Stainless Steel Evaporative Coil Tube — Coiltube Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) series manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous tubing product designed primarily for refrigeration, air conditioning, and thermal exchange applications. Unlike straight-length stainless steel pipe, coil tube is supplied in pre-formed helical or serpentine configurations, enabling direct integration into evaporator, condenser, and heat exchanger assemblies without the need for on-site bending or forming. This product line is specifically optimized for evaporative coil performance, offering superior heat transfer efficiency and dehumidification capability under a wide range of operating conditions.
The coil tube product is available in multiple coil diameters, pitch configurations, and tube cross-section geometries (round, oval, and rectangular), allowing system designers to tailor hydraulic resistance, surface-to-volume ratio, and overall thermal performance to specific application requirements. The continuous coil form factor also reduces waste material and assembly labor compared to cut-and-bend fabrication methods.
Material and Properties
The coil tubes are manufactured from high-purity austenitic stainless steel grades, selected for their combination of corrosion resistance, thermal conductivity, mechanical integrity, and long-term durability in demanding environments.
Available Material Grades
- SAE 304 (UNS S30400) — The most widely used austenitic grade, offering excellent general corrosion resistance, good formability, and suitability for food-grade and HVAC applications. Chromium content of 18–20% and nickel content of 8–10.5% provide robust passive film stability.
- SAE 316 (UNS S31600) — Enhanced corrosion resistance through the addition of 2–3% molybdenum, making it ideal for applications involving chlorides, marine environments, chemical processing, and high-purity fluid handling.
- SAE 316L (UNS S31603) — Low-carbon variant of 316L with carbon content ≤0.03%, specifically designed to resist intergranular corrosion during welding, critical for coil tube assemblies requiring post-forming welding.
- SAE 321 (UNS S32100) — Titanium-stabilized austenitic grade with superior resistance to intergranular corrosion at elevated temperatures, suitable for high-temperature evaporator and condenser duty.
Key Physical and Mechanical Properties
- Density: 8.0 g/cm³
- Thermal Conductivity (at 20°C): 14–16 W/(m·K) for 304/316 grades
- Specific Heat Capacity: 0.50 J/(g·K)
- Young's Modulus: 193 GPa
- Thermal Expansion Coefficient: 16–17 × 10⁻⁶ /K
- Yield Strength (annealed): 205–310 MPa (304); 205–310 MPa (316)
- Tensile Strength (annealed): 515–720 MPa
- Maximum Operating Temperature: Up to 870°C in oxidizing atmospheres (304); up to 870°C (316)
- Lowest Service Temperature: Down to cryogenic levels (−196°C / liquid nitrogen service)
Technical Specifications
| Parameter | Specification Range | Notes |
|---|---|---|
| Tube Outer Diameter (OD) | 3.0 mm – 25.4 mm (1/8" – 1") | Custom diameters available upon request |
| Tube Wall Thickness | 0.3 mm – 1.5 mm | Thin-wall configurations for maximum heat transfer |
| Tube Cross-Section | Round, Oval, Rectangular | Non-circular profiles for compact exchanger design |
| Coil Outer Diameter (COD) | 100 mm – 600 mm | Determined by application footprint |
| Coil Pitch (Turn Spacing) | 2.0 mm – 15.0 mm | Optimized for airflow and thermal performance |
| Coil Length per Reel | 5 m – 500 m | Continuous coil; custom lengths available |
| Surface Finish | No. 1, 2B, BA (Bright Annealed), Electropolished | BA and electropolished finishes for food-grade and hygienic applications |
| Ra Surface Roughness | ≤ 0.8 μm (electropolished) | Smooth internal surface minimizes fouling and pressure drop |
| Working Pressure | Up to 4.0 MPa (40 bar) | Dependent on wall thickness and OD; verified by hydrostatic testing |
| Hydrostatic Test Pressure | 1.5 × Working Pressure | 100% inline testing; no sampling |
| Applicable Standards | ASTM A213/A269, GB/T 12771, EN 10217-7, JIS G3459 | Multi-standard compliance for global market access |
| Refrigerant Compatibility | R-134a, R-410A, R-32, R-1234yf, R-290, Ammonia (NH₃), CO₂ (R-744) | Non-reactive with all common refrigerants |
| Corrosion Resistance | Passive film stable in pH 3–12 aqueous environments | 316L grade: chloride pitting resistance > 300 ppm Cl⁻ |
| Coil Tolerance (OD) | ±0.05 mm | Tight dimensional control for brazing and expansion fitting |
| Coil Tolerance (Wall Thickness) | ±10% of nominal | Uniform wall distribution verified by ultrasonic inspection |
Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd follows a tightly controlled, multi-stage manufacturing process to ensure dimensional accuracy, metallurgical quality, and consistent surface integrity.
Process Flow
- Raw Material Procurement — Ingot or strip sourcing from certified stainless steel mills with full traceability documentation (mill test certificates per ASTM/EN standards). Incoming material undergoes spectroscopic composition verification and mechanical property testing.
- Slitting and Annealing — Wide stainless steel strip is slit to the required coil tube blank width. The strip is then solution-annealed at 1050–1100°C followed by controlled cooling to restore full austenitic microstructure and achieve the annealed (soft) condition for subsequent forming.
- Forming (Tube Milling) — The annealed strip is fed through a precision roll-forming mill where a series of forming rolls progressively bend the strip into a tubular configuration. For round tubes, the seam is closed and formed; for oval and rectangular tubes, the cross-section is shaped to the target geometry.
