Stainless Steel Coil Tube for Ultra-Thin Fan Coil Units (GBFP Series)
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Product No. 1325) is a precision-engineered stainless steel tubing product specifically designed for integration into GBFP Ultra-Thin Fan Coil Unit (Fan Coil Unit, FCU) assemblies. These coil tubes serve as the core heat exchange elements within compact air conditioning and ventilation systems, facilitating efficient thermal transfer between the refrigerant medium and ambient air.
This product line represents a specialized category of stainless steel coil tubing optimized for ultra-thin form-factor HVAC applications, where spatial constraints demand maximum heat exchange performance within minimal footprint dimensions. The coil tubes are engineered to meet the stringent requirements outlined in the GBFP Ultra-Thin Fan Coil Unit technical framework, ensuring reliable performance in commercial, residential, and industrial climate control environments.
2. Material & Properties
2.1 Base Material
The coil tubes are fabricated from high-grade stainless steel, with the following material specifications:
- Primary Grades: AISI 304 (UNS S30408), AISI 316 (UNS S31603), and AISI 321 (UNS S32101)
- Composition (304 Grade): Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤2.0%, Carbon (C) ≤0.08%, Silicon (Si) ≤1.0%
- Composition (316 Grade): Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%, Carbon (C) ≤0.08%
- Surface Finish: 2B, BA (Bright Annealed), or No. 4 (Brushed) — selectable per application requirement
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥515 MPa (304), ≥515 MPa (316)
- Yield Strength: ≥205 MPa (304), ≥205 MPa (316)
- Elongation: ≥40% (304), ≥35% (316)
- Hardness: ≤201 HB (Annealed condition)
- Operating Temperature Range: −196°C to +870°C (304 grade); −196°C to +870°C (316 grade)
- Thermal Conductivity: 16.3 W/(m·K) at 100°C (304 grade)
2.3 Corrosion Resistance
- Pitting Resistance (PREN): ≥18 (304 grade); ≥24 (316 grade)
- Intergranular Corrosion: Compliant with ASTM A262 Practice E
- Chloride Resistance: Superior performance in humid, coastal, and chemically aggressive environments
- Scaling Resistance: Maintains surface integrity under prolonged high-temperature operation
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Product No. | 1325 | Wenzhou Jixing Internal Catalog |
| Outer Diameter (OD) | 6.35 mm (¼"), 9.53 mm (⅜"), 12.7 mm (½") | ASME B36.19M |
| Wall Thickness | 0.5 mm – 1.2 mm (Ultra-thin wall option available) | ASTM A269 / A270 |
| Tube Length (Per Coil) | Up to 1,000 m per continuous coil | Manufacturer Specification |
| Coil Inner Diameter | 300 mm – 600 mm (configurable) | Customer Requirement |
| Bend Radius | ≥3× OD (minimum bend radius) | ISO 1127 |
| Pressure Rating | Up to 1.6 MPa (16 bar) at 20°C | ASME B31.9 |
| Dimensional Tolerance | ±0.05 mm (OD); ±10% (wall thickness) | ASTM A269 |
| Surface Roughness | Ra ≤ 0.8 μm (BA finish); Ra ≤ 1.6 μm (2B finish) | ISO 4287 |
| Delivery Form | Coiled / Coil-wound continuous tubing | — |
| Protective Coating | Polyethylene (PE) wrap / VCI paper wrap (optional) | ISO 21600 |
| Applicable System | GBFP Ultra-Thin Fan Coil Unit | GB/T 19232 / GBFP Series |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Selection & Inspection: Virgin stainless steel strip or seamless tube blanks are sourced from certified mills. Incoming material undergoes spectrographic analysis (OES), mechanical testing, and visual surface inspection to confirm compliance with ASTM A269/A270 specifications.
- Coil Winding & Forming: The stainless steel tube is wound into a continuous coil configuration using precision CNC-controlled winding equipment. The winding process maintains uniform tension to prevent distortion, kinking, or ovality exceeding tolerance limits.
- Heat Treatment (if required): Solution annealing at 1050°C–1150°C followed by rapid quenching to achieve full austenitic microstructure, maximize corrosion resistance, and relieve residual stresses introduced during forming.
- Pickling & Passivation: The coil tube surface is treated with nitric acid-hydrofluoric acid (HNO₃/HF) pickling solution to remove oxide scale, followed by passivation treatment to restore the passive chromium oxide film. This ensures long-term corrosion protection.
- Precision Dimensional Verification: Each coil undergoes automated dimensional measurement including outer diameter, wall thickness, ovality, and coil geometry using laser gauging systems and coordinate measurement machines (CMM).
