Stainless Steel Coil Tube (Coiltube) for Large Temperature Difference Chilled Water Fan Coil Systems
Product Code: No. 581 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd | Category: Technical Literature & Product Reference
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous coil-form tubing product designed specifically for Large Temperature Difference (LTD) Chilled Water Terminal Systems, particularly for Fan Coil Unit (FCU) Series Connection Schemes. Unlike conventional straight-segment piping, the coil tube is supplied in continuous helical coil form, enabling seamless integration into fan coil unit heat exchangers and distribution manifolds without requiring field welding or brazing joints.
This product represents a paradigm shift in hydronic terminal design. In large temperature difference chilled water systems—where supply and return temperature differentials can reach 12–15°C or higher—the coil tube's uniform wall thickness, superior thermal conductivity, and resistance to thermal cycling make it an ideal choice for maintaining consistent heat transfer performance across extended operating cycles. The coil configuration also facilitates compact installation within fan coil unit housings, reducing footprint while maximizing heat exchange surface area.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel, Grade 304 (UNS S30408) or Grade 316 (UNS S31603), depending on service environment requirements
- Equivalent Standards: GB/T 12771, ASTM A213/A269, EN 10216-5
- Carbon Equivalent (CE): ≤ 0.04% for Grade 304; ≤ 0.03% for Grade 316L
2.2 Key Mechanical & Physical Properties
| Property | Grade 304 | Grade 316 | Test Standard |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | GB/T 228.1 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | GB/T 228.1 |
| Elongation at Break (%) | ≥ 40 | ≥ 40 | GB/T 228.1 |
| Thermal Conductivity (W/m·K, at 20°C) | 16.3 | 14.6 | ASTM E153 |
| Thermal Expansion Coefficient (×10⁻⁶/K, 20–100°C) | 17.3 | 17.1 | ASTM E228 |
| Corrosion Resistance (Pitting, ASTM G48) | Passive in most aqueous environments | Superior chloride resistance | ASTM G48 |
| Operating Temperature Range (°C) | -196 to +870 | -196 to +870 | — |
2.3 Surface Finish
- Inner Surface: Electropolished or mechanically polished to Ra ≤ 0.4 μm, ensuring laminar flow characteristics and minimizing fouling risk in chilled water circuits
- Outer Surface: Bright annealed or pickled & passivated, with optional protective coating for enhanced corrosion protection during storage and transport
3. Specifications
| Parameter | Specification / Range | Notes |
|---|---|---|
| Nominal Outer Diameter (OD) | 6.35 mm – 34.93 mm (1/4" – 1-1/4") | Custom diameters available |
| Wall Thickness | 0.5 mm – 3.0 mm | ±0.05 mm tolerance |
| Coil Inner Diameter (ID) | 100 mm – 500 mm | Depends on application and shipping constraints |
| Coil Length per Spool | 50 m – 200 m | Continuous length, no joints |
| Maximum Working Pressure | 1.6 MPa – 2.5 MPa | Hydrostatic test at 1.5× working pressure |
| Temperature Differential (ΔT) | Up to 15°C (Supply 7°C / Return 22°C typical) | Optimized for LTD systems |
| Flow Velocity (Recommended) | 0.5 – 1.5 m/s | Minimizes noise and erosion |
| Heat Transfer Coefficient | ≥ 2,500 W/m²·K | Inner surface, turbulent flow regime |
| Weight (approximate) | 0.28 – 1.85 kg/m | Depends on OD and wall thickness |
| Protective End Caps | Plastic or polyethylene caps | Prevents contamination and damage |
4. Manufacturing Process
4.1 Process Flow
- Steel Strip Sourcing & Inspection: Cold-rolled stainless steel strip is procured from certified mills and subjected to chemical composition analysis (spectrometry), mechanical testing, and surface quality inspection.
- Coil Forming (Roll Forming): The strip is fed through a series of precision-rolled dies that progressively form the flat strip into a circular tube cross-section. This cold-forming process maintains metallurgical integrity without requiring welding.
- Seam Welding (if applicable): For welded tube configurations, a high-frequency induction welding process (HFW) or laser welding is employed. The welding parameters are precisely controlled to achieve a fully fused seam with minimal heat-affected zone (HAZ).
- Heat Treatment (Annealing): Solution annealing at 1050–1150°C followed by rapid water quenching ensures full austenitic structure, eliminates residual stresses from forming, and maximizes corrosion resistance.
- Surface Treatment: Pickling and passivation (acid dipping in nitric/hydrofluoric acid blend) removes scale and contaminants. Electropolishing is applied to the inner surface for critical applications.
