Stainless Steel Coil Tube (Coiltube) — HVAC & Industrial Applications
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for use in Fan Coil Units (FCUs), Heat Exchangers, and various Heating, Ventilation, and Air Conditioning (HVAC) systems. The coil tube is supplied in continuous coiled form, enabling efficient downstream processing such as bending, forming, and fabrication into compact heat exchange coils. The product integrates superior corrosion resistance, thermal conductivity, and mechanical durability, making it an ideal choice for both residential and commercial HVAC installations as well as industrial process applications.
The design philosophy behind this coil tube product is closely aligned with the requirements of automated temperature control systems, including those utilizing Microcontroller Unit (MCU)-based thermostats such as those based on the TI MSP430 architecture. The coil tube's consistent geometry and material homogeneity ensure reliable thermal performance in closed-loop temperature regulation systems, where precise heat transfer is critical for maintaining setpoint accuracy within ±0.5°C.
2. Material & Properties
2.1 Base Material
The coil tube is manufactured from high-grade Stainless Steel, primarily using the following grades:
- AISI 304 (UNS S30408) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- AISI 316 (UNS S31608) — Enhanced molybdenum-bearing grade offering superior resistance to pitting and crevice corrosion in aggressive environments.
- AISI 321 (UNS S32108) — Stabilized grade with titanium addition for improved high-temperature oxidation resistance.
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (for 304 grade)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (HB): ≤ 210 (annealed condition)
- Density: 7.93 g/cm³
2.3 Thermal Properties
- Thermal Conductivity (at 20°C): 16.3 W/(m·K) (304 grade)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /K
- Specific Heat Capacity: 500 J/(kg·K)
- Maximum Service Temperature: 870°C (continuous), 1150°C (intermittent)
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, dilute acids, and alkaline solutions
- 316 grade: Superior resistance to chlorides, seawater, and industrial chemicals
- Passive chromium oxide film (Cr₂O₃) provides self-healing protective layer
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (customizable) | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.5 mm – 1.5 mm | ASTM A213 / GB/T 14976 |
| Coil Length (per roll) | 50 m – 500 m (standard); up to 1000 m (special order) | — |
| Coil Inner Diameter | 150 mm – 300 mm | — |
| Surface Finish | Bright Annealed (BA), Pickled & Passivated, or Custom Polished | ASTM A478 |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade); ±0.1 mm (standard) | GB/T 14976 |
| Dimensional Tolerance (Wall) | ±10% of nominal | GB/T 14976 |
| Weld Seam | Double-side welded with internal & external grinding; or seamless | ASTM A213 |
| Maximum Working Pressure | Up to 1.6 MPa (standard); 4.0 MPa (thick-wall variant) | GB/T 12459 |
| Operating Temperature Range | −196°C to +600°C | — |
| Material Grade Options | 304, 304L, 316, 316L, 321, 310S | ASTM A213 |
| Packaging | Wooden reel / steel drum with moisture-proof wrapping | — |
| Minimum Order Quantity (MOQ) | 500 kg per grade | — |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, material integrity, and surface quality:
4.1 Process Flow
- Raw Material Selection: High-purity stainless steel wire rod sourced from certified mills, subjected to incoming spectral analysis (OES) for chemical composition verification.
- Wire Drawing: Multi-stage cold drawing through tungsten carbide (WC) dies to achieve precise wire diameter and mechanical properties.
- Coil Forming / Pipe Forming: Formed wire is fed through a die set to create the tubular geometry. For welded tubes, a high-frequency induction welding (HFI) process joins the edges with precision control of weld parameters.
- Weld Seam Grinding: Both internal and external weld seams are ground to minimize residual stress and ensure uniform wall thickness.
- Intermediate Annealing: Controlled heating in a protective atmosphere (argon or dissociated ammonia) to relieve residual stresses and restore ductility.
- Final Coiling: The tube is wound onto precision reels at controlled tension to prevent deformation, kinking, or springback.
- Surface Treatment: Acid pickling and passivation treatment to remove scale and establish a stable chromium oxide passive layer.
