Stainless Steel Coil Tube (Coiltube) — HVAC & Industrial Heat Exchange Application
Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1100) manufactures high-performance stainless steel coil tubes designed for use in Fan Coil Units (FCUs), Dry Coil Systems (DCS), and industrial heat exchange applications. These coil tubes are engineered to deliver superior thermal efficiency, extended service life, and resistance to corrosion in demanding environmental conditions.
1. Product Overview
The stainless steel coil tube is a precisely formed tubular component wound into a continuous helical or serpentine configuration, serving as the primary heat transfer element in air handling and thermal management systems. Unlike conventional copper or aluminum coil tubes, stainless steel variants offer enhanced mechanical durability, resistance to chemical attack, and compatibility with a broader range of refrigerants and working fluids.
This product line addresses the critical challenge identified in advanced dry coil system design — specifically, the need for accurate cooling capacity correction in fan coil units operating under variable load and partial-load conditions. The coil tube geometry, wall thickness, and material selection directly influence the heat transfer coefficient and overall system performance envelope.
2. Material & Properties
2.1 Material Composition
Wenzhou Jixing Metal Materials Co., Ltd. offers coil tubes fabricated from the following stainless steel grades, each selected for specific application requirements:
- AISI 304 (UNS S30400) — The most widely used austenitic stainless steel, offering excellent general corrosion resistance and formability. Suitable for standard HVAC and commercial building applications.
- AISI 316 (UNS S31600) — Enhanced corrosion resistance due to molybdenum (Mo) addition (2–3%). Recommended for coastal environments, chemical processing, and high-humidity installations.
- AISI 316L (UNS S31603) — Low-carbon variant of 316L providing superior weldability and resistance to intergranular corrosion. Ideal for welded coil assemblies and cryogenic applications.
- AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade offering excellent resistance to high-temperature scaling and intergranular corrosion in temperatures up to 870°C (1600°F).
2.2 Key Material Properties
| Property | AISI 304 | AISI 316 | AISI 316L | AISI 321 |
|---|---|---|---|---|
| Carbon (C) Max % | 0.08 | 0.08 | 0.03 | 0.08 |
| Chromium (Cr) % | 18.0–20.0 | 16.0–18.0 | 16.0–18.0 | 17.0–19.0 |
| Nickel (Ni) % | 8.0–10.5 | 10.0–14.0 | 10.0–14.0 | 9.0–12.0 |
| Molybdenum (Mo) % | — | 2.0–3.0 | 2.0–3.0 | — |
| Titanium (Ti) % | — | — | — | 5×(C+N)–0.70 |
| Tensile Strength (MPa) Min | 515 | 515 | 485 | 515 |
| Yield Strength (MPa) Min | 205 | 205 | 170 | 205 |
| Thermal Conductivity (W/m·K) @ 20°C | 16.3 | 14.6 | 14.6 | 15.1 |
| Density (kg/m³) | 8000 | 8000 | 8000 | 8000 |
| Maximum Service Temperature (°C) | 870 | 870 | 870 | 870 |
3. Technical Specifications
| Specification Parameter | Standard Value / Range | Reference Standard |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 12.7 mm (1/8" – 1/2") | ASME B36.19M / GB/T 14976 |
| Wall Thickness | 0.3 mm – 1.5 mm | ASTM A269 / ASTM A213 |
| Coil Length (Continuous) | 5 m – 200 m (customizable) | — |
| Coil Diameter (Wound) | 100 mm – 800 mm | — |
| Bend Radius (Minimum) | ≥ 3× OD | — |
| Surface Finish | Mill Finish / Brushed / Polished (Ra ≤ 0.4 μm) | ASTM A480 |
| Operating Pressure (Max) | 1.6 MPa – 4.0 MPa (PN16 – PN40) | EN 10217 |
| Operating Temperature Range | -196°C to +870°C | — |
| Tolerance on OD | ±0.05 mm – ±0.10 mm | ASTM A213 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Heat Treatment | Solution Annealed (1050°C – 1150°C) + Water Quench | ASTM A213 |
| Packaging | Coiled on wooden reels with moisture-proof wrapping | — |
4. Manufacturing Process
The production of Wenzhou Jixing Metal Materials Co., Ltd. stainless steel coil tubes follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and consistent performance:
- Raw Material Inspection: Incoming stainless steel strips or seamless tubes are subjected to spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition against ASTM and GB standards. Heat number traceability is maintained throughout the production cycle.
