Stainless Steel Coil Tube (Coiltube) for HVAC Systems — Anti-Freeze Engineering Grade
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered heat exchange component designed specifically for air conditioning units (ACUs) and HVAC (Heating, Ventilation, and Air Conditioning) systems. This product represents a critical interface between refrigerant circulation loops and ambient air, enabling efficient thermal transfer under a wide range of operating conditions. The coil tube is engineered with specialized anti-freeze protection measures to ensure reliable performance in environments subject to sub-zero ambient temperatures, eliminating the risk of ice formation, tube rupture, and system damage that commonly plague conventional coil assemblies.
This product is categorized under industrial literature and technical documentation (Reference No. 848), reflecting its role as a benchmark component in the stainless steel tube industry for HVAC applications requiring enhanced freeze-resistance and long-term durability.
Material & Properties
Base Material Composition
- Primary Alloy: Austenitic stainless steel conforming to ASTM A213 / ASME SA-213 specifications
- Grade Options: 304 (UNS S30400), 316 (UNS S31600), 316L (UNS S31603)
- Chemical Composition (316L Grade):
- Chromium (Cr): 16.0% – 18.0%
- Nickel (Ni): 10.0% – 14.0%
- Molybdenum (Mo): 2.0% – 3.0%
- Carbon (C): ≤ 0.030%
- Maximum Sulfur (S): ≤ 0.030%
- Iron (Fe): Balance
Mechanical Properties
- Tensile Strength: ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
- Elongation: ≥ 40% (50 mm gauge length)
- Hardness: ≤ 217 HB (Brinell)
- Operating Temperature Range: −196°C to +870°C (−320°F to +1,600°F)
Thermal Properties
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Thermal Conductivity (at 100°C): 22.1 W/(m·K)
- Specific Heat Capacity: 0.50 J/(g·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
Corrosion Resistance
- Excellent resistance to atmospheric corrosion, deionized water, and mild alkaline solutions
- Superior pitting and crevice corrosion resistance due to molybdenum content (316L grade)
- Immune to intergranular corrosion following solution annealing treatment
- Resistant to condensation corrosion from humid air streams in HVAC environments
Anti-Freeze Performance Characteristics
- Maintains ductility and structural integrity at temperatures as low as −196°C
- No embrittlement transition observed within the operating temperature envelope
- Resistant to freeze-thaw cycle fatigue (validated for ≥ 10,000 cycles)
- Compatible with glycol-based anti-freeze fluids (ethylene glycol, propylene glycol) without material degradation
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Reference No. | 848 | Wenzhou Jixing Metal Materials Co., Ltd. |
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4") | ASTM A213 |
| Wall Thickness | 0.50 mm – 1.65 mm | ASME SA-213 |
| Coil Pitch | 12 mm – 35 mm (adjustable per application) | Custom engineering |
| Coil Diameter | 50 mm – 300 mm | Custom engineering |
| Tube Length (Straight Section) | Custom up to 6,000 mm | — |
| Surface Finish | 2B Annealed / Polished (Ra ≤ 0.4 μm available) | ASTM A478 |
| End Condition | Plain, Flared, Grooved, or Brazed Fitting | Customer specification |
| Operating Pressure (Design) | Up to 2.5 MPa (363 psi) | ASME BPV Code Section VIII |
| Refrigerant Compatibility | R-134a, R-410A, R-32, R-290, Glycol Solutions | ASHRAE Standard 34 |
| Anti-Freeze Rating | Functional down to −40°C (−40°F) | Internal test protocol |
| Welding Compatibility | TIG (GTAW), MIG (GMAW), Brazing (silver-based) | ASME SA-213 Appendix |
| Packaging | Coiled on protective spools; moisture-barrier wrapping | ISO 4126 |
Manufacturing Process
Stage 1: Raw Material Selection and Incoming Inspection
High-purity austenitic stainless steel strip or seamless tube stock is sourced from certified mills. Each batch undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with the specified grade. Mechanical property verification is performed on representative samples prior to processing.
Stage 2: Cold Drawing and Precision Forming
Seamless tube stock is cold-drawn through calibrated dies to achieve the required outer diameter and wall thickness with dimensional tolerances of ±0.05 mm. This cold-working process enhances mechanical strength while maintaining the austenitic microstructure integrity essential for cryogenic performance.
Stage 3: Solution Annealing
The formed tube is subjected to solution annealing at 1,050°C – 1,100°C followed by controlled water quenching. This process:
- Relieves residual stresses introduced during cold forming
- Homogenizes the microstructure
- Prevents chromium carbide precipitation at grain boundaries
- Restores full ductility and corrosion resistance
Stage 4: Coil Forming (Coiling)
The annealed tube is coiled using precision CNC-controlled forming equipment. The coiling process maintains a consistent pitch and coil diameter, critical for uniform heat transfer performance in HVAC coil assemblies. Forming parameters are optimized to prevent work hardening and micro-cracking at bend radii.
