Stainless Steel Coil Tube — Radiant Heating/Cooling & Fan Coil System Application Grade
Product Overview
The stainless steel coil tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed specifically for integration into radiant cooling/heating systems and fan coil unit (FCU) plus fresh air system (FAS) combined applications in modern building HVAC engineering. This product represents a specialized grade of seamless stainless steel coil tubing that meets the stringent thermal conductivity, corrosion resistance, and mechanical integrity requirements demanded by contemporary hydronic radiant and convective hybrid climate control systems.
Unlike conventional carbon steel or copper coil tubes, the stainless steel coil tube offers superior long-term durability in both potable water and non-potable hydronic loop applications, making it the preferred choice for high-end commercial, institutional, and residential buildings where system longevity, hygiene, and minimal maintenance are paramount design criteria.
Material & Properties
Base Material
- Primary Grade: Austenitic stainless steel — SUS304 / AISI 304 (UNS S30408) for standard applications; SUS316 / AISI 316 (UNS S31608) for enhanced chloride resistance in coastal or aggressive environments
- Compliance Standards: GB/T 12771, ASTM A269/A270, EN 10217-7, JIS G3459
Mechanical Properties
- Tensile Strength: ≥ 520 MPa (SUS304); ≥ 550 MPa (SUS316)
- Yield Strength: ≥ 205 MPa (SUS304); ≥ 240 MPa (SUS316)
- Elongation at Break: ≥ 40%
- Hardness: ≤ 92 HRB (annealed condition)
Thermal & Corrosion Performance
- Thermal Conductivity: 16.3 W/(m·K) at 25°C
- Corrosion Resistance: Excellent resistance to pitting, crevice, and intergranular corrosion in hydronic media; pitting resistance equivalent number (PREN) ≥ 19 (SUS316)
- Operating Temperature Range: −196°C to +450°C
- Chromium Content: 18–20% (SUS304); 16–18% (SUS316)
- Nickel Content: 8–10.5% (SUS304); 10–14% (SUS316)
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6 mm, Φ8 mm, Φ10 mm, Φ12 mm, Φ15 mm, Φ19 mm, Φ22 mm | GB/T 12771 |
| Wall Thickness | 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm | ASTM A269 |
| Coil Length per Roll | 50 m – 300 m (customizable) | — |
| Surface Finish | No. 1 (annealed & pickled), 2B, or Bright Annealed (BA) | ASTM A480 |
| Surface Roughness (Ra) | ≤ 0.8 μm (inner surface); ≤ 0.4 μm (BA finish) | — |
| Pressure Test | Hydrostatic test at 1.5× working pressure, hold ≥ 30 s | EN 10217-7 |
| Maximum Working Pressure | 1.6 MPa (standard); 2.5 MPa (high-pressure grade) | — |
| Bend Radius (Minimum) | ≥ 3× OD (without special tooling) | — |
| Dimensional Tolerance (OD) | ±0.1 mm (precision grade); ±0.3 mm (standard grade) | GB/T 12771 |
| Dimensional Tolerance (Wall) | ±10% (standard); ±5% (precision grade) | — |
| End Condition | Plain cut, or laser-cut with deburring | — |
| Packaging | Wooden crate or steel frame; moisture-proof wrapping | ISO 4180 |
Manufacturing Process
Process Flow
- Raw Material Selection: Virgin austenitic stainless steel wire rod or strip from certified mills (e.g., Outokumpu, POSCO, Taiyuan Stainless Steel), with full mill test certificates (MTC) per EN 10204 Type 3.1.
- Coiling & Straightening: Continuous coiling on precision mandrels with controlled tension to achieve uniform OD and wall thickness. Straightening performed via multi-roll or cold-drawing methods.
- Heat Treatment (Solution Annealing): Annealing at 1050–1100°C followed by rapid water quench to ensure full austenitic microstructure, eliminate work-hardening, and achieve maximum corrosion resistance. This step is critical for preventing intergranular sensitization.
- Pickling & Descaling: Removal of oxide scale via controlled acid immersion (HNO₃/HF blend) to achieve a clean, passive surface free of scale and contamination.
- Surface Finishing: Electropolishing or mechanical polishing for BA finish applications requiring low Ra values; passivation treatment with citric acid or nitric acid solution to restore chromium oxide passive layer.
- Quality Inspection: Dimensional verification (OD, wall thickness, straightness), hydrostatic pressure testing, spectroscopic chemical analysis (PMI), and visual/eddy-current flaw detection per ASTM E709.
- Coil Packing & Dispatch: Coils wound onto precision steel flanges, wrapped in PE film and kraft paper, and secured in export-grade wooden crates or steel frames.
Process Controls for Radiant/Fan Coil Applications
The manufacturing process incorporates additional controls specific to HVAC coil applications:
- Inner Surface Cleanliness: Critical for hydronic systems to prevent biofilm formation and ensure efficient heat transfer. Ra ≤ 0.8 μm ensures minimal fouling resistance.
- Uniformity of Wall Thickness: Essential for consistent heat exchange performance across the coil length and prevention of local stress concentration during brazing or welding.
- Non-Contamination Handling: All post-annealing handling performed with stainless steel tools only, preventing carbon steel contamination that could initiate corrosion.
Applications
Primary Application Domains
- Radiant Cooling & Heating Systems: Stainless steel coil tubes embedded in concrete slabs, ceiling panels, or wall assemblies for hydronic radiant temperature control. The coil configuration allows precise control of water flow and temperature distribution across large floor areas.
- Fan Coil Units (FCU): Integration into fan coil plus fresh air system (FAS) configurations where the coil tube serves as the heat exchange element for chilled water or hot water circulation, providing zone-level thermal comfort.
