Stainless Steel Coil Tube — Fan Coil Unit (FCU) Application Series
Product Code: No. 282 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Name: Stainless Steel Coil Tube (盘管 / Coiltube) — Designed for Floor Radiation Coupled Fan Coil Unit Air Conditioning Systems
1. Product Overview
The Stainless Steel Coil Tube product series manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange component specifically developed for advanced Floor Radiation Coupled Fan Coil Unit (FR-FCU) air conditioning systems. These coil tubes serve as the core heat transfer elements within fan coil units that operate in conjunction with floor radiant heating/cooling systems, enabling integrated thermal management in commercial, residential, and institutional buildings.
Based on extensive research into the performance and control optimization of floor radiation coupled fan coil tube air conditioning systems, this product line incorporates design refinements that address the unique challenges of dual-mode thermal regulation — combining sensible heat removal via fan coil tube convection with latent and radiant heat exchange through floor systems. The coil tubes are engineered to maintain optimal thermal efficiency across variable load conditions, minimize condensation risk, and ensure long-term structural integrity under continuous cyclic thermal stress.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel conforming to ASTM A213 / ASTM A269 standards
- Standard Grades: SUS304 (UNS S30400), SUS316 (UNS S31600), SUS321 (UNS S32100)
- Alternative Grades: 304L, 316L (low-carbon variants for enhanced weldability and corrosion resistance)
- Surface Finish: Mill finish, electropolished, or passivated (as specified)
2.2 Mechanical Properties
| Property | SUS304 | SUS316 | Test Standard |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ASTM A999 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ASTM A999 |
| Elongation (%) | ≥ 40 | ≥ 40 | ASTM A999 |
| Hardness (HB) | ≤ 210 | ≤ 210 | ASTM A955 |
| Thermal Conductivity (W/m·K) | 16.3 | 14.6 | — |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | — |
2.3 Corrosion Resistance
- Excellent resistance to atmospheric, chemical, and food-grade environments
- SUS316 grade provides superior chloride pitting resistance (Cr 16–18%, Ni 10–14%, Mo 2–3%)
- Passivation treatment per ASTM A380 for enhanced passive oxide layer stability
- Resistance to scaling under continuous high-temperature water circulation
3. Specifications
| Parameter | Specification / Range | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Ø 6.35 mm, 9.53 mm, 12.70 mm, 15.88 mm, 19.05 mm, 22.23 mm | ASTM A213 / A269 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm (customizable) | — |
| Coil Winding Diameter | Ø 50 mm – Ø 300 mm | — |
| Coil Length / Circumference | 0.5 m – 12 m (per coil assembly) | — |
| Tube Pitch (Row-to-Row) | 15 mm – 50 mm | ASHRAE 15 |
| Number of Rows | 1 – 6 rows (configurable) | — |
| Fin Type (if finned) | Aluminum or stainless steel plate fins; 8–14 fins per inch | — |
| End Connection | Flared, threaded (BSP/NPT), brazed, or welded | ASME B31.9 |
| Maximum Working Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) | ASME B31.9 |
| Hydrostatic Test Pressure | 2.4 MPa (standard); 3.75 MPa (reinforced) | — |
| Design Life | ≥ 25 years under normal operating conditions | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection: Ingot certification verification, spectroscopic analysis (PMI), and mechanical property testing of incoming stainless steel strip or seamless pipe stock.
- Blanking & Forming: Precision slitting and cutting of stainless steel strip to specified OD and wall thickness dimensions.
- Seamless Pipe Production (for seamless variants): Hot or cold rolling of stainless steel billets, followed by cold drawing to achieve dimensional tolerances within ±0.05 mm.
- Coil Winding: CNC-controlled bending and coiling of formed tubes onto precision mandrels to achieve uniform winding geometry, consistent bend radii (typically ≥ 3× OD), and controlled pitch spacing.
- Fin Attachment (if applicable): Slitting and mounting of aluminum or stainless steel fins onto coiled tubes using brazing or mechanical crimping methods.
- Heat Treatment: Solution annealing at 1050–1150 °C followed by controlled cooling to eliminate residual stresses and restore full austenitic microstructure.
- Pickling & Passivation: Immersion in citric acid or nitric acid solutions to remove oxide scale, followed by passivation per ASTM A380 to establish a stable chromium oxide protective film.
- End Processing: Flaring, threading, or welding of connection fittings per customer specification.
- Quality Inspection: Dimensional verification (CMM), visual inspection, helioscopic testing for seam integrity, hydrostatic pressure testing, and eddy current testing.
- Packaging & Dispatch: Protective wrapping, moisture barrier packaging, and labeling with full traceability documentation.
