Stainless Steel Coil Tube (Coil Tube) — HVAC & Heating Applications
Product Overview
The Stainless Steel Coil Tube (catalog reference No. 341) is a precision-engineered continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for integration into residential and commercial heating systems, including Fan Coil Units (FCUs) and Hydronic Floor Heating Terminals. The coil tube serves as the primary heat exchange medium, transferring thermal energy from the circulating fluid (water or glycol solution) to the conditioned air or floor radiant surface.
Based on extensive literature study regarding the "Analysis of Residential Heating Load Bearing Rate of Fan Coil Units and Floor Heating Terminals," it has been established that the thermal performance, durability, and hydraulic efficiency of the coil tube directly determine the heating load bearing capacity of the terminal unit. Wenzhou Jixing Metal Materials Co., Ltd leverages advanced metallurgical expertise to produce coil tubes that maximize heat transfer efficiency while maintaining structural integrity under prolonged thermal cycling conditions.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, and mechanical strength. The material grade is chosen to withstand the corrosive effects of water treatment chemicals, dissolved oxygen, and the thermal stress inherent in continuous heating applications.
- Base Material: Austenitic Stainless Steel (grades 304 / 316L conforming to ASTM A269 / EN 10217-7)
- Corrosion Resistance: Excellent resistance to pitting and crevice corrosion in aqueous environments; suitable for both potable water and closed-loop hydronic systems
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, providing efficient heat transfer between the working fluid and the external surface
- Mechanical Strength: Tensile strength ≥ 515 MPa (Grade 304); yield strength ≥ 205 MPa; elongation ≥ 40%
- Temperature Range: Operational range of −196°C to +870°C; suitable for all residential heating water temperatures (typically 40–80°C)
- Surface Finish: Mill finish or electropolished (Ra ≤ 0.4 μm) to minimize internal flow resistance and biofilm formation
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coil Tube) | — |
| Catalog No. | 341 | — |
| Outer Diameter (OD) | 8 mm, 10 mm, 12 mm, 14 mm, 16 mm (custom available) | ASTM A269 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 1.5 mm (tolerance ±0.05 mm) | ASTM A269 / EN 10217-7 |
| Coil Length | Continuous coil; 5 m – 100 m per coil (configurable) | Manufacturer specification |
| Material Grade | SUS 304 / SUS 316L / 304L | ASTM A240 / ASTM A270 |
| Surface Treatment | Mill finish / Electropolished / Passivated | — |
| Heat Treatment | Solution annealed (1050°C – 1150°C, water quenched) | ASTM A240 |
| Hydrostatic Test | 1.5 × working pressure, minimum 5 seconds | ASTM A269 |
| Dimensional Tolerance | OD: ±0.05 mm; Wall: ±0.05 mm | GB/T 12771 |
| Packaging | Wooden pallet with moisture-proof wrapping; coil secured with steel bands | ISO 4180 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical homogeneity, and surface quality:
- Slab Preparation: Virgin stainless steel slab is produced via the Basic Oxygen Furnace (BOF) or Electric Arc Furnace (EAF) route, followed by Continuous Casting (CC) into semi-finished slabs. Chemical composition is verified by Optical Emission Spectroscopy (OES) to ensure conformity with ASTM/EN specifications.
- Hot Rolling: The slab is reheated to 1150°C–1250°C and hot-rolled into a seamless tube坯 (tube billet) or pierced into a hollow tube form via the Plattner piercing or Leavitt piercing process.
- Cold Drawing / Cold Reduction: The hot-rolled tube undergoes precision cold drawing through a series of tungsten carbide (WC) dies to achieve the final OD and wall thickness with tight tolerances (±0.05 mm). This process also induces beneficial strain hardening, improving mechanical properties.
- Solution Annealing: The cold-worked tube is solution-annealed at 1050°C–1150°C followed by rapid water quenching. This eliminates residual stresses, restores full ductility, and precipitates a uniform passive chromium oxide layer (Cr₂O₃), ensuring maximum corrosion resistance.
- Surface Finishing: Electropolishing or mechanical polishing is applied to achieve a surface roughness of Ra ≤ 0.4 μm, reducing internal friction losses and enhancing heat transfer efficiency. Chemical passivation (citric acid or nitric acid treatment) further stabilizes the passive film.
