Stainless Steel Coil Tube (盘管) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Wenzhou Jixing Metal Materials Co., Ltd.), designed for thermal exchange applications within HVAC (Heating, Ventilation, and Air Conditioning) systems. This product is particularly suited for dry-condition fan coil units (FCU) and fresh air air-conditioning systems, where efficient heat transfer, corrosion resistance, and long-term structural integrity are paramount.
Coil tubes are formed by bending or coiling seamless or welded stainless steel tubes into predetermined spiral or serpentine geometries. The resulting configuration maximizes surface area within a compact envelope, enabling superior thermal exchange performance in evaporator coils, condenser coils, and heat exchanger assemblies.
2. Material & Properties
2.1 Base Material Grades
- SAE 304 / UNS S30400 — Austenitic stainless steel with excellent general corrosion resistance and formability; the most widely used grade for HVAC coil applications.
- SAE 316 / UNS S31600 — Molybdenum-enhanced austenitic stainless steel offering superior resistance to chloride-induced pitting and crevice corrosion; preferred for coastal or chemically aggressive environments.
- SAE 321 / UNS S32100 — Titanium-stabilized austenitic stainless steel with enhanced resistance to intergranular corrosion at elevated temperatures.
- SAE 316L / UNS S31603 — Low-carbon variant of S31600, suitable for welding applications requiring minimal sensitization risk.
2.2 Mechanical Properties (Typical Values for Annealed Condition)
| Property | SAE 304 | SAE 316 | SAE 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 520 | ≥ 520 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Density (kg/m³) | 8000 | 8030 | 8000 |
| Thermal Conductivity (W/m·K at 100°C) | 16.3 | 16.3 | 16.3 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 |
2.3 Chemical Composition (Wt%)
| Element | SAE 304 | SAE 316 | SAE 321 |
|---|---|---|---|
| Carbon (C) max | 0.08 | 0.08 | 0.08 |
| Chromium (Cr) | 18.0–20.0 | 16.0–18.0 | 17.0–19.0 |
| Nickel (Ni) | 8.0–10.5 | 10.0–14.0 | 9.0–13.0 |
| Molybdenum (Mo) | — | 2.0–3.0 | — |
| Titanium (Ti) | — | — | 5×C to 0.70 |
3. Specifications
3.1 Geometric Dimensions
| Parameter | Specification Range |
|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ12.7 mm (standard), custom up to Φ25.4 mm |
| Wall Thickness (WT) | 0.3 mm – 1.2 mm |
| Coil Length (per piece) | 1.0 m – 60.0 m |
| Coil Pitch (spiral spacing) | 5.0 mm – 50.0 mm (adjustable per design) |
| Number of Turns | 1 – 200+ (configurable) |
| End Preparation | Plain, flared, soldered, brazed, or threaded connections |
| Tolerance on OD | ±0.05 mm (per ASTM A733) |
| Tolerance on WT | ±10% of nominal |
3.2 Performance Parameters
| Parameter | Value / Description |
|---|---|
| Operating Pressure | Up to 2.5 MPa (365 psi) |
| Design Pressure | 3.0 MPa (435 psi) |
| Operating Temperature Range | −40°C to +120°C (standard); up to +200°C (special order) |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, CO₂ (R-744), ammonia (NH₃) |
| Water Flow Rate (typical) | 0.5 – 5.0 L/min per coil circuit |
| Heat Transfer Efficiency | U-value: 200 – 500 W/m²·K (dependent on geometry and fluid) |
| Expected Service Life | ≥ 20 years under standard HVAC operating conditions |
4. Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing workflow:
- Raw Material Selection & Inspection — Cold-rolled stainless steel strip or seamless tube billets are sourced from certified mills and subjected to spectroscopic composition analysis (OES — Optical Emission Spectroscopy) and ultrasonic testing (UT) for internal defects.
- Tube Forming / Seamless Drawing — Tubes are produced via cold-drawing (per ASTM A733) or seamless piercing methods, followed by cold finishing to achieve precise dimensional tolerances and surface finish (Ra ≤ 0.8 μm).
- Annealing & Pickling — Tubes undergo solution annealing at 1050–1150°C followed by controlled cooling to restore full austenitic structure and mechanical properties. Subsequent pickling and passivation remove scale and form a protective chromium oxide layer.