4.2 Key Process Controls
- Full traceability from mill certificate to finished product via batch numbering system
- In-process dimensional checks at critical manufacturing stages
- Statistical Process Control (SPC) applied to coil winding geometry parameters
- Non-destructive testing (NDT) per ASTM E309 for seam weld integrity
5. Applications
5.1 Primary Application: Floor Radiation Coupled Fan Coil Unit Systems
This product is specifically optimized for Floor Radiation Coupled Fan Coil Unit (FR-FCU) air conditioning systems, which integrate:
- Sensible heat removal via fan coil tube convection (handled by the stainless steel coil tube assembly)
- Latent heat removal and radiant cooling/heating via embedded floor piping systems
The coil tube design accounts for the unique operational characteristics of FR-FCU systems, including:
- Reduced condensation risk through optimized coil surface temperature management
- Variable speed fan compatibility with modulating valve control
- Enhanced part-load efficiency through multi-circuit coil configurations
- Thermal stratification management in dual-source heat exchange environments
5.2 Additional Applications
- Commercial HVAC: Offices, hotels, hospitals, shopping malls, and airports
- Residential HVAC: High-end residential buildings with integrated radiant-coil systems
- Industrial Process Cooling: Precision temperature control in manufacturing facilities
- Food & Beverage Industry: Cold storage, dairy processing, and food-grade cooling circuits (SUS316 grade)
- Marine & Offshore: Corrosion-resistant heat exchange in saltwater environments
- Pharmaceutical & Laboratory: GMP-compliant cleanroom temperature control
6. Quality Certifications & Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — European Conformity for HVAC components
- UL Listed — Underwriters Laboratories safety certification (where applicable)
6.2 Material & Testing Standards
- ASTM A213 / A269 — Stainless steel seamless and welded tube specifications
- ASME B31.9 — Code for pressure piping in heating and cooling systems
- ASHRAE Standard 15 — Safety standard for refrigeration systems
- EN 10216-5 — European standard for stainless steel tubes for heat exchangers
- JIS G3446 — Japanese Industrial Standard for austenitic stainless steel tubes
- GB/T 12771 — Chinese National Standard for stainless steel seamless tubes for heat exchangers
6.3 Testing & Inspection Protocol
- 100% hydrostatic pressure testing at 2.5× working pressure for a minimum of 5 seconds
- Spectroscopic chemical composition verification per ASTM E1473 (PMI)
- Visual surface inspection per ASTM A999
- Dimensional verification using coordinate measuring machine (CMM)
- Optional: Eddy current testing, ultrasonic testing, and radiographic testing per customer requirements
7. Unique Selling Points
Performance-Optimized for FR-FCU Systems: Unlike conventional coil tubes designed for standalone fan coil units, this product series is engineered with specific consideration for the thermodynamic coupling between fan coil convection and floor radiation heat exchange. Research-driven design parameters ensure optimal performance across the full range of operating conditions encountered in integrated thermal management systems.
- Superior Corrosion Resistance: Premium austenitic stainless steel grades provide exceptional longevity in humid, chemically aggressive, and marine environments — eliminating the need for galvanic protection coatings.
- Precision Geometry: CNC-controlled coil winding ensures uniform tube spacing, consistent bend radii, and minimal flow maldistribution — directly translating to enhanced heat transfer efficiency and reduced pressure drop.
- Full Traceability: Every coil tube assembly is traceable to its raw material mill certificate, providing complete supply chain transparency for quality assurance and regulatory compliance.
- Customization Capability: Flexible manufacturing parameters (OD, wall thickness, coil diameter, pitch, row count, fin configuration) enable tailored solutions for specific FR-FCU system designs.
- Thermal Fatigue Resistance: The selected alloy grades and heat treatment processes ensure resistance to thermal cycling fatigue, critical for systems experiencing frequent start-stop and load-varying operation.
- Hygienic Design: Passivated surfaces and seamless construction prevent microbial growth and biofilm formation, meeting the highest sanitary standards.
8. Technical Notes & Recommendations
- For FR-FCU systems operating in high-humidity environments (relative humidity > 70%), SUS316 grade is recommended over SUS304 to mitigate chloride-induced pitting corrosion.
- Coil tube surface temperature should be maintained above the dew point of the ambient air to prevent condensation when operating in cooling mode with floor radiation coupling.
- Recommended coolant flow velocity: 0.5 – 2.5 m/s to ensure adequate heat transfer while minimizing erosion-corrosion risk.
- Annual inspection and hydrostatic testing is recommended to maintain system integrity and performance over the design life.
- For long-term service in potable water or food-grade applications, ensure passivation treatment is renewed every 2–3 years or as specified by local regulations.
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