Stainless Steel Coil Tube (Coiltube) — Technical Specification
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, continuously coiled tubular product designed for high-performance applications in HVAC (Heating, Ventilation, and Air Conditioning), fluid transport, and industrial heat exchange systems. This product is specifically engineered to meet the stringent requirements of fan coil unit (FCU) assemblies, where thermal efficiency, flow resistance characteristics, and long-term corrosion resistance are critical performance parameters.
Unlike discrete straight tubes, the coil tube is produced as a continuous, spring-coiled configuration that allows for maximum heat transfer surface area within a compact volumetric envelope. This geometry is the foundational component of modern fan coil units, air handling units, and compact heat exchangers used across commercial, industrial, and residential building services sectors.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades conforming to international metallurgical standards. The primary grades utilized include:
- ASTM A213 TP304 / TP304L — General-purpose austenitic grade offering excellent weldability, formability, and corrosion resistance in non-reducing environments.
- ASTM A213 TP316 / TP316L — Molybdenum-enhanced grade providing superior resistance to pitting and crevice corrosion, suitable for chlorinated or aggressive fluid environments.
- ASTM A213 TP316L — Low-carbon variant of TP316, designed to minimize intergranular corrosion during welding operations.
Key Metallurgical Properties
- Chemical Composition: Carbon (C) ≤ 0.08% (L-grades ≤ 0.03%), Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5%, Molybdenum (Mo) 2–3% (for 316 grades)
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild chemical environments; pitting resistance equivalent number (PREN) ≥ 19 for 316L grade
- Temperature Range: Serviceable from cryogenic temperatures (−196°C) up to 870°C (oxidation limits)
- Mechanical Properties: Minimum tensile strength 515 MPa (annealed condition); elongation ≥ 35%
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 100°C, ensuring efficient thermal transfer
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.0 mm (customizable) |
| Wall Thickness | 0.35 mm – 1.20 mm |
| Coil Pitch | 12 mm – 40 mm (adjustable per application) |
| Coil Diameter | 100 mm – 500 mm (standard delivery) |
| Tube Length per Coil | Continuous; standard cut lengths 1.5 m – 6.0 m |
| Surface Finish | 2B Annealed / BA (Bright Annealed) / Custom polished |
| Internal Surface Roughness (Ra) | ≤ 0.8 μm (BA finish); ≤ 1.6 μm (2B finish) |
| Dimensional Tolerance (OD) | ±0.05 mm |
| Dimensional Tolerance (Wall) | ±10% of nominal |
| Coil Pitch Tolerance | ±0.5 mm |
| Material Grade | 304, 304L, 316, 316L (ASTM A213) |
| Standard Conformity | ASTM A213, GB/T 17863, EN 10216-5 |
| Maximum Working Pressure | Up to 1.6 MPa (design dependent) |
| Maximum Working Temperature | 120°C (typical HVAC service); up to 350°C (industrial) |
| Delivery Form | Continuous coil / Cut-to-length coiled sections |
Manufacturing Process
The production of precision stainless steel coil tubes involves a multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Hot-Rolled Seamless Tube Production: Raw stainless steel billets are hot-rolled and pierced to produce seamless tubes. The hot-rolling process establishes the initial geometry and achieves full recrystallization of the austenitic microstructure.
- Cold Drawing / Cold Rolling (Pilot Drawing): The hot-rolled tube is cold-drawn through precision dies to achieve the required outer diameter and wall thickness with tight tolerances. This cold working step induces beneficial strain hardening while maintaining the solution-annealed austenitic structure.
- Solution Annealing: The cold-worked tube is solution-annealed at 1050–1100°C followed by rapid water quenching. This process dissolves carbides, eliminates residual stresses, and restores full ductility and corrosion resistance.
- Pickling and Passivation: The annealed tube undergoes acid pickling (typically hydrofluoric/nitric acid mixture) to remove oxide scale, followed by passivation to establish a stable, protective chromium oxide film (Cr₂O₃) on the surface.