- Seam Welding — A high-frequency induction or TIG (Tungsten Inert Gas) welding process is applied to close the longitudinal seam. The welding parameters are continuously monitored and controlled to ensure full penetration and consistent weld bead geometry. Inert gas (argon) shielding prevents oxidation at the weld zone.
- Post-Weld Heat Treatment (if required) — For applications requiring stress relief or grain stabilization (e.g., 321 grade), a post-weld annealing cycle is performed at 870–900°C with controlled cooling.
- Coil Winding — The continuous formed and welded tube is wound into the specified coil configuration (helical coil, serpentine, or flat coil) using precision winding equipment. Coil diameter, pitch, and total length are controlled by CNC winding systems to within ±1% tolerance.
- Surface Finishing — Tubes are subjected to the specified surface treatment:
- Bright Annealing (BA): Annealing in a reducing atmosphere (endothermic gas) to produce a bright, clean, oxide-free surface.
- Electropolishing: Electrochemical dissolution of surface asperities to achieve Ra ≤ 0.8 μm, critical for hygienic and food-processing applications.
- Pickling and Passivation: Chemical removal of surface scale followed by passivation to restore the chromium oxide passive film.
- Quality Inspection — Every coil undergoes:
- 100% hydrostatic pressure testing at 1.5× working pressure
- Ultrasonic wall thickness measurement (random sampling per reel)
- Visual and dimensional inspection of OD, wall thickness, and coil geometry
- Weld seam inspection via visual or penetrant testing
- Chemical composition verification via optical emission spectrometry (OES)
- Packaging and Delivery — Coils are wrapped in protective plastic film and moisture-barrier packaging, secured on wooden pallets or steel cradles, and labeled with product identification, material grade, coil dimensions, and mill test certificate reference.
Applications
The stainless steel coil tube product line from Wenzhou Jixing Metal Materials Co., Ltd serves a broad spectrum of industrial and commercial applications where corrosion resistance, thermal performance, and long service life are critical.
Primary Application Domains
- Refrigeration and Air Conditioning (HVAC/R) — Evaporator and condenser coils for commercial refrigeration systems, supermarket display cases, walk-in cold rooms, chiller units, and rooftop air conditioning units. The coil tube's high surface-to-volume ratio and stainless steel's non-reactivity with modern refrigerants (R-410A, R-32, R-1234yf) make it an ideal choice for next-generation low-GWP (Global Warming Potential) systems.
- Industrial Heat Exchangers — Shell-and-tube and plate-and-frame heat exchanger tube bundles for chemical processing, pharmaceutical manufacturing, food and beverage processing, and power generation.
- Automotive and Transportation — Intercooler coils, evaporator assemblies, and thermal management systems for commercial vehicles, rail transit, and marine applications where resistance to salt spray and vibration is required.
- Food Processing and Dairy Equipment — Pasteurization coils, sterilization loops, and hygienic heat exchangers compliant with FDA and EHEDG (European Hygienic Engineering Design Group) standards. Electropolished finishes prevent bacterial adhesion and facilitate CIP (Clean-in-Place) procedures.
- Marine and Offshore — Seawater cooling coils, heat recovery systems, and ballast water treatment components. 316L grade provides superior resistance to chloride-induced pitting and crevice corrosion in marine environments.
- Medical and Laboratory Equipment — Cooling coils for MRI (Magnetic Resonance Imaging) systems, autoclave thermal circuits, and laboratory refrigeration units requiring non-toxic, non-magnetic, and biocompatible materials.
- Solar Thermal and Geothermal Systems — Heat collector coils and geothermal heat pump loop tubing where long-term durability in corrosive groundwater or high-temperature solar fluid is essential.
Performance Characteristics in Evaporative Coil Applications
Based on experimental research into evaporative coil heat transfer and dehumidification characteristics, the coil tube geometry provides distinct advantages over straight pipe configurations:
- Enhanced Heat Transfer Coefficient — The helical curvature induces secondary flow (Dean vortices) within the tube, disrupting the thermal boundary layer and increasing the internal convective heat transfer coefficient by 15–30% compared to straight tube of equivalent diameter and flow rate.
- Improved Dehumidification Efficiency — The compact coil arrangement maximizes the effective heat exchange surface area per unit volume, enabling deeper air dew-point depression and higher latent heat removal rates in air-cooled evaporator coils.
- Reduced Pressure Drop Sensitivity — While coil geometry inherently introduces additional frictional pressure drop due to curvature, the optimized pitch and tube diameter selection by Wenzhou Jixing balances thermal performance against hydraulic resistance, achieving a favorable performance-to-pressure-drop ratio.
- Uniform Temperature Distribution — The continuous coil winding promotes more uniform refrigerant distribution across the coil face, reducing localized hot/cold spots and improving overall system COP (Coefficient of Performance).
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a rigorous quality management system and holds the following certifications and complies with the following international standards:
Quality Management Certifications
- ISO 9001:2015 — Quality Management Systems (QMS), certifying adherence to international best practices in quality assurance, process control, and continuous improvement.
- ISO 14001:2015 — Environmental Management Systems (EMS), demonstrating commitment to environmentally responsible manufacturing practices, waste minimization, and sustainable resource utilization.
- ISO 45001:2018 — Occupational Health and Safety Management Systems, ensuring workplace safety and worker well-being throughout the manufacturing process.
Product Standards Compliance
- ASTM A213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature Service
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- GB/T 12771 — Chinese National Standard for Welded Stainless Steel Tubes for Fluid Transport
- EN 10217-7 — European Standard for Non-Alloy and Alloy Steel Tubes for Mechanical, Thermal, and Technical Uses — Part 7: Austenitic Stainless Steel Tubes