Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous length of stainless steel tubing wound into a helical or spiral coil configuration, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product category encompasses both cold-drawn seamless coil tubes and welded coil tubes, designed for integration into thermal-fluid systems, particularly Fan Coil Units (FCUs) and similar heat exchange assemblies. The coiled geometry maximizes heat transfer surface area within a compact footprint, making it indispensable in HVAC (Heating, Ventilation, and Air Conditioning) applications, industrial heat exchangers, refrigeration circuits, and process piping systems.
The engineering of coil tubes requires careful consideration of bend radius, wall thickness uniformity, and material workability to ensure that the tube maintains its structural integrity and corrosion resistance throughout the coiling process. The product is supplied in continuous coil form, enabling downstream manufacturers to cut-to-length or further form the tube into custom geometries without the need for additional welding or joining operations.
2. Material & Properties
The Coil Tube is manufactured from high-grade austenitic stainless steel, selected for its superior combination of corrosion resistance, mechanical strength, and thermal conductivity. The following grades are typically available:
- AISI 304 / SUS304 (UNS S30400): The most widely used austenitic grade, offering excellent general corrosion resistance, weldability, and formability. Suitable for food-grade, pharmaceutical, and HVAC applications.
- AISI 316 / SUS316 (UNS S31600): Enhanced corrosion resistance due to 2–3% molybdenum (Mo) content, ideal for marine environments, chemical processing, and high-chloride conditions.
- AISI 316L / SUS316L (UNS S31603): Low-carbon variant of 316, preferred for welding applications to minimize intergranular corrosion (IGC) risk.
- AISI 321 / SUS321 (UNS S32100): Titanium-stabilized grade with improved resistance to intergranular corrosion at elevated temperatures (up to 870°C).
- AISI 304L / SUS304L (UNS S30403): Low-carbon variant of 304, designed for heavy welding and cryogenic service.
2.1 Key Material Properties (AISI 304 Reference)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75 ksi) | ASTM A213 / A269 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29.7 ksi) | ASTM A213 / A269 |
| Elongation (at fracture) | ≥ 40% | ASTM A213 / A269 |
| Thermal Conductivity (25°C) | 16.3 W/(m·K) | ASTM E153 |
| Thermal Conductivity (100°C) | 16.3 W/(m·K) | ASTM E153 |
| Specific Heat Capacity (25°C) | 500 J/(kg·K) | ASTM E153 |
| Linear Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E153 |
| Maximum Service Temperature | 870°C (1600°F) | — |
| Corrosion Resistance | Excellent in oxidizing acids; good in atmospheric and aqueous environments | ASTM G48 |
2.2 Chemical Composition (AISI 304 — Typical)
| Element | Minimum (%) | Maximum (%) |
|---|---|---|
| Carbon (C) | — | 0.08 |
| Chromium (Cr) | 18.0 | 20.0 |
| Nickel (Ni) | 8.0 | 10.5 |
| Manganese (Mn) | — | 2.0 |
| Silicon (Si) | — | 1.0 |
| Phosphorus (P) | — | 0.045 |
| Sulfur (S) | — | 0.03 |
3. Dimensions & Specifications
The Coil Tube is manufactured to meet the dimensional tolerances specified in ASTM A269 (Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and General Applications) and ASTM A213 (Seamless Austenitic Stainless Steel Tubing for High-temperature Service). The following dimensional parameters define the product specification:
| Parameter | Range / Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.18 mm – 158.75 mm (1/8" – 6") | ASTM A269 |
| Wall Thickness (WT) | 0.30 mm – 6.35 mm (0.012" – 0.250") | ASTM A269 |
| OD Tolerance (±) | ± 5% (for OD ≤ 12.7 mm); ± 3% (for OD > 12.7 mm) | ASTM A269 |
| WT Tolerance (±) | ± 10% | ASTM A269 |
| Minimum Bend Radius | 3× OD (cold bend); 5× OD (precision formed coil) | — |
| Coil Length (per coil) | 50 m – 200 m (customizable) | — |
| Coil Diameter (wound) | 200 mm – 600 mm | — |
| Surface Finish | Pickled & Passivated (P&P), Bright Annealed (BA), or Custom | ASTM A473 |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.4 μm (fine finish); ≤ 0.2 μm (mirror/polished) | ASTM B436 |
| End Condition | Plain, Beveled, or Threaded (BSP/NPT) | — |
| Welding Method (if applicable) | Automatic Argon Arc Welding (AAW) / Orbital TIG Welding | ASTM A213 |
4. Manufacturing Process
The production of high-quality Stainless Steel Coil Tube involves a multi-stage process chain, each step controlled to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement: High-purity stainless steel strip or round bar stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (Spectrometer) to verify chemical composition compliance with the designated grade specification.