- Coiling: The finished tube is wound onto a precision coiling mandrel to produce the final helical coil geometry. Tension control systems ensure uniform coil pitch and prevent kinking.
- Non-Destructive Testing (NDT): Eddy current inspection (per ASTM A776) and visual examination verify seam integrity and detect wall thickness deviations.
- Hydrostatic Testing: Each coil is pressure-tested at 1.5× the maximum working pressure to confirm leak tightness.
- Packaging & Dispatch: Coils are wrapped in moisture-proof polyethylene film, secured with steel straps, and labeled with full traceability documentation.
4.2 Quality Control Checkpoints
- Raw material verification (mill certificates, chemical analysis)
- In-process dimensional inspection at forming station
- Post-annealing hardness testing (HV ≤ 200 for Grade 304)
- Final dimensional audit (OD, wall thickness, coil pitch)
- 100% hydrostatic test with pressure logging
5. Applications
5.1 Primary Application: Large Temperature Difference Chilled Water Systems
The coil tube is purpose-engineered for Large Temperature Difference (LTD) Chilled Water Terminal Systems, where the supply water temperature is typically 5–7°C and return water temperature reaches 17–22°C, creating a temperature differential (ΔT) of 12–15°C. This approach significantly reduces chilled water flow rates and pipe sizes compared to conventional systems (ΔT = 5–7°C), resulting in lower pumping energy consumption and reduced installation costs.
5.2 Fan Coil Unit (FCU) Integration
In the FCU Series Connection Scheme, multiple fan coil units are connected in series through the coil tube distribution network. The coil tube serves as:
- Heat Exchanger Coils: Formed into serpentine or spiral patterns within FCU housings to maximize heat exchange surface area in a compact volume
- Distribution Piping: Connecting multiple FCU terminals in a series configuration, leveraging the coil tube's flexibility to navigate tight installation spaces
- Manifold Branches: Fabricated into tee and branch configurations for individual unit connections
5.3 Additional Applications
- Commercial HVAC systems in office buildings, hotels, and hospitals
- Industrial process cooling circuits requiring corrosion-resistant tubing
- Food and beverage industry sanitary piping
- Pharmaceutical cleanroom HVAC distribution
- Marine and coastal environment applications (Grade 316)
- Geothermal heat exchange systems
6. Quality Certifications & Compliance
| Certification / Standard | Description | Status |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Certified |
| ISO 14001:2015 | Environmental Management System | Certified |
| GB/T 12771-2019 | Chinese National Standard for Welded Stainless Steel Tubes | Compliant |
| ASTM A269/A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes | Compliant |
| EN 10216-5 | European Standard for Welded Stainless Steel Tubes | Compliant |
| ASME B31.9 | Pressure Piping, Refrigeration and Air-Conditioning | Compliant |
| Hygienic Design (3-A / EHEDG) | Optional, for food-grade applications | Available on request |
| Mill Test Report (MTR) | Full chemical and mechanical analysis per heat number | Provided with each batch |
7. Unique Selling Points
1. Zero-Joint Continuous Coil Supply: The tube is delivered as a single continuous coil without field joints, eliminating potential leak points and reducing installation labor by up to 40% compared to segment-based piping.
2. Optimized for Large Temperature Difference (LTD) Systems: Engineered specifically for the thermal cycling demands of LTD chilled water systems (ΔT up to 15°C), with verified performance data for repeated thermal expansion and contraction cycles exceeding 100,000 cycles.
3. Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional resistance to pitting, crevice corrosion, and general aqueous corrosion, ensuring a design life exceeding 25 years in chilled water service without cathodic protection.
4. Compact Installation Footprint: The coil form factor allows for dense packing of heat exchange surface area within limited FCU housing volumes, enabling smaller unit dimensions while maintaining or improving thermal performance.
5. Energy Efficiency Contribution: By enabling LTD operation with reduced flow rates, the coil tube system reduces pumping energy consumption by 30–50% compared to conventional low-ΔT systems, contributing to overall building energy savings.
6. Full Traceability: Every coil spool is traceable to its steel mill heat number, with complete documentation of chemical composition, mechanical properties, and all manufacturing process parameters.
8. Technical Reference
This product specification is informed by the technical study and practical implementation of the "Large Temperature Difference Chilled Water Terminal — Fan Coil Unit Series Connection Scheme" (《冷冻水大温差末端——风机盘管机组串联方案》), which documents the engineering rationale, system design methodology, and field performance validation for integrating coil tube technology into next-generation hydronic terminal systems.
Manufacturer Contact: Wenzhou Jixing Metal Materials Co., Ltd — Technical Inquiry & Custom Specification Available Upon Request