Stainless Steel Coil Tube — Model No. 365 (Fan Coil Unit Grade)
1. Product Overview
The Stainless Steel Coil Tube (Model No. 365) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous coil tube designed primarily for integration into cabinet-type fan coil unit (FCU) assemblies as defined by the Chinese national industry standard JB/T 9066—1999 (Thermal Performance Test Method for Cabinet Fan Coil Units). This product is supplied in continuous coil form, enabling high-efficiency downstream processing including straightening, cutting, bending, and brazing operations without compromising metallurgical integrity or dimensional accuracy.
As a critical heat exchange component within air-conditioning and ventilation (HVAC) systems, the coil tube must exhibit excellent thermal conductivity, long-term corrosion resistance, and dimensional stability under cyclic thermal loading conditions. Wenzhou Jixing Metal Materials Co., Ltd. has developed this product line specifically to meet the rigorous thermal performance requirements outlined in JB/T 9066—1999, ensuring reliable heat transfer efficiency across the full operating range of fan coil unit installations.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 / SUS 304 (1.4301) — Austenitic stainless steel with optimal balance of corrosion resistance and formability; the primary grade used for general-purpose coil tubes in indoor HVAC applications.
- AISI 316 / SUS 316 (1.4401) — Molybdenum-enhanced austenitic stainless steel offering superior resistance to chloride-induced pitting and crevice corrosion; recommended for coastal or high-humidity environments.
- AISI 321 / SUS 321 (1.4541) — Titanium-stabilized austenitic stainless steel providing enhanced resistance to intergranular corrosion during brazing and welding operations.
2.2 Key Material Properties
- Thermal Conductivity (at 20°C): 16.3 W/(m·K) for Grade 304; 14.6 W/(m·K) for Grade 316
- Specific Heat Capacity (at 20°C): 502 J/(kg·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /K
- Maximum Service Temperature: 870°C (Grade 304); 870°C (Grade 316)
- Corrosion Resistance: Excellent resistance to atmospheric, freshwater, and mild chemical environments; Grade 316 provides enhanced resistance to chlorides and acidic condensates commonly encountered in HVAC condensate drainage systems.
- Mechanical Properties: Yield strength ≥ 205 MPa (annealed condition); Ultimate tensile strength ≥ 515 MPa; Elongation ≥ 40%
3. Specifications
| Parameter | Specification | Tolerance / Standard |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm, 6.35 mm, 8.0 mm, 9.53 mm, 10.0 mm, 12.7 mm | ±0.05 mm (per ASTM A269) |
| Wall Thickness (WT) | 0.40 mm, 0.50 mm, 0.60 mm, 0.80 mm, 1.00 mm | ±0.03 mm |
| Inside Diameter (ID) | 5.0 mm – 11.9 mm (derived) | ±0.08 mm |
| Coil Length | 10 m – 100 m per coil (customizable) | As per customer requirement |
| Coil Inner Diameter (Coil ID) | 150 mm – 600 mm | ±10 mm |
| Surface Finish | Bright annealed (BA), Polished (Ra ≤ 0.8 μm), Matte | Per ASTM A269 / ASTM A270 |
| End Condition | Plain, Beveled, Flanged, or Threaded | As specified |
| Heat Treatment | Full annealing at 1050°C – 1100°C followed by controlled cooling | Per ASTM A269 |
| Chemical Composition | C ≤ 0.08%, Cr ≥ 18.0%, Ni ≥ 8.0% (Grade 304) | Per ASTM A240 / GB/T 4237 |
| Corrosion Testing | PASS — ASTM A967 passivation treatment applied | Per ASTM A967 |
| Pressure Test | Hydrostatic test at 1.5× working pressure for 30 minutes | Per ASME B31.9 |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip is sourced from certified mill suppliers and subjected to incoming inspection including chemical composition analysis (via Optical Emission Spectroscopy — OES), mechanical property verification, and surface quality assessment.
- Slitting & Coil Formation: The cold-rolled strip is slit to the required width using precision slitting lines with automatic tension control systems. The slit strip is then formed into a coil with controlled edge quality to prevent surface defects during subsequent forming operations.
- Tube Forming (ERW / Induction Welding): The coil strip is fed through a high-precision tube forming die set. Edge preparation (beveling and cleaning) ensures uniform weld quality. Electrical Resistance Welding (ERW) or induction welding is employed to form the longitudinal seam, achieving full metallurgical fusion with minimal heat-affected zone (HAZ).
- Heat Treatment (Annealing & Pickling): The formed tubes undergo continuous annealing in a controlled-atmosphere furnace (protective gas environment — N₂ or H₂/N₂ mixture) at temperatures between 1050°C and 1100°C. This eliminates welding residual stresses, restores full austenitic microstructure, and ensures uniform mechanical properties. Post-annealing pickling and passivation treatment removes oxide scale and establishes a protective chromium oxide passive film on the surface.
- Sizing & Straightening: Multi-roller sizing and straightening equipment ensures dimensional accuracy of the outer diameter, wall thickness, and straightness within specified tolerances. Straightness is maintained at ≤ 0.5 mm/m.
- Surface Finishing: Depending on the application, tubes may undergo electropolishing, mechanical polishing (Ra ≤ 0.8 μm), or passivation treatment to achieve the required surface finish grade.
- Quality Inspection & Testing: Comprehensive inspection protocols include dimensional measurement (laser OD measurement), hydrostatic pressure testing, eddy current testing (ECT) for weld seam integrity, and visual inspection of surface quality.