- Quality Inspection: Hydrostatic pressure testing, dimensional measurement, visual inspection, and non-destructive testing (NDT) including eddy current and ultrasonic examination.
- Packaging & Dispatch: Protective wrapping, moisture barrier application, and secure mounting on shipping reels or drums.
4.2 Key Process Controls
- Welding Parameter Control: Induction welding frequency (50 kHz–100 kHz), welding speed, and electrode alignment are monitored in real time by PLC systems.
- Annealing Atmosphere: Dew point maintained below −60°C to prevent oxidation during heat treatment.
- Coiling Tension: Precisely controlled at 30–80 N/m² to prevent surface scratches or deformation.
- In-Process Inspection: Automated laser measurement systems verify OD and wall thickness at intervals of every 10 meters.
5. Applications
5.1 HVAC & Fan Coil Units
The primary application domain for this coil tube product is in the fabrication of heat exchange coils for Fan Coil Units (FCUs). The coil tube is bent into serpentine or zigzag patterns and combined with aluminum fins to create efficient air-to-water heat exchangers. The consistent thermal properties and smooth internal bore minimize flow resistance and maximize heat transfer coefficients, ensuring optimal performance in temperature regulation systems.
5.2 Industrial Heat Exchangers
- Shell-and-tube heat exchangers for chemical processing
- Condensers and evaporators in refrigeration systems
- Plate-fin heat exchangers for cryogenic applications
- Air preheaters and economizers in boiler systems
5.3 Fluid Conveyance Systems
- Food and beverage processing pipelines (FDA-compliant 304/316 grades)
- Pharmaceutical fluid transfer systems
- Chemical processing and transport lines
- Marine and offshore fluid handling
5.4 Temperature Control Systems
In automated temperature control applications — such as those governed by Microcontroller Unit (MCU)-based thermostats (e.g., systems utilizing the TI MSP430 low-power microcontroller platform) — the coil tube serves as the primary heat exchange element. The thermostat controller monitors ambient temperature via sensors and modulates refrigerant or hot water flow through the coil tube to maintain precise temperature setpoints. The coil tube's uniform thermal conductivity and predictable heat transfer characteristics are essential for achieving stable closed-loop control with minimal overshoot and fast response times.
5.5 Additional Applications
- Automotive radiator and heater core components
- Medical equipment fluid circuits
- Solar thermal collector absorber tubes
- Geothermal heat pump ground loops
- Electronics cooling and heat dissipation assemblies
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications to ensure full compliance with international and domestic standards:
6.1 Management System Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
6.2 Product & Material Certifications
- EN 10204 3.1 — Manufacturer's Test Certificate (MTC)
- EN 10204 3.2 — Inspection Certificate (third-party verified)
- CE Marking — Conformity with European Directive 2014/68/EU (Pressure Equipment Directive)
- PED (Pressure Equipment Directive) Compliance for pressure-rated applications
- NSF/ANSI 61 — Compliance for potable water contact applications (304/316 grades)
- 3-A Sanitary Standards — For food-grade processing applications
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes
- GB/T 12771 — Chinese national standard for welded stainless steel tubes
6.3 Testing & Inspection Protocols
| Test Type | Method / Standard | Frequency |
|---|---|---|
| Chemical Composition Analysis | OES Spectrometry (ASTM E415) | Per heat/ladle |
| Hydrostatic Pressure Test | ASTM A213 / GB/T 241 | 100% of production |
| Dimensional Inspection | Laser gauge / Micrometer (ASTM A213) | Every 10 m |
| Eddy Current Examination | ASTM E309 | 100% of production |
| Visual Surface Inspection | ASTM A478 | 100% of production |
| Mechanical Testing (Tensile & Hardness) | ASTM A213 / GB/T 228 | Per batch |
| Intergranular Corrosion Test | ASTM A923 Method A (acid solution) | Per grade qualification |
| Pickling & Passivation Verification | Blue dye test / Rust prevention test | Per batch |
7. Unique Selling Points
- Precision Dimensional Control: Tight tolerances (±0.05 mm OD) ensure seamless