Stainless Steel Coil Tube — HVAC Fan Coil Unit Application
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for use in Heating, Ventilation, and Air Conditioning (HVAC) systems, particularly in fan coil units (FCU). These coil tubes serve as the core heat exchange medium, facilitating efficient thermal transfer between circulating refrigerants or hot water and ambient air. The product is engineered to withstand prolonged exposure to corrosive environments, high-temperature differentials, and cyclic pressure variations inherent in commercial and residential HVAC installations.
Unlike conventional copper or aluminum coil tubes, stainless steel coil tubes offer superior resistance to pitting corrosion, intergranular corrosion, and stress corrosion cracking (SCC), making them ideal for aggressive service conditions including humid tropical climates, coastal installations, and industrial process applications where chemical compatibility is paramount.
2. Material Composition & Properties
The coil tubes are fabricated from austenitic stainless steel grades conforming to international standards, ensuring optimal balance of formability, weldability, and corrosion resistance.
2.1 Commonly Available Grades
- SUS 304 (ASTM A213 TP304): General-purpose austenitic stainless steel with excellent corrosion resistance in mildly aggressive environments. Minimum 18% Chromium (Cr) and 8% Nickel (Ni).
- SUS 316 (ASTM A213 TP316): Enhanced corrosion resistance due to the addition of 2–3% Molybdenum (Mo), suitable for chloride-rich environments and industrial applications.
- SUS 321 (ASTM A213 TP321): Stabilized grade with Titanium (Ti) addition, resistant to intergranular corrosion at elevated temperatures (up to 870 °C).
- SUS 316L (ASTM A213 TP316L): Low-carbon variant of 316, optimized for welding applications with minimal sensitization risk.
2.2 Key Mechanical & Physical Properties (SUS 304 Reference)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (U.T.S.) | ≥ 520 MPa (75,400 psi) | ASTM A240 |
| Yield Strength (0.2% Proof Stress) | ≥ 205 MPa (29,700 psi) | ASTM A240 |
| Elongation (at Break) | ≥ 40% (in 50 mm gauge length) | ASTM A240 |
| Density | 8.0 g/cm³ | — |
| Thermal Conductivity (at 20 °C) | 16.3 W/(m·K) | ASTM E153 |
| Thermal Expansion Coefficient (20–100 °C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
| Operating Temperature Range | −196 °C to +870 °C | ASME Boiler & Pressure Vessel Code |
| Hardness (Annealed) | ≤ 210 HB (Brinell) | ASTM E10 |
3. Technical Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (O.D.) | 3.0 mm – 25.4 mm (1/8" – 1") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.3 mm – 2.0 mm | ASTM A213 / EN 10216-5 |
| Coil Diameter (Bundle) | 200 mm – 1,200 mm (customizable) | ISO 1155 |
| Tube Length (per pass) | 0.5 m – 6.0 m | — |
| Surface Finish | Mirror Polish (Ra ≤ 0.4 μm), Electro-polished (Ra ≤ 0.2 μm), or Passivated Matte | ASTM A240 / GB/T 14301 |
| Maximum Working Pressure | Up to 2.5 MPa (362.6 psi) — dependent on O.D. and wall thickness | ASME B31.3 |
| Hydrostatic Test Pressure | 1.5× Working Pressure (minimum 6.0 MPa) | ASTM A213 |
| End Condition | Plain End, Beveled End, Flared End, or Threaded (customizable) | ASME B1.20.1 |
| Winding Configuration | Spiral Coil, U-Bend Array, or Serpentine Coil | ISO 1155 |
| Material Certification | EN 10204 Type 3.1 / Mill Test Certificate (MTC) | EN 10204 |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorously controlled multi-stage process to ensure dimensional accuracy, metallurgical integrity, and surface quality.
- Raw Material Procurement & Incoming Inspection: Cold-rolled stainless steel strips or seamless tubes are sourced from certified mills. Each batch undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM A213 or equivalent standards.
- Slitting & Leveling: Stainless steel strip is slit to precise widths and leveled to eliminate residual stresses, ensuring uniform coil winding behavior downstream.
- Forming & Welding (for welded tube): Formed strips are longitudinally welded via Transverse Magnetic Pulse Welding (TMPW) or Tungsten Inert Gas (TIG / GTAW) welding. Weld seams are ground flush to achieve Ra ≤ 0.8 μm.