- Forming / Drawing: For seamless coil tubes, hot-rolled or cold-drawn seamless pipe is used as the base material. For welded coil tubes, precision-cut stainless steel strip is formed into a tubular shape via roll-forming, followed by automatic argon arc welding (AAW) to create a continuous weld seam.
- Cold Drawing / Sizing: The formed tube is drawn through a series of progressively reducing dies (multi-pass cold drawing) to achieve the target outer diameter and wall thickness. This process also imparts work-hardening, improving mechanical properties and dimensional precision.
- Heat Treatment (Annealing): The cold-worked tube is annealed at temperatures between 1050°C and 1150°C, followed by controlled cooling (air cooling or quenching), to relieve residual stresses, restore ductility, and stabilize the austenitic microstructure.
- Pickling & Passivation: The annealed tube is subjected to a pickling bath (typically a mixture of nitric acid and hydrofluoric acid) to remove oxide scale, followed by passivation to form a protective chromium oxide (Cr₂O₃) film on the surface, enhancing corrosion resistance.
- Coiling: The straight tube is fed into a precision coiling machine, where it is wound into a helical coil at a controlled bend radius. The coiling process is monitored to prevent ovality, kinking, or excessive work-hardening at the bend regions. Post-coiling stress relief may be applied if required.
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Quality Inspection: Each coil undergoes rigorous inspection, including:
- Visual inspection for surface defects
- Dimensional verification (OD, WT, coil diameter) using calibrated measuring instruments
- Hydrostatic pressure testing to verify wall integrity
- Magnetic particle inspection (MPI) or eddy current testing (ECT) for subsurface defect detection
- Spectroscopic analysis for chemical composition verification
- Mechanical testing (tensile, hardness) on sample coupons
- Packaging & Shipping: Finished coils are wrapped in protective packaging (VCI (Vapor Corrosion Inhibitor) paper, stretch film, and wooden pallets or crates) to prevent surface damage and corrosion during transit.
5. Applications
The Stainless Steel Coil Tube finds extensive application across multiple industries, driven by its corrosion resistance, thermal performance, and mechanical reliability:
5.1 HVAC & Fan Coil Units (FCUs)
In fan coil unit assemblies, the coil tube serves as the primary heat exchange medium, carrying chilled water or hot water through serpentine coil arrangements. The coil geometry maximizes the heat transfer coefficient between the fluid and the air stream. Key performance considerations include:
- Pressure drop across the coil circuit (ΔP)
- Heat transfer rate (Q) and overall heat transfer coefficient (U-value)
- Number of tube rows and fin-to-tube configuration
- Flow velocity and Reynolds number (Re) within the tube
The efficiency of fan coil units utilizing stainless steel coil tubes is governed by the relationship:
Q = U × A × ΔT_lm
where Q = heat transfer rate (W), U = overall heat transfer coefficient (W/m²·K), A = heat transfer surface area (m²), and ΔT_lm = log-mean temperature difference (K).
5.2 Additional Application Domains
- Refrigeration & Cryogenics: Refrigerant piping coils in evaporators, condensers, and heat exchangers.
- Food & Beverage Processing: Sanitary-grade tubing coils for pasteurization, sterilization, and CIP (Clean-In-Place) systems (AISI 304/316L).
- Pharmaceutical Industry: High-purity fluid transfer coils meeting GMP (Good Manufacturing Practice) standards.
- Chemical Processing: Corrosion-resistant coil tubing for aggressive chemical environments (AISI 316/316L).
- Automotive & Aerospace: Fuel lines, brake lines, and hydraulic circuits requiring high-temperature and high-pressure resistance.
- Medical Devices: Tubing coils for dialysis machines, infusion pumps, and surgical instrument components.
- Marine & Offshore: Heat exchanger coils and piping systems in seawater environments.
- Power Generation: Condenser tubes and boiler coil assemblies.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product traceability and compliance with international standards:
- ISO 9001:2015 — Quality Management Systems (QMS)
- ISO 14001:2015 — Environmental Management Systems (EMS)
- ISO 45001:2018 — Occupational Health &