Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Application Grade
Product Overview
The Stainless Steel Coil Tube (also referred to as Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for integration into Fan Coil Units (FCU) and HVAC (Heating, Ventilation, and Air Conditioning) systems. This product represents an advanced solution derived from engineering improvement analyses of fan coil unit assemblies, addressing critical performance bottlenecks related to thermal efficiency, corrosion resistance, and long-term operational reliability.
Unlike conventional copper or carbon steel coil tubes, this stainless steel variant offers superior resistance to chemical degradation, enhanced mechanical durability, and extended service life under demanding environmental conditions. The product has been developed through iterative design optimization informed by real-world failure analysis and performance benchmarking of existing fan coil unit configurations.
Material & Properties
The coil tube is fabricated from high-grade Austenitic Stainless Steel, selected for its exceptional combination of corrosion resistance, formability, and thermal conductivity suitable for heat exchange applications.
- Material Grade: SUS304 / SUS316L (ASTM A213 TP304 / TP316L)
- Chromium (Cr) Content: 18.0–20.0% (SUS304) / 16.5–18.5% (SUS316L)
- Nickel (Ni) Content: 8.0–10.5% (SUS304) / 10.0–14.0% (SUS316L)
- Molybdenum (Mo) Content: ≤0.08% (SUS304) / 2.0–3.0% (SUS316L)
- Carbon (C) Content: ≤0.08% (SUS304) / ≤0.03% (SUS316L — Low Carbon variant)
- Tensile Strength (Ultimate): ≥520 MPa
- Yield Strength: ≥205 MPa
- Elongation at Break: ≥40%
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and intergranular corrosion
- Operating Temperature Range: −196°C to +870°C
- Surface Finish: Mill finish, polished (Ra ≤ 0.4 μm), or electropolished per application requirement
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.70 mm / 15.88 mm (¼", ⅜", ½", ⅝") | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.50 mm – 2.00 mm (customizable) | ASTM A213 / EN 10217 |
| Coil Inner Diameter (ID) | 150 mm – 600 mm | Manufacturer Specification |
| Coil Length (Uncoiled) | Up to 500 m (continuous coil) | ISO 11612 |
| Bend Radius (Minimum) | ≥ 3× OD | GB/T 12771 |
| Surface Tolerance | ±0.05 mm | ASTM A213 |
| Diameter Tolerance | ±0.08 mm | ASTM A213 |
| End Preparation | Sheared / Beveled / Threaded (optional) | ASME B1.20.1 |
| Heat Treatment | Solution Annealed + Pickled | ASTM A213 |
| Weight (Approximate) | 0.35 – 1.80 kg/m (depending on OD & wall thickness) | — |
| Packaging | Wooden coil crate with moisture barrier wrapping | ISO 4126 |
Manufacturing Process
The production of this stainless steel coil tube follows a rigorously controlled multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: Stainless steel strip or seamless tube blanks are procured from certified mills and subjected to spectroscopic analysis (Spark OES) to verify chemical composition conformity with the specified grade.
- Hot Rolling / Extrusion (Upstream): Billet or ingot material is hot-rolled or extruded into seamless tube stock to establish the initial geometry.
- Cold Drawing / Cold Forming: The tube stock undergoes cold drawing through precision dies to achieve the final outer diameter and wall thickness tolerances. This process enhances mechanical properties through work hardening.
- Solution Annealing: The cold-worked tube is heated to 1010–1150°C in a protective atmosphere (argon or vacuum) to relieve residual stresses, restore ductility, and dissolve carbide precipitates. Rapid water quenching follows to lock the austenitic microstructure.
- Pickling & Descaling: The annealed tube is treated with a mixed acid solution (HNO₃ + HF) to remove oxide scale, ensuring a clean, passive surface ready for further processing.
- Coil Winding: The processed tube is wound onto precision mandrels to form the coil configuration. Tension control systems ensure uniform coil lay without kinking or distortion.
- Dimensional Inspection: Each coil undergoes automated diameter, wall thickness, and straightness verification using ultrasonic thickness gauges and laser measurement systems.
- Non-Destructive Testing (NDT): Hydrostatic pressure testing (to 1.5× working pressure) and eddy current inspection are performed to detect internal voids, cracks, or wall thinning.
- Surface Finishing (Optional): Electropolishing or mechanical polishing is applied to achieve the specified surface roughness for hygienic or aesthetic applications.
- Packaging & Marking: Coils are wrapped in protective film, placed in moisture-proof containers, and crated for shipment. Each unit is marked with heat number, grade, dimensions, and traceability code.
Applications
This stainless steel coil tube is engineered for high-performance thermal exchange and fluid transport applications, with particular emphasis on the following sectors:
- Fan Coil Units (FCU): Primary application — serves as the heat exchanger coil element in commercial and residential HVAC systems, replacing traditional copper tubing with superior corrosion resistance and reduced maintenance frequency. The improvement analysis documented in engineering case studies demonstrates measurable gains in thermal transfer efficiency and system longevity.
- Chilled Water & Hot Water Circulation Systems: Used in secondary loop piping and coil assemblies where water chemistry may be aggressive or variable.
- Refrigeration & Cryogenic Systems: Applicable in low-temperature coil assemblies where material toughness at sub-ambient temperatures is critical.
- Industrial Process Heating & Cooling: Deployed in heat exchangers for chemical processing, food and beverage manufacturing, and pharmaceutical production lines.
- Marine & Coastal Environments: SUS316L grade provides enhanced resistance to chloride-induced pitting in marine HVAC installations.
- Water Treatment & Purification Systems: Used in coil-based heating elements for water treatment plants where hygienic standards are paramount.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality assurance framework ensuring that every coil tube product meets international standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health & Safety Management System
- ASTM A213 / A269 — Specifications for Austenitic Stainless Steel Seamless/Electro-Pneumatic Tubes
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes
- EN 10217-7 — European Standard for Stainless Steel Tubes for Heat Exchangers
- ASME BPV Section I — Compliance for pressure vessel and heat exchanger applications
- NACE MR0175 / ISO 15156 — Resistance to sulfide stress cracking (SUS316L grade)
- Mill Test Certificates (MTC) — EN 10204 Type 3.1 available for every batch
- Third-Party Inspection (TPI) — SGS / BV / TÜV inspection available upon request
Unique Selling Points
- Engineering-Driven Design: Product specifications are refined through documented improvement analyses of real-world fan coil unit failures, ensuring that design margins address actual field conditions rather than theoretical assumptions.
- Corrosion-Free Longevity: Eliminates the risk of internal corrosion scaling that plagues copper and carbon steel coils, maintaining consistent thermal performance over the system's entire service life.
- Hygienic Surface Integrity: Low surface roughness values prevent biofilm accumulation, making the product suitable for food-grade and pharmaceutical HVAC applications without additional passivation treatments.
- Customizable Geometry: Coil diameter, tube OD, wall thickness, and uncoiled length can be tailored to specific OEM requirements, enabling seamless integration into proprietary fan coil unit designs.
- Full Traceability: Every coil is traceable to its heat number and production batch, supporting compliance with regulatory and audit requirements in regulated industries.
Note: The technical parameters presented herein are based on standard production configurations. Custom specifications, alternative grades (including duplex stainless steel such as SUS321 / SUS329), and specialized surface treatments are available upon request. Consultation with the engineering team at Wenzhou Jixing Metal Materials Co., Ltd. is recommended for project-specific applications.