- Coiling / Coil Forming: The straight, annealed tube is fed through a precision coiling head with calibrated die sets to form the helical coil geometry. The coiling process is performed at controlled speeds to prevent tube flattening, ovality, or micro-cracking at the coil bends.
- Dimensional Inspection and Quality Control: Each coil is inspected for outer diameter, wall thickness, coil pitch uniformity, and surface defects using automated optical measurement systems and ultrasonic thickness gauges.
- Packaging and Marking: Finished coils are wrapped in protective plastic film, placed on wooden pallets or steel crating, and marked with mill certificates, heat numbers, and dimensional identification.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. serves as a critical component across multiple high-value industrial and commercial sectors:
- Fan Coil Units (FCUs): The primary application. The coil tube forms the heat exchange core of fan coil units used in commercial buildings, hotels, hospitals, and data centers for precise temperature and humidity control. The coil geometry maximizes the surface-to-volume ratio, enabling efficient heat transfer between the refrigerant or hot water circuit and the airstream.
- Air Handling Units (AHUs): Used in large-scale HVAC systems where coil tubes are integrated into larger heat exchanger assemblies for heating, cooling, and latent load management.
- Industrial Process Heat Exchangers: Spiral-wound and coil-type heat exchangers in chemical processing, pharmaceutical manufacturing, and food-grade applications where sanitary-grade materials are required.
- Automotive and Marine HVAC: Compact coil tube assemblies for climate control in vehicles, marine vessels, and rail transit systems.
- Refrigeration and Cryogenic Systems: Stainless steel coil tubes withstand cryogenic temperatures without embrittlement, making them suitable for ammonia, CO₂, and mixed-refrigerant systems.
- Sanitary and Food Processing: 316L-grade coil tubes are employed in dairy processing, beverage manufacturing, and pharmaceutical equipment where CIP (Clean-in-Place) and SIP (Sterilize-in-Place) protocols are required.
- Geothermal and Solar Thermal Systems: Coil tubes used as heat collection elements in ground-source heat pumps and solar thermal collectors.
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications and complies with the following standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and customer satisfaction.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 3.1 Material Test Certificates — Each shipment is accompanied by third-party witnessed material test certificates verifying chemical composition, mechanical properties, and dimensional conformity.
- Mill Test Reports (MTRs) — Full traceability documentation including heat numbers, chemical analysis, tensile test results, and hardness data.
- Compliance Standards: ASTM A213, ASTM A269, GB/T 17863, EN 10216-5, JIS G3459
- Third-Party Inspection: Available upon request through SGS, Bureau Veritas, or TÜV Rheinland.
Unique Selling Points
- Precision Coil Geometry: Consistent coil pitch tolerance of ±0.5 mm ensures uniform flow distribution and predictable pressure drop across the heat exchanger, directly contributing to the comprehensive performance indicators of fan coil units — including cooling capacity, heating efficiency, and airflow resistance.
- Superior Surface Quality: BA (Bright Annealed) finish achieves internal surface roughness of Ra ≤ 0.8 μm, minimizing fouling accumulation and maintaining long-term thermal performance with reduced cleaning frequency.
- Full Traceability: Every coil is linked to its mill heat number with complete metallurgical documentation, enabling lifecycle performance tracking and failure analysis.
- Multi-Grade Availability: Seamless supply of 304, 304L, 316, and 316L grades from a single source, simplifying supply chain management for OEMs with diverse product portfolios.
- Customization Capability: Flexible customization of outer diameter, wall thickness, coil pitch, and coil diameter to meet specific OEM design requirements without minimum order quantity constraints.
- Enhanced Corrosion Resistance: Solution-annealed and passivated surface provides a stable chromium oxide passive film, ensuring service life exceeding 25 years in typical HVAC applications with minimal degradation of heat transfer performance.
Note: The comprehensive performance evaluation of fan coil units — encompassing thermal capacity, airflow characteristics, pressure drop, and energy efficiency — is directly dependent on the geometric precision, material quality, and surface finish of the coil tube core. Wenzhou Jixing Metal Materials Co., Ltd. delivers coil tubes engineered to optimize every dimension of this evaluation framework.