- Coiling & Packaging: Finished tubes are coiled to specified coil diameters and lengths, wrapped with protective film, and packaged in wooden or steel crates with moisture-absorbing desiccants for shipping and storage.
4.2 Process Control Highlights
- Continuous online monitoring of weld seam quality via ultrasonic testing (UT) during the forming operation.
- Real-time dimensional feedback control with automatic correction of tube OD and wall thickness deviations.
- Atmosphere-controlled annealing to prevent carbon pickup and decarburization, maintaining full austenitic microstructure.
- Each production batch is traceable via unique heat number and coil identification for full quality traceability.
5. Applications
5.1 Primary Application — Fan Coil Units (FCU)
The coil tube is the core heat exchange element in cabinet-type fan coil units as specified in JB/T 9066—1999. In these systems, the coil tube serves as the primary medium for heat transfer between the circulating fluid (chilled water or hot water) and the ambient air stream. The thermal performance of the fan coil unit — including total cooling capacity, sensible cooling capacity, heating capacity, and air-side heat transfer coefficient — is directly dependent on the material properties and dimensional accuracy of the coil tube.
Key performance parameters evaluated under JB/T 9066—1999 include:
- Total Cooling Capacity (QT): Measured under standard conditions (indoor 27°C DB / 19°C WB, outdoor 35°C DB / 24°C WB, water inlet 7°C)
- Sensible Cooling Capacity (QS): Reflecting the dry-bulb temperature reduction capability
- Heating Capacity (QH): Measured with water inlet temperature at 50°C and indoor air at 20°C DB
- Air-Side Heat Transfer Coefficient (hair): Indicative of the effective heat exchange surface area and fin-tube configuration efficiency
- Water-Side Pressure Drop (ΔPw): Influenced by the internal flow characteristics of the coil tube
5.2 Additional Applications
- Commercial HVAC Systems: Chilled water distribution piping, condenser and evaporator coils, air handling units (AHU), and rooftop units.
- Industrial Process Cooling: Heat exchangers for chemical processing, pharmaceutical manufacturing, and food processing equipment requiring sanitary-grade stainless steel contact surfaces.
- Automotive Air Conditioning: Evaporator and condenser coil tubes for passenger vehicles and commercial vehicles.
- Refrigeration Systems: Intermediate and low-temperature refrigeration coil assemblies for cold storage facilities and industrial refrigeration plants.
- Domestic Appliances: Heat exchanger coils for water heaters, dishwashers, and range hoods.
6. Quality Certifications & Compliance
6.1 Applicable Standards
- JB/T 9066—1999 — Cabinet Fan Coil Unit — Thermal Performance Test Method (Chinese National Industry Standard)
- GB/T 14976—2012 — Seamless Stainless Steel Tubes for Fluid Transport (Chinese National Standard)
- GB/T 4237—2015 — Stainless Steel Plates, Sheets and Strips (Chinese National Standard)
- ASTM A269/A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Similar Severely Corrosive Services
- ASTM A270/A270M — Standard Specification for General Requirements for Seamless and Welded Austenitic Stainless Steel Tubing
- ASTM A967 — Standard Practice for Chemical Cleaning and Passivation of Stainless Steel Parts
- EN 10217-7 — Non-alloy and Alloy Steel Tubes for Mechanical and Technical Purposes — Welded Tubes — Part 7: Tubes of Austenitic Steels for General Purposes
- ISO 3506 — Non-ferrous Metal Fasteners — General Requirements (for associated fittings)
6.2 Quality Management System
- ISO 9001:2015 — Quality Management System certification for consistent product quality and customer satisfaction.
- ISO 14001:2015 — Environmental Management System certification for environmentally responsible manufacturing practices.
- CE Marking — Conformity with European directives for market access in the European Economic Area.
- Mill Test Certificates (MTC) — EN 10204 Type 3.1 certificates provided for each production batch, including chemical composition analysis, mechanical property test results, and dimensional inspection records.
6.3 Inspection & Testing Protocols
- Chemical Composition Analysis: Verified by Optical Emission Spectroscopy (OES) and/or wet chemical analysis per ASTM E1450.
- Mechanical Testing: Tensile testing per ASTM E8/E8M; hardness testing per ASTM E10.
- Dimensional Inspection: Laser-based outer diameter measurement, ultrasonic wall thickness gauging, and straightness measurement per ASTM E1025.
- Weld Seam Integrity: Eddy current testing (ECT) per ASTM E2785 and/or radiographic testing (RT) per ASTM E94.
- Corrosion Resistance Testing: Salt spray testing per ASTM B117 (minimum 500 hours without pitting for Grade 304; 1000 hours for Grade 316); intergranular corrosion testing per ASTM A262 Practice E.
- Hydrostatic Pressure Testing: Performed at 1.5× the maximum design working pressure with a minimum hold time of 30 seconds per meter of tube length.
7. Unique Selling Points
Wenzhou Jixing Metal Materials Co., Ltd. distinguishes its Model No. 365 Stainless Steel Coil Tube through the following competitive advantages:
- Thermal Performance Optimization: Specifically engineered to meet and exceed the thermal performance benchmarks defined in JB/T 9066—1999, ensuring high-efficiency heat transfer in fan coil unit applications with verified total cooling capacity and sensible cooling capacity performance.
- Superior Corrosion Resistance: Full passivation treatment per ASTM A967 provides enhanced resistance to condensate-induced corrosion, extending service