- Hybrid Radiant + Convective Systems: Combined application where radiant coils handle sensible heat loads while fan coil units manage latent loads and fresh air ventilation — a configuration particularly suited to large-span buildings with high ceiling heights.
- Underfloor Heating (UFH): Stainless steel coil tubes installed in screed layers for residential and commercial space heating, offering superior durability compared to PEX or copper alternatives in long-term service.
- Specialized HVAC Applications: Pharmaceutical cleanrooms, food processing facilities, hospitals, and laboratories where hygienic design and corrosion resistance are non-negotiable requirements.
Engineering Advantages in Combined Radiant + Fan Coil Systems
In the combined radiant cooling/heating and fan coil plus fresh air system architecture, the stainless steel coil tube provides the following engineering advantages:
- Eliminates the condensation risk inherent in conventional chilled beam and radiative ceiling systems when properly designed with stainless steel's thermal mass characteristics
- Provides a service life exceeding 50 years under normal hydronic conditions, significantly outperforming carbon steel alternatives (10–20 years) and copper tubes (25–35 years in aggressive water chemistry)
- Enables compact coil configurations with minimal bend radii, facilitating dense heat exchange surface packing in ceiling or floor assemblies
- Compatible with all major hydronic water treatment programs, including inhibitor-free systems
Quality Certifications & Compliance
Product Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing operations
- ISO 14001:2015 — Environmental Management System
- CE Marking — Conformity with European Construction Products Regulation (CPR) for building component applications
- Mill Test Certificate (MTC) — Provided per EN 10204 Type 3.1 for each batch, including chemical composition, mechanical properties, and heat treatment records
Material & Performance Standards
- GB/T 12771 — Seamless stainless steel tubes for fluid transport
- ASTM A269 / A270 — Specification for seamless and welded austenitic stainless steel tubing
- EN 10217-7 — Heat-resistant, creep-resistant and high-temperature mechanical properties austenitic stainless steel tubes
- JIS G3459 — Seamless and welded austenitic stainless steel tubes and bars
- NSF/ANSI 61 — Drinking water system components (for potable water applications)
- WRAS Approval — Water Regulations Advisory Scheme (UK market)
Testing & Inspection Protocol
- Chemical Analysis: X-ray fluorescence (XRF) spectroscopy for rapid alloy verification; wet chemical analysis for confirmatory testing
- Mechanical Testing: Tensile testing per ASTM A370; hardness testing per ASTM B557
- Pressure Testing: 100% hydrostatic testing at 1.5× specified working pressure with minimum 30-second hold time
- Dimensional Inspection: Automated optical measurement of OD, wall thickness, and straightness
- Non-Destructive Testing (NDT): Eddy current inspection per ASTM E709 for surface and near-surface defect detection; visual inspection per ASTM E94
- Corrosion Testing: Salt spray testing per ASTM B117 (≥ 500 hours, no pitting for SUS316 grade); intergranular corrosion testing per ASTM A262 Practice E
Unique Selling Points
1. Engineered for Combined HVAC System Integration
Unlike generic stainless steel tubing, this coil tube product is specifically designed and validated for use in combined radiant cooling/heating and fan coil plus fresh air system configurations. The dimensional tolerances, surface finish specifications, and mechanical properties are optimized for the unique thermal cycling, pressure fluctuations, and water quality conditions encountered in hybrid HVAC systems.
2. Extended Service Life with Zero Corrosion Maintenance
The full austenitic stainless steel construction provides a design service life exceeding 50 years, eliminating the need for corrosion monitoring, cathodic protection, or periodic replacement. This translates to significant lifecycle cost savings compared to carbon steel alternatives, particularly in applications where system access for maintenance is limited (e.g., embedded floor or ceiling coils).
3. Hygienic Surface for Sensitive Environments
The low surface roughness (Ra ≤ 0.8 μm inner surface) and passive chromium oxide layer prevent biofilm formation and bacterial colonization, making this product suitable for pharmaceutical, food processing, and healthcare applications where water quality and hygiene are critical compliance requirements.
4. Precision Manufacturing with Full Traceability
Each coil tube batch is manufactured under full quality traceability with mill test certificates, heat treatment records, and batch-specific chemical and mechanical test data. This ensures compliance with international project specifications and facilitates warranty claims and performance verification throughout the system lifecycle.
5. Environmental Sustainability
Stainless steel is 100% recyclable with no loss of material properties. The extended service life and elimination of replacement cycles result in significantly lower embodied carbon compared to shorter-lived alternatives. The manufacturing process incorporates closed-loop water treatment and energy recovery systems consistent with ISO 14001 environmental management requirements.
Technical Advisory Notes
Design Consideration: When specifying stainless steel coil tubes for radiant cooling applications, ensure that the minimum water supply temperature exceeds the dew point of the conditioned space by a minimum of 3°C to prevent condensation on the coil surface. The high thermal conductivity of stainless steel (16.3 W/m·K) means that surface temperatures closely track water temperatures, requiring careful psychrometric analysis during system design.
Water Quality Requirement: For optimal long-term performance, hydronic water quality should maintain: pH 6.5–8.5, dissolved oxygen ≤ 0.1 mg/L, total iron ≤ 10 mg/L, and chloride ≤ 200 mg/L (SUS304) or ≤ 1000 mg/L (SUS316). Regular water quality monitoring is recommended per ASHRAE Guideline 12.
Installation Note: Minimum bend radius of 3× OD should be maintained during field fabrication. All welds should be performed using matching stainless steel filler metal (e.g., ER308L for SUS304 base metal) with proper purge gas protection to maintain corrosion resistance at weld zones.