Stainless Steel Coil Tube (盘管 / Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for hydronic heating, cooling, and ventilation (HVAC) applications. Unlike conventional straight-length stainless steel pipes, coil tubes are delivered in continuous spiral or helical configurations, enabling efficient integration into fan coil units (FCUs), air handling units (AHUs), and radiant heating/cooling systems. The product is particularly suited for high-performance thermal exchange applications in commercial buildings, underground transit systems (such as metro/subway public areas), hospitals, and data centers where reliable heat transfer and long-term corrosion resistance are critical.
Coiltubes are fabricated by cold-forming stainless steel strip into seamless tubular sections and then coiling the finished tube into standardized or custom-length spirals. This manufacturing approach eliminates the need for longitudinal welds, resulting in superior mechanical integrity and enhanced resistance to internal corrosion and fouling.
2. Material & Properties
2.1 Material Grades
- AISI 304 / UNS S30408 — General-purpose austenitic stainless steel offering excellent corrosion resistance in atmospheric and mildly corrosive environments. The most commonly specified grade for HVAC coil tube applications.
- AISI 316 / UNS S31603 — Molybdenum-enhanced austenitic stainless steel providing superior resistance to chlorides, acidic condensates, and marine atmospheres. Recommended for subway tunnel environments where chloride ion exposure may occur.
- AISI 316L / UNS S31603L — Low-carbon variant of 316L suitable for applications requiring welding or exposure to elevated temperatures.
2.2 Key Mechanical and Physical Properties
| Property | AISI 304 | AISI 316 | Test Standard |
|---|---|---|---|
| Tensile Strength (Ultimate) | ≥ 515 MPa | ≥ 515 MPa | ASTM A270 / EN 10216-5 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ≥ 205 MPa | ASTM A270 |
| Elongation (in 50 mm gauge length) | ≥ 40% | ≥ 40% | ASTM A270 |
| Hardness (Rockwell B) | ≤ 95 HRB | ≤ 95 HRB | ASTM A270 |
| Thermal Conductivity (at 20 °C) | 16.3 W/(m·K) | 16.3 W/(m·K) | — |
| Specific Heat Capacity (at 20 °C) | 500 J/(kg·K) | 500 J/(kg·K) | — |
| Corrosion Potential (in potable water) | Passive | Passive | ASTM G48 |
| Pitting Resistance (PREN value) | ≈ 19 | ≈ 25 | ISO 15653 |
2.3 Surface Finish
- Bright Annealed (BA) / No. 1 Finish — Smooth, reflective surface ideal for hygienic and high-efficiency heat exchange applications.
- 2B Finish — Mill-finished with a matte appearance suitable for general-purpose HVAC systems.
- Electro-polished Finish — Available upon request for applications requiring minimal surface roughness (< 0.5 μm Ra) to reduce biofilm formation.
3. Specifications
| Parameter | Specification / Range | Applicable Standard |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (typical); up to 38.1 mm on request | ASTM A270 / EN 10216-5 |
| Wall Thickness (WT) | 0.4 mm – 1.2 mm | ASTM A270 |
| Coil Inner Diameter (Coil ID) | 150 mm – 600 mm (configurable) | Manufacturer standard |
| Tube Length per Coil | 3 m – 50 m per continuous coil (custom lengths available) | — |
| Coil Height (Stack Height) | 50 mm – 200 mm | — |
| Seam Type | Seamless (cold-formed) — no longitudinal weld | ASTM A270 |
| End Forming | Plain, threaded (BSPP/BSPT/NPT), flanged, or grooved | ISO 7 / ASME B1.20.1 |
| Operating Temperature Range | −196 °C to +870 °C (AISI 304); −196 °C to +870 °C (AISI 316) | ASME BPV Code |
| Maximum Operating Pressure | Up to 10.0 MPa (dependent on OD, WT, and grade) | ASME B31.9 |
| Tolerance on OD | ± 0.10 mm | EN 10216-5 |
| Tolerance on Wall Thickness | ± 10% of nominal | EN 10216-5 |
| Roundness Tolerance | ≤ 10% of wall thickness | EN 10216-5 |
| Material Certificate | EN 10204 Type 3.1 / ASTM A923 Type 1 | — |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous, multi-stage manufacturing sequence designed to ensure dimensional accuracy, mechanical consistency, and surface integrity:
- Raw Material Selection — Cold-rolled stainless steel strip (coils) of certified grade (AISI 304/316/316L) is procured from accredited mills. Incoming material is inspected for chemical composition (via Optical Emission Spectrometry, OES), mechanical properties, and surface quality.
- Strip Annealing and Pickling — Cold-rolled strip undergoes solution annealing at 1050–1150 °C followed by acid pickling (HNO₃/HF blend) to restore full austenitic microstructure, remove oxide scale, and achieve the specified surface finish.
- Forming (Cold Roll Forming) — The strip is fed through a series of precision roller stations (typically 8–12 passes) that progressively form the flat strip into a seamless tube. This process maintains grain structure integrity and avoids the metallurgical weaknesses associated with welded seams.