- Heat Treatment & Annealing: Tubes undergo solution annealing at 1,010–1,150 °C followed by rapid air cooling to achieve a fully austenitic microstructure, relieving residual stresses and restoring maximum ductility.
- Precision Sizing & Calibrating: Cold-calibrated dies reduce outer diameter and wall thickness to final specifications with tolerances of ±0.05 mm (O.D.) and ±10% (wall thickness).
- Coil Winding: Tubes are mechanically wound into the required coil geometry (spiral, serpentine, or U-bend) using CNC-controlled winding equipment to maintain consistent pitch and spacing.
- Surface Treatment: Tubes undergo pickling and passivation (per ASTM A967) using nitric acid or citric acid solutions to remove oxidation scale and form a protective chromium oxide (Cr₂O₃) passive film. Electro-polishing may be applied for critical applications requiring Ra ≤ 0.2 μm.
- Pressure Testing & Non-Destructive Testing (NDT): Each coil undergoes 100% hydrostatic pressure testing. Additionally, Eddy Current Testing (ECT) and ultrasonic testing (UT) are performed to detect subsurface defects, weld discontinuities, and wall thickness variations.
- Final Inspection & Packaging: Dimensional verification, visual inspection, and chemical composition re-verification are performed. Tubes are packaged in moisture-proof wrapping with wooden crates or export-grade containers.
5. Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. are deployed across a wide spectrum of industrial and commercial applications:
- HVAC Fan Coil Units (FCU): Primary application — serving as the heat exchange coil in commercial and residential air conditioning systems. The corrosion resistance of stainless steel extends service life significantly in humid or coastal environments compared to copper alternatives.
- Refrigeration & Cold Storage Systems: Used in evaporator and condenser coils where low-temperature operation (down to −196 °C) and high thermal cycling are required.
- Chemical Processing Industries: Heat exchangers and process coils handling aggressive fluids including acids, chlorides, and caustic solutions.
- Food & Pharmaceutical Processing: Sanitary-grade coils (Ra ≤ 0.4 μm) for pasteurization, CIP (Clean-In-Place) systems, and steam sterilization equipment, compliant with FDA and 3-A Sanitary Standards.
- Automotive Radiators & Intercoolers: Lightweight, high-performance heat exchange tubes with superior fatigue resistance.
- Marine & Offshore Equipment: Desalination plant coils, ballast water heat exchangers, and shipboard HVAC systems exposed to saltwater corrosion.
- Power Generation: Condenser tubes and feedwater heaters in thermal and nuclear power plants.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring traceability and compliance with international standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management System
- EN 10204 Type 3.1 — Third-party inspection and material testing certificates
- ASTM / ASME Compliance — Products manufactured in accordance with ASTM A213, A240, A967, and ASME B31.3 codes
- GB/T Standards (China National Standards): GB/T 14976 (seamless stainless steel tubes), GB/T 14301 (passivation), GB/T 12771 (welded stainless steel tubes)
- CE Marking — Compliance with European Directive requirements for pressure equipment (PED 2014/68/EU)
- Mill Test Certificates (MTC) — Provided for every shipment, including chemical composition, mechanical properties, and NDT results
7. Unique Selling Points
Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional resistance to pitting, crevice corrosion, and chloride-induced SCC — outperforming copper and aluminum coils in aggressive environments by a factor of 5–10×.
Extended Service Life: Designed for 20–30 years of continuous operation without degradation of heat transfer efficiency, significantly reducing lifecycle maintenance costs.
Hygienic & Food-Grade Compliance: Available in electropolished finish (Ra ≤ 0.2 μm) suitable for pharmaceutical and food-grade applications per FDA 21 CFR Part 117 and 3-A Standards.
Customizable Geometry: CNC-controlled winding enables precise customization of coil diameter, pitch, number of passes, and end configurations to meet specific OEM requirements.
Full Traceability: Every coil is batch-traceable from raw material mill certificate through final NDT inspection, ensuring complete quality documentation for regulatory and audit purposes.
Thermal Cycling Durability: Withstands millions of thermal expansion/contraction cycles without fatigue failure, validated through accelerated thermal cycling tests per ASTM E1002.