- Coil Winding / Helical Forming: Straight tube stock is fed through precision CNC (Computer Numerical Control) bending machines that form the tube into the required coil geometry. The bending process employs mandrel-assisted forming to prevent ovalization, wrinkling, or wall thinning at bend points.
- Heat Treatment (Solution Annealing): Formed coils undergo solution annealing at temperatures between 1050°C and 1150°C followed by rapid water quenching. This process dissolves carbide precipitates, relieves residual stresses, and restores full corrosion resistance and ductility.
- Surface Finishing: Coils may undergo pickling and passivation treatment (using nitric acid or citric acid solutions) to remove oxide scale and form a protective chromium oxide passive film. Optional polishing achieves surface roughness values as low as Ra 0.2 μm.
- Non-Destructive Testing (NDT): Each production batch undergoes 100% eddy current testing (ECT) for wall thickness verification and surface defect detection. Select batches receive ultrasonic testing (UT) for subsurface flaw detection and hydrostatic pressure testing at 1.5× the maximum operating pressure.
- Dimensional Inspection: Outer diameter, wall thickness, and coil geometry are verified using laser micrometers and CMM (Coordinate Measuring Machine) systems. Sampling protocols follow ASTM E29 statistical acceptance criteria.
- Packaging & Dispatch: Finished coils are wound onto protective wooden or steel reels, wrapped in moisture-absorbent desiccant paper and PE (Polyethylene) film, and labeled with heat number, material grade, dimensions, and certification documentation.
5. Applications
5.1 HVAC & Dry Coil Systems
The primary application domain for this coil tube product is in Fan Coil Units (FCUs) and Dry Coil Systems (DCS) used in commercial and industrial air conditioning. In dry coil system design, the coil tube serves as the evaporator or condenser element where accurate cooling capacity correction is critical. The stainless steel construction eliminates the risk of galvanic corrosion between dissimilar metals and ensures stable thermal performance across varying part-load conditions.
Technical Note: In dry coil system design, the cooling capacity of fan coil units must be corrected for actual operating conditions, including air-side wet-bulb temperature, air velocity, and coil approach temperature. The geometric and material properties of the coil tube — particularly its surface area-to-volume ratio, wall thermal resistance, and fin efficiency — are fundamental parameters in the capacity correction methodology. Wenzhou Jixing's precisely manufactured coil tubes provide the dimensional consistency required for reliable thermal modeling and capacity prediction.
5.2 Additional Applications
- Industrial Heat Exchangers: Shell-and-tube heat exchangers in chemical processing, food and beverage, and pharmaceutical industries where corrosion resistance is paramount.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration, cryogenic systems, and cold storage facilities.
- Automotive & Transportation: Intercooler coils, exhaust heat recovery systems, and fuel cell cooling circuits.
- Power Generation: Condenser tubes and steam recovery coils in power plants and combined heat and power (CHP) systems.
- Marine & Offshore: Seawater-cooled heat exchangers where resistance to chloride-induced pitting and crevice corrosion is essential.
- Water Treatment: Ultrafiltration and reverse osmosis (RO) systems requiring hygienic-grade tubing.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and certification frameworks to ensure product conformity with international standards:
| Certification / Standard | Scope of Application |
|---|---|
| ISO 9001:2015 | Quality Management System — Full production process coverage |
| ISO 14001:2015 | Environmental Management System — Sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health & Safety Management |
| CE Marking (EU) | European Conformity — Pressure Equipment Directive (PED 2014/68/EU) |
| EN 10204 3.1 | Inspection Certificate — Material and dimensional test reports |
| ASTM A213 / A269 | Material specification compliance for seamless stainless steel tubes |
| GB/T 14976 / GB/T 13296 | Chinese national standards for seamless steel tubes |
| NORSOK M-650 | Oil and gas industry — Offshore equipment material requirements (available upon request) |
7. Unique Selling Points
- Precision Geometry for Thermal Modeling Accuracy: Tight dimensional tolerances (±0.05 mm on OD) enable engineers to perform reliable heat transfer calculations and cooling capacity corrections in fan coil unit design, reducing design margins and optimizing system performance.
- Superior Corrosion Resistance vs. Copper/Aluminum: Stainless steel coil tubes eliminate galvanic corrosion risks in mixed-metal heat exchanger assemblies and withstand aggressive working fluids (including ammonia, brines, and chemical solutions) that would degrade copper or aluminum alternatives.