|---|
| Specification | ≤ 0.08% | 18.0–20.0% | 8.0–11.0% | ≤ 2.0% | ≤ 0.045% | ≤ 0.030% | Balance |
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 – 32.0 mm (custom sizes available) | GB/T 14976 / ASTM A213 |
| Wall Thickness (WT) | 0.5 – 2.0 mm | — |
| Coil Pitch | 10 – 25 mm (adjustable per design requirement) | — |
| Coil Diameter | 50 – 500 mm (spiral coil) | — |
| Tube Length (Uncoiled) | 5 – 60 m per continuous coil | — |
| Surface Finish | 2B (mill finish), BA (Bright Annealed), or Electropolished | ASTM A240 |
| Pressure Rating | Up to 1.6 MPa (working pressure, at 20°C) | ASME B31.3 |
| Static Pressure Capability | Up to 500 Pa (for high static pressure FCU integration) | ASHRAE 62.1 |
| Tolerance — OD | ± 0.05 mm | GB/T 14976 |
| Tolerance — Wall Thickness | ± 10% of nominal | — |
| Heat Treatment | Solution annealed at 1010–1150°C, water quenched | ASTM A213 |
| Packaging | Coiled on wooden spools with moisture-barrier wrapping | — |
4. Manufacturing Process
- Strip Selection & Inspection: Cold-rolled stainless steel strip is procured from certified mills and subjected to spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance.
- Slitting & Leveling: The strip is slit to precise width and leveled to eliminate residual stresses that could affect coil geometry consistency.
- Forming (Coil Bending): A precision CNC (Computer Numerical Control) coil-forming machine bends the flat strip into a continuous helical coil at controlled pitch and diameter, with synchronized feed and bending axes to prevent ovality or springback.
- Welding (for welded coil tube): Where a tubular cross-section is required, the formed strip undergoes high-frequency induction welding (HFW) or TIG (Tungsten Inert Gas) welding with argon (Ar) internal shielding to maintain metallurgical integrity at the weld seam.
- Solution Annealing: The welded coil tube is solution-annealed at 1010–1150°C followed by rapid water quenching to dissolve carbide precipitates and restore full austenitic corrosion resistance.
- Pickling & Passivation: The tube is pickled in a mixed acid bath (HNO₃ + H₂SO₄) to remove scale, followed by nitric acid passivation to establish a protective chromium oxide layer (Cr₂O₃).
- Dimensional & NDT Inspection: Each coil is inspected for dimensional accuracy (OD, wall thickness, pitch) and subjected to Non-Destructive Testing (NDT) including dye penetrant testing (PT) on weld seams and eddy current testing for internal defects.
- Pressure Testing: Hydrostatic pressure testing at 1.5× the rated working pressure for a minimum hold time of 30 seconds per coil to verify structural integrity.
- Final Packaging: Coils are wound onto wooden spools, wrapped in polyethylene (PE) film, and labeled with heat number, grade, dimensions, and certification documentation.
5. Applications
5.1 Primary Application — High Static Pressure Fan Coil Systems
The stainless steel coil tube is the core heat exchange element in high static pressure Fan Coil Units (FCUs) that replace conventional hot air curtains. In this configuration, the coil tube is integrated into a ducted system that delivers conditioned fresh air at elevated static pressure (up to 500 Pa), enabling effective air curtain formation at building entrances without the energy waste associated with direct electric resistance heating.
Key Performance Advantage: The coil tube's high surface-area-to-volume ratio, combined with the corrosion-resistant austenitic stainless steel substrate, enables superior heat transfer efficiency (U-value up to 85 W/m²·K) while maintaining structural integrity over extended service life cycles in humid, corrosive environments.
5.2 Additional Applications
- Commercial HVAC: Air handling units (AHUs), rooftop units (RTUs), and VAV (Variable Air Volume) terminal boxes
- Food & Beverage Processing: Sanitary heat exchangers, CIP (Clean-In-Place) systems, and hygienic piping coils
- Pharmaceutical Industry: GMP (Good Manufacturing Practice) compliant process coils for fluid heating and cooling
- Marine & Offshore: Seawater-cooled heat exchangers where chloride resistance is critical
- Automotive & Aerospace: Compact thermal management coils for cabin conditioning and fluid circuits
- Chemical Processing: Corrosive fluid handling coils in acid and alkali processing environments
6. Quality Certifications & Compliance
| Certification / Standard | Scope | Status |
|---|---|---|
| ISO 9001:2015 | Quality Management System (QMS) | Certified |
| ISO 14001:2015 | Environmental Management System (EMS) | Certified |
| CE Marking (EU) | Product conformity with European directives | Available |
| ASTM A213 | Material specification for seamless and welded austenitic stainless steel tube | Compliant |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes | Compliant |
| EN 10216-5 | European standard for welded austenitic stainless steel tubes | Compliant |
| ASME B31.3 | Piping code for process piping pressure design | Design-verified |
| Mill Test Certificate (MTC) | Third-party material certification per EN 10204 Type 3.1 | Provided per batch |
7. Unique Selling Points (USPs)
- Energy Efficiency: The high static pressure coil tube system delivers up to 40% energy savings compared to conventional electric hot air curtains by leveraging the building's existing HVAC infrastructure for air curtain formation.
- Zero-Weld Installation: The continuous coil form factor enables plug-and-play installation without field welding, reducing installation time by up to 60% and eliminating on-site quality variability.
- Extended Service Life: Austenitic stainless steel construction provides a design service life of ≥ 25 years without corrosion-related degradation, even in aggressive atmospheric environments.
- Hygienic & Food-Safe: Passivated surface finish meets FDA 21 CFR and EU 1935/2004 food contact material requirements.
- Custom Engineering: Wenzhou Jixing Metal Materials Co., Ltd offers fully customizable coil geometry, material grade, and dimensional specifications to match specific system design parameters.
- Full Traceability: Each coil is traceable to the original mill heat number with complete chemical and mechanical test data provided per EN 10204 Type 3.1.
8. Technical Reference
Reference Document: 《高静压风机盘管加新风系统取代热空气幕的应用》 — "Application of High Static Pressure Fan Coil Tube with Fresh Air System as a Replacement for Hot Air Curtains." This technical paper documents the thermodynamic analysis, airflow performance modeling, and field validation of the coil tube-based air curtain system, confirming its superiority over resistive heating air curtain alternatives in terms of energy consumption, maintenance frequency, and indoor air quality (IAQ) performance.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd — Specialized in precision stainless steel tube and coil products for industrial and HVAC applications.