Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Product No. 1366) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular product formed into a continuous helical or serpentine coil configuration. Designed primarily for thermal exchange applications, this coil tube serves as a critical component in fan coil units (FCU), heat energy metering systems, and HVAC (Heating, Ventilation, and Air Conditioning) assemblies. The product leverages the inherent advantages of austenitic stainless steel — including exceptional corrosion resistance, high thermal conductivity, and long-term structural integrity — to deliver reliable heat transfer performance under demanding operating conditions.
The coil tube is fabricated from seamless or welded stainless steel pipe, cold-formed into precise coil geometries with controlled pitch, diameter, and wall thickness. This manufacturing approach ensures uniform flow characteristics, minimal turbulence-induced pressure drop, and optimal surface-area-to-volume ratios essential for efficient thermal exchange. The product is particularly suited for integration into fan coil unit temperature control systems and heat energy metering instruments, where precise and stable thermal performance is paramount.
2. Material & Properties
2.1 Material Grades
- 304 (UNS S30400 / 1.4301) — General-purpose austenitic grade offering excellent corrosion resistance, formability, and weldability. Suitable for most HVAC and water-based thermal applications.
- 316 (UNS S31600 / 1.4401) — Enhanced austenitic grade with molybdenum addition, providing superior resistance to chlorides, acids, and aggressive chemical environments. Ideal for marine, industrial, or chemical processing applications.
- 316L (UNS S31603 / 1.4404) — Low-carbon variant of 316, designed for improved resistance to intergranular corrosion during welding operations. Recommended for critical heat exchanger applications requiring post-weld service without sensitization.
- 321 (UNS S32100 / 1.4541) — Titanium-stabilized austenitic grade offering enhanced resistance to high-temperature scaling and stress corrosion cracking. Suitable for elevated-temperature thermal systems.
2.2 Mechanical Properties (Typical — Grade 304, Annealed)
- Tensile Strength: ≥ 520 MPa (≥ 75,400 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (≥ 29,700 psi)
- Elongation: ≥ 40% (in 50 mm / 2 in gauge length)
- Hardness: ≤ 210 HB (Brinell)
- Density: 8.0 g/cm³
2.3 Thermal & Physical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
- Specific Heat: 0.50 J/(g·°C) at 20°C
- Maximum Service Temperature: 870°C (oxidation resistance limit)
- Corrosion Resistance: Excellent against atmospheric corrosion, dilute acids, alkaline solutions, and organic compounds
2.4 Surface Finish Options
- 2B Finish: Cold-rolled, annealed, and pickled; moderate surface roughness (Ra ≤ 0.8 μm); suitable for general industrial applications.
- No. 4 Finish: Fine ground surface with uniform matte appearance (Ra ≤ 0.4 μm); commonly specified for HVAC and visible applications.
- Mirror Finish (8K): Polished to reflective quality (Ra ≤ 0.1 μm); used in high-end architectural and food-grade applications.
- Electropolished: Electrochemically smoothed and passivated (Ra ≤ 0.05 μm); provides enhanced hygienic and corrosion-resistant surface for pharmaceutical and food processing.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 50.8 mm (1/8" – 2") | ASTM A213 / ASME SA-213 |
| Wall Thickness (WT) | 0.4 mm – 3.0 mm (0.016" – 0.118") | ASTM A213 / ASME SA-213 |
| OD Tolerance | ±0.10 mm (±0.004") for OD ≤ 12.7 mm; ±0.13 mm for OD > 12.7 mm | ASTM A213 |
| Wall Thickness Tolerance | ±10% of nominal (minimum ±0.05 mm) | ASTM A213 |
| Coil Pitch (Center-to-Center) | 10 mm – 150 mm (configurable per design) | Custom / Project-Specific |
| Coil Turn Diameter | 25 mm – 500 mm (configurable per design) | Custom / Project-Specific |
| Coil Length (Tube Length) | 1 m – 50 m (continuous or cut-to-length) | Custom / Project-Specific |
| Number of Turns | 2 – 500+ (configurable) | Custom / Project-Specific |
| End Preparation | Plain, beveled, threaded (NPT/BSP), or flanged | ASME B1.20.1 / B1.20.2 |
| Surface Roughness (Internal) | Ra ≤ 0.8 μm (standard); Ra ≤ 0.2 μm (electropolished) | ASTM A213 |
| Maximum Operating Pressure | Up to 4.0 MPa (580 psi) at 20°C (design-dependent) | ASME BPV Code / PED 2014/68/EU |
| Maximum Operating Temperature | −196°C to +450°C (continuous service) | ASTM A213 |
| Coating / Passivation | Pickled and passivated; optional PTFE or ceramic coating available | ASTM A967 / A380 |
| Hydrostatic Test Pressure | 1.5 × design pressure (minimum 3.0 MPa) | ASTM A213 / ASME SA-213 |
| Delivery Condition | Annealed (Solution Annealed), Stress-Relieved | ASTM A213 |
| Packaging | Wooden crate, palletized with moisture barrier; individual coil protection | ISO 11607 / Custom |
4. Manufacturing Process
4.1 Raw Material Procurement
High-purity stainless steel seamless tubes or ERW (Electric Resistance Welded) pipes conforming to ASTM A213/ASME SA-213 or EN 10216-5 are sourced from certified mills. Incoming material undergoes rigorous inspection including chemical composition analysis (via OES — Optical Emission Spectroscopy), mechanical testing (tensile and hardness), and visual surface examination to ensure compliance with specified grades.