- Coiling — The formed seamless tube is wound onto a mandrel to create the spiral coil geometry. Coiling parameters (tension, speed, mandrel diameter) are precisely controlled to prevent tube deformation, kinking, or residual stress accumulation.
- Post-Coiling Annealing (Optional) — For applications requiring full stress relief, the coiled tube may undergo a controlled annealing cycle at 850–950 °C in a protective atmosphere (H₂/N₂) to eliminate cold-work hardening effects and restore maximum ductility.
- End Processing — Coil ends are trimmed, deburred, and optionally formed into threads, grooves, or flanges per customer specification.
- Quality Inspection — Each coil undergoes dimensional verification (OD, WT, coil diameter via laser gauge), hydrostatic pressure testing (at 1.5× working pressure), visual inspection, and optional eddy current or ultrasonic testing for internal defect detection.
- Packaging and Dispatch — Finished coils are wrapped in moisture-proof protective film, secured with steel strapping, and palletized for safe transport.
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCUs) in Commercial HVAC Systems — Stainless steel coil tubes serve as the heat exchange medium in FCUs installed in offices, retail spaces, and institutional buildings. Their corrosion resistance ensures long service life even in humid environments.
- Metro / Subway Public Area Ventilation Systems — As demonstrated in the study "Calculation Analysis of Fresh Air + Fan Coil Tube System Adopted in Subway Public Areas", coil tubes are integral to hybrid ventilation systems that combine fresh air supply with fan coil units to maintain thermal comfort in underground transit stations. The sealed, seamless construction prevents leakage and condensate contamination in confined tunnel environments.
- Air Handling Units (AHUs) — Used in evaporator and condenser sections of rooftop and packaged AHUs for industrial and commercial facilities.
- Radiant Floor Heating and Cooling Systems — Coil tubes are embedded in floor slabs for hydronic radiant systems, where their thermal conductivity and corrosion resistance provide decades of reliable operation.
- Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) — Employed in counterflow and crossflow heat exchanger cores for energy-efficient ventilation.
5.2 Specialized Applications
- Pharmaceutical and food processing cleanroom HVAC systems (electro-polished finish)
- Marine and coastal facility HVAC (AISI 316/316L grade)
- Industrial process cooling and heating circuits
- Chiller and boiler circulation loops
6. Quality Certifications and Standards Compliance
| Standard / Certification | Description | Relevance |
|---|---|---|
| ASTM A270 | Standard Specification for Seamless and Wrought Steel Tubing, Austenitic Chromium-Chromium-Nickel Alloy Steel | Material and dimensional conformance |
| EN 10216-5 | Non-ferrous metal tubes and their accessories — Technical delivery conditions — Part 5: Nickel alloys and nickel alloy steels | European dimensional and mechanical requirements |
| ISO 9001:2015 | Quality Management Systems — Requirements | Manufacturing process quality assurance |
| EN 10204 Type 3.1 | Inspection Documents — Type and Content of Inspection Documents | Material certification and traceability |
| ASME B31.9 | Code for Pressure Piping — Building Services Piping | HVAC piping system design validation |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects | Safe for potable water contact (where applicable) |
| CE Marking | European Conformity | Market access for EU-regulated applications |
7. Unique Selling Points
- Seamless Construction — Cold-formed manufacturing eliminates longitudinal weld seams, providing uniform wall strength, superior pressure integrity, and reduced internal fouling compared to welded alternatives.
- Continuous Coil Delivery — Delivered as a continuous spiral coil, reducing field assembly labor, minimizing connection points, and lowering the risk of leak points in HVAC systems.
- Exceptional Corrosion Resistance — Austenitic stainless steel grades (304/316/316L) offer outstanding resistance to condensate corrosion, chloride-induced pitting, and general atmospheric degradation — critical for subway and coastal applications.
- Hygienic Surface Integrity — Available in electro-polished finish with Ra < 0.5 μm, minimizing biofilm adhesion and supporting stringent hygiene requirements in pharmaceutical and food-grade facilities.
- Thermal Performance — High thermal conductivity combined with seamless internal geometry ensures maximum heat transfer efficiency with minimal pressure drop across the coil circuit.
- Customization Capability — Wenzhou Jixing Metal Materials Co., Ltd. offers tailored OD, wall thickness, coil dimensions, and end-forming configurations to meet project-specific engineering requirements.
- Full Traceability — Every coil is accompanied by mill test certificates (MTC) providing complete chemical composition and mechanical property data, ensuring full material traceability per EN 10204 Type 3.1.
Reference Context: The performance characteristics of stainless steel coil tubes are validated in the technical study "Calculation Analysis of Fresh Air + Fan Coil Tube System Adopted in Subway Public Areas" (《地铁公共区采用新风+风机盘管系统的计算分析》), which demonstrates the effectiveness of hybrid fresh-air-plus-FCU systems in maintaining thermal comfort and air quality in underground metro public areas. The coil tube's thermal efficiency and corrosion resistance directly contribute to the system's long-term operational reliability in demanding transit environments.