Stage 5: Surface Treatment and Cleaning
Finished coil tubes undergo:
- Acid pickling to remove oxide scale
- Passivation treatment (citric acid or nitric acid-based) to restore the passive chromium oxide film
- Ultrasonic cleaning to remove internal contaminants
- Optional polishing to achieve Ra ≤ 0.4 μm surface finish for enhanced heat transfer efficiency
Stage 6: Anti-Freeze Performance Validation
Each production batch undergoes rigorous anti-freeze testing protocols:
- Cryogenic Impact Testing: Charpy V-notch impact testing at −40°C to verify toughness retention
- Freeze-Thaw Cycle Testing: 100 cycles of immersion in water (20°C) → freezing (−20°C) → thawing to validate structural integrity
- Pressure Testing: Hydrostatic proof pressure test at 1.5× design pressure for 30 minutes with no leakage or permanent deformation
- Refrigerant Compatibility Testing: Exposure to glycol-based anti-freeze solutions for 500 hours with post-exposure mechanical and corrosion evaluation
Stage 7: Final Inspection and Traceability
Each coil tube assembly receives a unique traceability code linked to material certificates, heat numbers, and test reports. Non-Destructive Testing (NDT) including eddy current inspection and dye penetrant testing ensures freedom from surface and near-surface defects.
Applications
Primary Application: Air Conditioning Unit (ACU) Evaporator/Condenser Coils
The stainless steel coil tube serves as the core heat exchange element in commercial and industrial air conditioning units. Its anti-freeze design makes it particularly suited for:
- Low-Ambient HVAC Systems: Units operating in climates with winter temperatures below −10°C, where conventional copper coil tubes risk freeze-induced rupture
- Outdoor Unit Heat Exchangers: Condenser coils exposed to freezing rain, snow accumulation, and rapid temperature fluctuations
- Commercial Refrigeration: Evaporator coils in walk-in coolers, blast freezers, and cold storage facilities
- Industrial Process Cooling: Chilled water coil circuits in manufacturing plants requiring continuous operation without seasonal shutdown
- Data Center Cooling: Precision air conditioning systems requiring 24/7 reliability with glycol-based anti-freeze loops
- Automotive and Marine HVAC: Compact coil assemblies for vehicles and vessels operating in polar or sub-polar environments
- Pharmaceutical and Food Processing: Sanitary-grade coil assemblies where corrosion resistance and cleanability are paramount
Anti-Freeze Technical Measures — System Integration
The coil tube is designed to be integrated with comprehensive anti-freeze protection systems including: low-temperature cutoff switches, glycol-based heat transfer fluid circuits, defrost cycle controllers, and thermal insulation blankets. The stainless steel material's inherent resistance to freeze-thaw degradation ensures that even in the event of partial freezing, the tube maintains structural integrity and can be safely thawed without permanent damage.
Quality Certifications
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
- ASME SA-213 — Material specification compliance for austenitic chromium-nickel steel tubing
- ASTM A213 / A269 — Standard specifications for seamless austenitic stainless steel tubing
- TÜV Rheinland — Third-party product certification for HVAC components
- SGS — Independent material testing and chemical composition verification
- RoHS 2011/65/EU — Restriction of Hazardous Substances compliance
- REACH Regulation (EC) No 1907/2006 — Chemical safety compliance
Unique Selling Points
- Superior Cryogenic Performance: Maintains full mechanical properties down to −196°C, eliminating the brittle fracture risk associated with copper and aluminum coil tubes in freezing environments
- Extended Service Life: Stainless steel coil tubes demonstrate 3–5× the service life of copper alternatives in corrosive HVAC environments, reducing lifecycle replacement costs
- Anti-Freeze Engineering Heritage: Developed with specific reference to air conditioning unit anti-freeze technical measures, incorporating lessons learned from field failures and best practices in freeze protection engineering
- Full Traceability: Every coil tube is traceable to mill heat number, with complete documentation of material certificates, test results, and manufacturing parameters
- Customization Capability: Flexible manufacturing parameters allow tailoring of coil pitch, diameter, tube dimensions, and end conditions to specific HVAC system requirements
- Regulatory Compliance: Certified against international standards ensuring acceptance in global HVAC markets without additional testing or re-certification
Technical Documentation Reference
This product specification is derived from and aligned with the technical learning material: "Anti-Freeze Technical Measures for Air Conditioning Unit Coil Tubes" (《空调机组盘管防冻技术措施》), Reference No. 848, developed under the literature study and technical knowledge transfer program of Wenzhou Jixing Metal Materials Co., Ltd. The engineering parameters, anti-freeze performance data, and application guidelines presented herein reflect validated technical practices for coil tube design, material selection, and system integration in HVAC applications subject to freezing conditions.