4.2 Pre-Forming Preparation
- Cutting: Seamless tubes are cut to required coil-forming lengths using precision plasma or laser cutting systems, with end faces ground flush to minimize stress concentrations.
- End Finishing: Tube ends are deburred, chamfered, and cleaned to remove oxide scale and processing residues. Internal surfaces are inspected via borescope for weld seam integrity (in the case of ERW tubes).
- Heat Treatment: Tubes are solution annealed at 1010–1150°C followed by rapid water quenching to achieve a fully austenitic microstructure with optimal mechanical properties and corrosion resistance.
4.3 Coil Forming
- Cold Bending: Tubes are cold-formed into helical or serpentine coil geometries using CNC-controlled rotary draw bending or mandrel bending machines. The bending process is carefully controlled to prevent wall thinning (limited to ≤ 10% reduction) and ovality (limited to ≤ 3% of nominal OD).
- Springback Compensation: Numerical simulation and empirical data are used to compensate for elastic springback, ensuring the final coil geometry meets dimensional tolerances within ±0.5 mm.
- Multi-Axis Forming: For complex coil configurations (e.g., double-helix or planar serpentine), multi-axis CNC forming machines are employed to achieve precise three-dimensional geometries.
4.4 Post-Forming Treatment
- Stress Relief: Formed coils undergo stress-relief annealing at 400–550°C to eliminate residual bending stresses, ensuring dimensional stability during subsequent welding and service.
- Pickling and Passivation: Coils are immersed in a mixed acid bath (nitric acid + hydrofluoric acid) to remove oxide scale, followed by passivation treatment per ASTM A967 to restore the chromium oxide passive layer and enhance corrosion resistance.
- Surface Finishing: Optional electropolishing or mechanical polishing is performed to achieve specified surface roughness requirements.
4.5 Quality Control & Testing
- Dimensional Inspection: Coordinate Measuring Machine (CMM) scanning verifies coil pitch, turn diameter, and overall geometry against CAD models.
- Hydrostatic Testing: Each coil is pressure-tested at 1.5× design pressure with sustained hold time of minimum 60 seconds to verify leak-tightness and structural integrity.
- Penetrant Testing (PT): Surface-breaking defects are detected using fluorescent or visible-dye penetrant inspection per ASTM E165.
- Eddy Current Testing (ECT): Internal and external wall defects are detected using eddy current probes per ASTM E3092.
- Chemical Verification: Final product undergoes spot-check chemical analysis via XRF (X-Ray Fluorescence) to confirm alloy grade compliance.
5. Applications
5.1 Fan Coil Units (FCU) and HVAC Systems
Stainless steel coil tubes are integral components in fan coil units, serving as the primary heat exchange surface where heated or chilled water transfers thermal energy to circulating air. The coil tube's geometry — with controlled pitch and turn diameter — optimizes the balance between heat transfer efficiency and air-side pressure drop. In temperature control systems, the coil tube's thermal mass and conductivity characteristics directly influence the system's response time and temperature regulation accuracy.
5.2 Heat Energy Metering Instruments
In heat energy metering applications, stainless steel coil tubes function as temperature sensing elements or flow channels within metering assemblies. The material's dimensional stability and corrosion resistance ensure long-term calibration accuracy of thermal energy calculations. The coil tube's uniform wall thickness and controlled internal surface finish contribute to predictable fluid flow profiles, which are critical for accurate volumetric flow measurement and heat load calculation (Q = ṁ × ΔT × Cp).
5.3 Additional Applications
- Industrial Heat Exchangers: Shell-and-tube, plate-and-frame, and air-cooled heat exchangers for chemical, petrochemical, and power generation industries.
- Refrigeration & Cryogenic Systems: Evaporators, condensers, and intermediate coolers operating at temperatures as low as −196°C (liquid nitrogen service).
- Food & Beverage Processing: Pasteurization coils, condensers, and heat recovery systems requiring hygienic-grade construction (FDA-compliant, electropolished).
- Pharmaceutical & Biotechnology: Clean-in-Place (CIP) compatible heat exchange coils for sterile processing environments.
- Marine & Offshore: Condensers and heat exchangers in marine propulsion systems and offshore platform utilities, leveraging 316/316L grade chloride resistance.
- Geothermal Systems: Ground-source heat exchange loops and geothermal well completions requiring long-term corrosion resistance in aggressive subsurface environments.
6. Quality Certifications & Compliance
| Certification / Standard | Description | Scope |
|---|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control throughout manufacturing. | Company-wide |
| ISO 14001:2015 | Environmental Management System certification demonstrating commitment to sustainable manufacturing practices. | Company-wide |
| ISO 45001:2018 | Occupational Health and Safety Management System certification. | Company-wide |
| ASTM A213 / ASME SA-213 | Standard specification for austenitic stainless steel seamless, welded, and heavily cold-worked austenitic stainless steel tubing. | Material & product compliance |
| EN 10216-5 | European standard for welded stainless steel tubes for heat exchangers and heat transfer purposes. | Material & product compliance |
| ASME BPV Code (Section I) | American Society of Mechanical Engineers Boiler and Pressure Vessel Code for pressure-containing applications. | Pressure-rated coil assemblies |
| PED 2014/68/EU | European Pressure Equipment Directive compliance for equipment operating above 0.5 bar gauge pressure. | Pressure-rated coil assemblies |