- Hydrostatic / Pneumatic Pressure Testing: Every coil tube is subjected to hydrostatic pressure testing at 1.5× the rated working pressure to verify structural integrity and freedom from leaks or wall defects.
- Surface Protection & Packaging: The finished coil tubes are wrapped in protective PE film or VCI (Vapor Corrosion Inhibitor) paper to prevent surface damage and moisture exposure during storage and transportation. Coils are secured on wooden pallets with steel strapping.
4.2 Quality Control Milestones
- Incoming material certification review (Mill Test Certificate, MTC)
- In-process dimensional checks at critical winding stations
- 100% pressure testing prior to release
- Final visual and dimensional inspection before packaging
- Batch traceability maintained via unique heat lot numbers
5. Applications
5.1 Primary Application: GBFP Ultra-Thin Fan Coil Units
The stainless steel coil tubes are the primary heat exchange medium within GBFP Ultra-Thin Fan Coil Units, which are compact HVAC terminal units designed for concealed ceiling installations in commercial and residential buildings. The coil tubes facilitate the transfer of thermal energy between circulating water (heating or chilled water) and the air stream driven by the internal fan.
5.2 Expanded Application Domains
- Commercial HVAC Systems: Office buildings, hotels, shopping centers, and hospitals requiring space-constrained climate control solutions
- Residential Air Conditioning: Ducted and ductless mini-split systems in high-end residential developments
- Industrial Process Cooling: Precision temperature control in manufacturing facilities, data centers, and clean rooms
- Marine & Coastal Environments: 316-grade coil tubes provide exceptional resistance to saltwater corrosion in marine HVAC applications
- Food & Pharmaceutical Processing: Hygienic-grade coil tubes meet FDA and GMP requirements for sanitary air handling systems
- Automotive & Transportation: Lightweight, corrosion-resistant coil tubing for vehicle climate control systems
6. Quality Certifications & Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System (QMS) certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System (EMS) compliance
- CE Marking — Conformity with European Health, Safety, and Environmental Protection standards
- RoHS Compliance — Restriction of Hazardous Substances directive (EU 2011/65/EU)
- REACH Compliance — Registration, Evaluation, Authorisation and Restriction of Chemicals (EC 1907/2006)
6.2 Material & Performance Standards
- ASTM A269 / A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severely Corrosive Services
- ASTM A270 / A270M — Standard Specification for Austenitic Stainless Steel Tubing, Seamless, Welded, and Heavy Welded
- ASME B36.19M — Dimensions for Stainless Steel Tubing
- ASME B31.9 — Pressure Piping, Process Piping
- GB/T 19232 — Chinese National Standard for Fan Coil Units
- GB/T 14976 — Chinese National Standard for Seamless Stainless Steel Tubes
6.3 Testing & Verification
- Mechanical Testing: Tensile testing, hardness testing (Rockwell B), and impact testing (Charpy V-Notch) per ASTM E8/E8M
- Chemical Analysis: Spectrographic composition verification per ASTM E1/A1
- Corrosion Testing: Salt spray testing (ASTM B117, 1000+ hours), intergranular corrosion testing (ASTM A262 Practice E), and pitting corrosion testing (ASTM G48)
- Dimensional Inspection: 100% automated OD and wall thickness gauging; sample-based CMM verification
- Pressure Testing: Hydrostatic testing at 1.5× working pressure for minimum 30 seconds per coil
7. Unique Selling Points
- Ultra-Thin Wall Engineering: Proprietary manufacturing capability enables wall thicknesses as low as 0.5 mm while maintaining structural integrity and pressure resistance, maximizing heat transfer efficiency within the compact GBFP unit envelope.
- Superior Corrosion Longevity: Stainless steel construction eliminates the risk of internal rust formation and scaling that plagues carbon steel alternatives, extending service life to 20+ years in demanding environments.
- HVAC-Optimized Geometry: Coil tube dimensions and winding parameters are specifically calibrated for the GBFP ultra-thin fan coil unit platform, ensuring optimal airflow distribution and thermal performance.
- Full Traceability: Every coil tube is traceable to its mill heat lot, enabling complete supply chain transparency and quality accountability.
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd offers flexible customization of OD, wall thickness, coil geometry, surface finish, and packaging to meet specific OEM and project requirements.
- Hygienic & Food-Safe: Available in electropolished and sanitary-grade finishes suitable for pharmaceutical, food processing, and medical facility HVAC applications.
Technical Note: The GBFP Ultra-Thin Fan Coil Unit platform represents the next generation of compact HVAC terminal units, where the integration of precision-engineered stainless steel coil tubes is critical to achieving high thermal efficiency within severely constrained installation spaces. Wenzhou Jixing Metal Materials Co., Ltd's Product No. 1325 coil tubes are purpose-developed to meet this exacting engineering challenge.