Stainless Steel Evaporator Coil Tube — Refrigeration Circuit Series (Wenzhou Jixing)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Category: Precision Formed Tubing — Coil Tube / Evaporator Coil
Reference Standard: GB/T 14976, ASTM A269, EN 10217
Application Domain: Refrigeration & Air Conditioning (HVAC) Evaporator Systems
1. Product Overview
The Stainless Steel Evaporator Coil Tube is a precision-engineered spiral-wound tube designed specifically for integration into refrigeration circuit evaporators. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product serves as the core heat-exchange element in closed-loop refrigeration systems, where the refrigerant undergoes phase transition from liquid to vapor, absorbing thermal energy from the surrounding medium.
Unlike conventional copper evaporator coils, the stainless steel variant offers superior corrosion resistance, extended operational lifespan, and enhanced mechanical integrity under cyclic thermal loading. The coil geometry maximizes surface-area-to-volume ratio, thereby optimizing the heat transfer coefficient while maintaining compact system dimensions. Extensive experimental research has demonstrated that properly designed stainless steel evaporator coils achieve competitive heat exchange efficiency and dehumidification performance, rivaling traditional materials in controlled laboratory conditions.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards. The primary grades offered include:
- Grade 304 (UNS S30408): General-purpose refrigeration applications with moderate corrosion exposure.
- Grade 316 (UNS S31608): Enhanced resistance to chloride-induced pitting, suitable for coastal or chemically aggressive environments.
- Grade 321 (UNS S32103): Titanium-stabilized grade for applications involving elevated temperatures and thermal cycling.
2.2 Mechanical Properties (Typical Values — Annealed Condition)
| Property | Grade 304 | Grade 316 | Grade 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (A₅₀, %) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HBW) | ≤ 187 | ≤ 187 | ≤ 187 |
| Density (kg/m³) | 7,930 | 8,000 | 8,000 |
| Thermal Conductivity (W/m·K, at 100°C) | 16.3 | 14.6 | 16.3 |
| Coefficient of Thermal Expansion (10⁻⁶/K, 20–100°C) | 17.3 | 17.5 | 17.3 |
2.3 Corrosion Resistance Characteristics
The chromium oxide passive film (Cr₂O₃) formed on the stainless steel surface provides exceptional resistance against:
- Atmospheric corrosion in humid environments
- Condensate-induced pitting from dissolved chlorides
- Microbiologically induced corrosion (MIC)
- Galvanic corrosion when paired with dissimilar metals (mitigated through proper insulation)
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.0 mm – 12.0 mm (customizable) |
| Wall Thickness (WT) | 0.3 mm – 1.0 mm |
| Coil Pitch (Spiral Spacing) | 8 mm – 25 mm (adjustable per design) |
| Coil Outer Diameter | 50 mm – 300 mm |
| Tube Length (Uncoiled) | 1.0 m – 6.0 m (standard); up to 12.0 m (special order) |
| End Forming | Plain end, flared end, or brazed fitting compatible |
| Surface Finish | 2B (cold-rolled), BA (bright annealed), or polished (Ra ≤ 0.4 μm) |
| Pressure Rating (Hydrostatic Test) | 2.0 × Working Pressure, minimum 4.0 MPa |
| Operating Temperature Range | −196 °C to +450 °C |
| Refrigerant Compatibility | R-134a, R-410A, R-32, R-290, R-1234yf, ammonia (NH₃) |
| Dimensional Tolerance | OD: ±0.05 mm; WT: ±0.02 mm; Pitch: ±0.5 mm |
| Coil Turn Count | 5 – 200 turns (depending on coil diameter and pitch) |
| Packaging | Anti-static film wrapped, wooden crate or export carton |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel wire rod or seamless tube undergoes spectroscopic analysis (OES) to verify chemical composition compliance with ASTM/EN specifications. Certificates of Analysis (CoA) are reviewed for each heat lot.
- Coil Winding (Spiral Forming): Precision computer-controlled winding machines form the straight tube into a helical coil geometry. Tension control systems ensure uniform pitch and consistent wall thickness throughout the coil. Cold forming work-hardens the material, increasing yield strength by 15–25%.
- Heat Treatment (Annealing): Optional solution annealing at 1,050–1,150 °C followed by controlled cooling restores full ductility and eliminates residual stresses introduced during forming. This step is critical for maintaining corrosion resistance in the final product.
- Surface Finishing: Pickling and passivation treatments remove scale and contaminants, establishing the protective chromium oxide passive layer. Bright annealing in a reducing atmosphere (endothermic gas) produces a clean, oxide-free surface suitable for high-efficiency heat transfer.
