Stainless Steel Coil Tube for Low-Temperature Air Conditioning Heat Exchange Systems
Product Overview
The Stainless Steel Coil Tube (Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component specifically designed for low-temperature air distribution systems and cooling coil heat exchange applications. This product represents an advanced solution addressing the critical thermal efficiency challenges inherent in low-temperature air conditioning (Low-Temperature Air Conditioning, LTAC) systems, where enhanced heat transfer performance, corrosion resistance, and long-term operational reliability are paramount.
Unlike conventional carbon steel or copper coil tubes, the stainless steel coil tube leverages the superior metallurgical properties of austenitic stainless steel grades to deliver exceptional thermal conductivity, mechanical strength, and resistance to the aggressive environments encountered in HVAC (Heating, Ventilation, and Air Conditioning) and refrigeration systems. The coil tube geometry is optimized to maximize the heat transfer surface area while minimizing pressure drop, thereby improving the overall Coefficient of Performance (COP) of the cooling system.
Material & Properties
Base Material
- Primary Grade: Austenitic Stainless Steel — SUS304 (UNS S30400) / SUS316 (UNS S31600)
- Alternative Grades: SUS304L (UNS S30403) for enhanced weldability; SUS321 (UNS S32100) for high-temperature stability
- Alloy Composition (SUS304): Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤2.0%, Carbon (C) ≤0.08%, Silicon (Si) ≤1.0%, Phosphorus (P) ≤0.045%, Sulfur (S) ≤0.030%
- Alloy Composition (SUS316): Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%, Carbon (C) ≤0.08%
Physical and Mechanical Properties
- Density: 8.0 g/cm³ (7.9 g/cm³ for SUS304)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304); 14.6 W/(m·K) at 20°C (SUS316)
- Specific Heat Capacity: 500 J/(kg·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (10–100°C)
- Tensile Strength: ≥520 MPa (SUS304); ≥485 MPa (SUS316)
- Yield Strength: ≥205 MPa (0.2% offset)
- Hardness: ≤92 HRB (annealed condition)
- Operating Temperature Range: −196°C to +870°C (SUS304); −196°C to +870°C (SUS316)
Corrosion Resistance Characteristics
- Pitting Resistance Equivalent Number (PREN): 19–20 (SUS304); 24–26 (SUS316)
- Resistance to: Condensate corrosion, microbial-induced corrosion (MIC), chloride-induced pitting, acid condensate attack, and high-humidity environments
- Passivation: Self-healing chromium oxide passive film (Cr₂O₃) providing inherent corrosion protection
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.70 mm / 15.88 mm / 19.05 mm (1/4" to 3/4" imperial series) | ASTM A269 / GB/T 14976 |
| Wall Thickness (WT) | 0.50 mm – 2.00 mm (customizable) | ASTM A213 / GB/T 14975 |
| Coil Pitch (Center-to-Center) | 12.7 mm – 25.4 mm (0.5" – 1.0") | ISO 2198 / ASHRAE Standard 34 |
| Coil Diameter (Bundle) | 100 mm – 500 mm (configurable per application) | Manufacturer Specification |
| Tube Length (Per Coil) | 0.5 m – 6.0 m (standard); up to 12.0 m (custom) | — |
| Surface Finish | BA (Bright Annealed) / No. 4 Brushed / Mirror (Ra ≤ 0.4 μm) | ASTM A403 / GB/T 4237 |
| End Treatment | Plain end / Flanged / Threaded (G, NPT, BSP) / Brazed / Welded | ASME B1.20.1 / ISO 7 |
| Fin Configuration (if finned) | Integral lamination fins / Slip-on aluminum fins; Fin density: 8–16 fins/inch | ASHRAE Standard 34 |
| Pressure Rating | Up to 1.6 MPa (PN16) standard; up to 4.0 MPa (PN40) custom | ASME B31.9 / GB/T 12771 |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, R-22, R-513A, CO₂ (R-7444) | ASHRAE Standard 34 / EN 378 |
| Tolerance (OD) | ±0.05 mm (precision grade); ±0.10 mm (standard grade) | ASTM A269 / GB/T 14976 |
| Delivery Form | Coiled tube (coil tube) / Straight tube / Pre-formed coil bundle | — |
Manufacturing Process
Step 1: Raw Material Procurement and Inspection
High-purity stainless steel billets or hot-rolled strips are sourced from certified mills meeting ASTM A276 or GB/T 4237 standards. Incoming material undergoes spectroscopic analysis (Optical Emission Spectroscopy, OES) to verify chemical composition, along with mechanical testing including tensile, hardness, and impact tests.
Step 2: Cold Drawing / Seamless Piping Production
Seamless stainless steel tubes are produced via the Mannesmann piercing process or the cross-rolling method, followed by cold drawing to achieve precise dimensional tolerances. Cold drawing enhances grain structure alignment, improves surface finish, and increases mechanical properties by work hardening. The drawing process typically achieves a reduction ratio of 30–60% in cross-sectional area.
Step 3: Heat Treatment (Solution Annealing and Pickling)
Tubes are subjected to solution annealing at 1050–1100°C in a protective atmosphere (argon or hydrogen) to relieve cold-work stresses, restore full austenitic microstructure, and optimize corrosion resistance. Subsequent acid pickling (HNO₃/HF mixture) removes scale and oxide layers, followed by water quenching and passivation treatment to establish a uniform chromium oxide passive film.