- Coiling: The finished tube is wound into a continuous coil on a precision coiling machine with controlled tension to prevent deformation, kinking, or surface damage. Coil dimensions are optimized for downstream processing (bending, finning, or direct installation).
- Quality Inspection: Each coil undergoes Eddy Current Testing (ECT) for wall thickness verification, Hydrostatic Pressure Testing for leak integrity, and Visual Inspection for surface defects. Spectrographic analysis confirms material grade compliance.
Applications
The stainless steel coil tube finds extensive application in thermal systems where reliability, longevity, and hygiene are paramount. Key application areas include:
- Fan Coil Units (FCUs): The coil tube forms the core heat exchange element within fan coil units, where it absorbs or rejects heat from circulating water to condition indoor air. Literature analysis confirms that FCUs typically bear 40–60% of the total residential heating load in mixed-mode systems, making the coil tube's thermal performance critical to overall system efficiency.
- Hydronic Floor Heating Systems: The coil tube is embedded within floor screed layers to provide radiant floor heating. The stainless steel material offers superior longevity (50+ years) compared to copper or aluminum alternatives, resisting internal corrosion from oxygen ingress and chloride contamination.
- Heat Exchangers and Radiators: Used in industrial and commercial heat exchangers where high-temperature, high-pressure conditions demand exceptional material integrity.
- Refrigeration and HVAC Systems: Serves as refrigerant tubing in heat pumps, chiller units, and air conditioning systems where the corrosion resistance of austenitic stainless steel prevents system failure.
- Domestic Hot Water Systems: Employed in instant water heaters and thermal storage tanks where hygienic requirements mandate corrosion-free, non-leaching materials.
Literature Insight: Studies on residential heating load distribution indicate that the coil tube's surface area-to-volume ratio, wall thickness, and fin configuration are the primary determinants of terminal unit efficiency. Wenzhou Jixing Metal Materials Co., Ltd optimizes these parameters to ensure that the coil tube delivers consistent thermal performance across the full range of operating conditions, thereby maximizing the heating load bearing rate of the installed system.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system ensuring that every coil tube product meets or exceeds international standards. The following certifications and compliance frameworks are maintained:
- ISO 9001:2015 — Quality Management System certification for manufacturing excellence and process control
- ISO 14001:2015 — Environmental Management System ensuring sustainable and responsible production practices
- ISO/TS 22163 — Quality management for rail applications (where applicable for industrial coil tube)
- CE Marking — Conformity with European Union directives for pressure equipment and construction products
- EN 10204 3.1 Certificate — Material test certificate issued by a qualified inspector confirming compliance with specified standards
- ASTM A269 / A270 Compliance — Standard specifications for welded and seamless austenitic stainless steel tubing
- GB/T 12771 — Chinese national standard for welded stainless steel tubes for general use
- NSF/ANSI 61 — Drinking water system components certification (for potable water applications)
- Third-Party Inspection: Independent verification by SGS, Bureau Veritas, or TÜV upon customer request
All production batches are accompanied by a full Mill Test Certificate (MTC) documenting chemical composition (C, Si, Mn, P, S, Cr, Ni, Mo), mechanical properties, and dimensional verification. The traceability system ensures that every coil can be traced back to its raw material mill certificate, providing complete supply chain transparency.
Unique Selling Points
- Exceptional Corrosion Resistance: The austenitic stainless steel construction provides a service life exceeding 50 years in aggressive aqueous environments, significantly outperforming carbon steel and copper alternatives in terms of total cost of ownership (TCO).
- High Precision Manufacturing: Tolerance-controlled cold drawing ensures uniform wall thickness and OD, critical for consistent heat transfer performance and seamless integration with finning and brazing processes.
- HVAC-Optimized Geometry: Coil dimensions are engineered specifically for fan coil and floor heating applications, maximizing the heating load bearing rate as validated by thermal performance literature.
- Hygienic Surface Quality: Electropolished and passivated surfaces inhibit biofilm growth and mineral scaling, ensuring long-term thermal efficiency without degradation.
- Full Traceability and Certification: Every product ships with comprehensive documentation meeting the most stringent international standards, facilitating compliance with building codes and industry regulations worldwide.