- Coil Bending / Forming — Precision CNC-controlled coil bending machines form tubes into the required spiral or serpentine geometry. Bend radius is maintained at a minimum of 2.5× OD to prevent wall thinning or ovality exceeding 5%.
- End Processing & Connection Fabrication — Tube ends are cut, deburred, and prepared with appropriate connection types (flaring, brazing sockets, threaded fittings, or expansion joints) per customer specifications.
- Quality Assurance & Testing — Each coil tube batch undergoes hydrostatic pressure testing (1.5× working pressure for 30 seconds), dimensional verification, and visual inspection for surface defects, weld integrity, and geometric accuracy.
5. Applications
5.1 Primary Application: Dry-Condition Fan Coil Systems
Stainless steel coil tubes serve as the core heat exchange elements in dry-condition fan coil units integrated with fresh air air-conditioning systems. In such configurations, the coil operates under dehumidification-free (dry) conditions, relying on sensible heat transfer to cool or heat the supply air. The corrosion-resistant properties of stainless steel ensure long-term performance stability even when exposed to ambient moisture, condensation, or chemically treated air streams.
5.2 Additional Applications
- Commercial HVAC Systems — Evaporator and condenser coils in rooftop units (RTU), air handling units (AHU), and split-type systems.
- Industrial Refrigeration — Heat exchangers in cold storage, process cooling, and cryogenic applications.
- Water Heating & Domestic Hot Water (DHW) — Immersion coils in water heaters and heat recovery systems.
- Food & Beverage Processing — Sanitary-grade heat exchangers requiring compliance with FDA and 3-A standards.
- Pharmaceutical & Laboratory Equipment — Clean-room air conditioning coils and precision temperature control systems.
- Marine & Coastal Applications — HVAC systems in vessels and coastal facilities where chloride corrosion resistance is critical.
6. Quality Certifications & Standards Compliance
| Standard / Certification | Scope of Applicability |
|---|---|
| ASTM A733 / A733M | Standard Specification for Stainless Steel Tubing, Seamless, for General Application |
| ASTM A269 / A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Service |
| ASME B31.5 | Pressure Piping — Refrigeration and Air-Conditioning |
| ISO 9001:2015 | Quality Management System Certification |
| EN 10217-7 | European Standard for Stainless Steel Tubes for Pressure Purposes |
| GB/T 14976 | Chinese National Standard for Seamless Stainless Steel Tubes for Fluid Transport |
| GB/T 12771 | Chinese National Standard for Welded Stainless Steel Tubes for Fluid Transport |
| CE Marking | Conformity with European Economic Area safety directives |
| MAT/EN 10204 3.1 | Material Test Certificate — Inspection Report |
7. Unique Selling Points
Exceptional Corrosion Resistance: Unlike traditional copper coil tubes, stainless steel coil tubes offer immunity to galvanic corrosion, ammonia attack, and chloride-induced degradation — extending service life by 3–5× in harsh environments.
Superior Cleanliness & Hygiene: The passive chromium oxide layer prevents microbial colonization and biofilm formation, making these coils ideal for food-grade, pharmaceutical, and clean-room applications.
Design Flexibility: Available in custom geometries, dimensions, and configurations to meet specific thermal performance requirements for dry-condition fan coil and fresh air system integration.
Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting circular economy principles and reducing lifecycle carbon footprint.
Low Lifecycle Cost: Despite higher initial material cost, the extended service life, reduced maintenance frequency, and resistance to fouling result in significantly lower total cost of ownership (TCO) compared to alternative materials.
8. Technical Notes on Dry-Condition Fan Coil Integration
In a dry-condition fan coil + fresh air air-conditioning system, the stainless steel coil tube operates exclusively for sensible heat transfer. The fresh air unit handles latent load (dehumidification), while the coil tube in the fan coil unit manages only the sensible cooling or heating load. This separation of functions offers several advantages when paired with stainless steel coil tubes:
- Elimination of condensate formation on coil surfaces, reducing microbial growth risk.
- Reduced maintenance intervals due to absence of moisture-related corrosion and fouling.
- Improved indoor air quality (IAQ) through independent humidity control in the fresh air pathway.
- Enhanced energy efficiency through optimized system zonal control and reduced fan energy consumption.
The stainless steel coil tube's thermal conductivity and corrosion resistance make it an optimal choice