Step 4: Coil Forming
Straight tubes are fed through a precision coil forming machine equipped with adjustable mandrels and guide rollers. The forming process utilizes progressive bending stations to achieve the target coil pitch and diameter without inducing plastic deformation, cracking, or ovality. The coil forming parameters are controlled to maintain:
- Ovality ≤ 1.5% of OD
- Wall thickness reduction ≤ 5%
- Residual stress within acceptable limits
Step 5: Finning (Optional)
For enhanced heat transfer performance, integral lamination fins are formed using a rolling finning machine that compresses the tube wall outward to create uniform fins. Alternatively, aluminum slip-on fins are mechanically attached to the tube OD. Fin thickness, density, and pattern are optimized based on the specific application's heat transfer requirements.
Step 6: End Processing and Assembly
Tube ends are machined for flanging, threading, or brazing/welding preparation. Coil bundles are assembled with headers, expansion joints, and mounting brackets as specified by the system design. Brazing is performed using phosphorus-copper (Cu-P) brazing filler metals in a vacuum or inert gas atmosphere to prevent oxidation.
Step 7: Quality Inspection and Testing
- Dimensional Inspection: Coordinate Measuring Machine (CMM) verification of OD, wall thickness, coil pitch, and straightness
- Non-Destructive Testing (NDT): Eddy current testing (ECT) for wall thickness and defect detection; dye penetrant testing (PT) for surface cracks; ultrasonic testing (UT) for internal defects
- Pressure Testing: Hydrostatic pressure test at 1.5× working pressure for a minimum of 30 seconds; pneumatic testing as an alternative
- Corrosion Testing: Salt spray testing (ASTM B117) for minimum 1000 hours; intergranular corrosion testing (ASTM A262 Practice E)
- Heat Transfer Performance Testing: Validation of heat transfer coefficient (U-value) and pressure drop (ΔP) under rated conditions
Applications
Primary Applications
- Low-Temperature Air Distribution Systems: Cooling coils in chilled air systems operating at supply air temperatures of 10–16°C, where anti-condensation and high-efficiency heat exchange are critical
- Commercial and Industrial HVAC: Air handling units (AHUs), rooftop units (RTUs), fan coil units (FCUs), and chiller evaporators/condensers
- Refrigeration Systems: Evaporator and condenser coils in medium and low-temperature refrigeration equipment
- Clean Room and Pharmaceutical Applications: Precision temperature control systems requiring hygienic, corrosion-resistant heat exchange components
- Food Processing and Cold Storage: Refrigerated display cases, cold chain logistics, and food processing plant cooling systems
- Marine and Offshore Applications: HVAC and refrigeration systems in vessels and offshore platforms exposed to saltwater environments
- Data Center Cooling: High-density cooling coils for server room temperature management
- Automotive and Transportation: HVAC evaporator coils and heat exchange components in vehicles
System Integration Context
In low-temperature air conditioning systems, the coil tube serves as the primary heat exchange element where refrigerant absorbs thermal energy from the air stream. The optimization of coil tube geometry — including tube diameter, wall thickness, coil pitch, fin density, and tube layout pattern (e.g., staggered vs. in-line arrangement) — directly influences the system's overall energy efficiency. Research in heat transfer performance optimization has demonstrated that stainless steel coil tubes with optimized geometries can achieve heat transfer coefficients (U-values) of 150–350 W/(m²·K) for air-to-refrigerant heat exchange, with pressure drops reduced by 15–30% compared to conventional designs.
Quality Certifications and Standards Compliance
International Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European Union directives (Machinery Directive 2006/42/EC, Pressure Equipment Directive 2014/68/EU)
- EN 10204 3.1 — Inspection certificate for material conformity
- EN 10204 3.2 — Inspection certificate with full product testing documentation
Material and Product Standards
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and General Applications
- ASTM A213 — Standard Specification for Seamless Austenitic Chromium-Chromium-Nickel Stainless Steel Tubing for Heat-Transfer and Reformer Applications
- ASTM A403 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe
- GB/T 14976 — Seamless Stainless Steel Tubes for Fluid Transport (Chinese National Standard)
- GB/T 14975 — Welded Stainless Steel Tubes for Fluid Transport (Chinese National Standard)
- GB/T 4237 — Stainless Steel Plates, Sheets, and Strips (Chinese National Standard)
- JIS G3446 — Stainless Steel Tubes for General Purposes (Japanese Industrial Standard)
- EN 10216-5 — Non-ferrous metal tubes — Technical delivery conditions — Part 5: Austenitic stainless steel tubes
Performance and Safety Standards
- ASHRAE Standard 34 — Safety and Environmental Standard for Refrigeration Systems
- ASHRAE Standard 15 — Safety Standard for Refrigeration Systems
- EN 378 — Safety and Environmental Requirements for Refrigeration Systems
- ASME B31.9 — Pressure Piping, Refrigeration Piping and Heat Transfer Components
- GB/T 17758 — Safety and Environmental Requirements for Refrigerating Systems (Chinese National Standard)
Unique Selling Points
- Exceptional Corrosion Resistance: The austenitic stainless steel construction provides outstanding resistance to condensate corrosion, chloride-induced pitting, and microbial-induced corrosion (MIC), significantly extending service life compared to copper or carbon steel alternatives — particularly in humid, high-chloride, or aggressive chemical environments.
- Optimized Heat Transfer Performance: Precision-engineered coil geometry with optimized tube pitch, diameter, and fin