- End Processing: Tube ends are cut to precise length using laser or mechanical saws, followed by deburring, chamfering, and optional flaring or crimping for brazed joint compatibility.
- Quality Inspection: Each coil undergoes hydrostatic pressure testing, dimensional verification using coordinate measuring machines (CMM), and visual surface inspection. Eddy current testing (ECT) screens for internal and external defects.
- Refrigerant Compatibility Testing: Sample coils are subjected to refrigerant cycling tests simulating operational conditions to validate long-term integrity and performance.
4.2 Key Process Parameters
| Process Step | Temperature (°C) | Duration | Cooling Method |
|---|---|---|---|
| Solution Annealing | 1,050 – 1,150 | 30 – 60 min | Furnace cool / air cool |
| Pickling | 60 – 80 | 15 – 30 min | Water rinse |
| Passivation | 20 – 25 (ambient) | 10 – 20 min | Deionized water rinse |
5. Applications
5.1 Primary Application Domains
- Commercial Refrigeration: Evaporator coils in walk-in coolers, display cases, and cold storage units where hygiene and corrosion resistance are paramount.
- Industrial HVAC Systems: Chilled water evaporators and air handling unit coils requiring resistance to condensate corrosion and chemical exposure.
- Food Processing Equipment: Heat exchangers in dairy, beverage, and pharmaceutical processing lines subject to frequent CIP (Clean-in-Place) cycles with aggressive cleaning agents.
- Marine & Offshore Refrigeration: Evaporator assemblies exposed to salt spray and high-humidity marine atmospheres.
- Cryogenic Applications: Low-temperature evaporators operating with R-23, R-508B, or liquid nitrogen where austenitic stainless steel maintains ductility at cryogenic temperatures.
- Automotive Refrigeration: Compact evaporator coils for electric vehicle battery thermal management systems.
5.2 Performance Advantages Over Conventional Materials
Experimental studies on evaporator coil heat exchange and dehumidification characteristics have confirmed that stainless steel coils achieve heat transfer coefficients within 85–95% of copper equivalents, while offering 5–10× longer service life in corrosive environments. The dehumidification effectiveness ratio (EER) remains stable over extended operational cycles without degradation from oxidation or scale formation.
6. Quality Certifications & Standards Compliance
| Standard / Certification | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System compliance |
| ASTM A269/A269M | Standard specification for seamless austenitic stainless steel tube |
| EN 10217-7 | European standard for stainless steel tubes for heat exchangers |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for heat exchangers |
| ASME BPV Section I | Boiler and Pressure Vessel Code compliance (where applicable) |
| NSF/ANSI 61 | Drinking water system components — health effects (food-grade applications) |
| CE Marking | European conformity for machinery and pressure equipment directives |
| RoHS / REACH | Restriction of hazardous substances and chemical registration compliance |
7. Unique Selling Points
- Superior Corrosion Resistance: Eliminates the need for protective coatings or anodization, reducing maintenance costs and extending service intervals by 5–10 years compared to bare copper coils.
- Thermal Cycling Durability: Austenitic microstructure retains ductility and resistance to stress corrosion cracking (SCC) under repeated thermal expansion and contraction cycles.
- Hygienic Surface Finish: Bright annealed and passivated surfaces resist biofilm formation and support automated cleaning protocols, making them ideal for food-grade and pharmaceutical applications.
- Customizable Geometry: Wenzhou Jixing offers parametric coil design services, allowing customers to optimize pitch, OD, and WT for specific refrigerant types and heat load requirements.
- Refrigerant Compatibility: Compatible with next-generation low-GWP refrigerants (R-32, R-1234yf, R-290) without risk of chemical degradation or hydrogen embrittlement.
- Full Traceability: Each coil is marked with heat number, material grade, and production date, enabling complete supply chain traceability from raw material to end installation.
8. Technical Notes & Recommendations
Note: When integrating stainless steel evaporator coils into systems with copper or aluminum components, ensure electrical isolation to prevent galvanic corrosion. Use insulated fittings or dielectric gaskets at all dissimilar metal joints. For ammonia (NH₃) systems, verify that the selected grade meets ASME B31.5 requirements for ammonia service.
Installation Guidance: Maintain a minimum bend radius of 3× the outer diameter during on-site routing. Avoid sharp kinks that may compromise wall thickness uniformity and create local stress concentrations susceptible to cracking.
Document prepared in accordance with Wenzhou Jixing Metal Materials Co., Ltd technical documentation standards. For detailed engineering drawings, material certificates, and custom quotation requests, contact the manufacturer's technical sales department