Stainless Steel Coil Tube (Coiltube) — Refrigeration Evaporator Grade
Product Reference No.: 1710 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous-length tubing product designed specifically for refrigeration and thermal management applications. Unlike straight pipe segments, coil tubes are formed into continuous helical or serpentine configurations, enabling compact heat-exchange geometries with maximized surface-area-to-volume ratios. This product line is purpose-built for household refrigerator coil-type evaporators, where efficient latent-heat transfer and long-term corrosion resistance are critical performance parameters.
Wenzhou Jixing Metal Materials Co., Ltd. supplies coil tubes that serve as the primary heat-exchange medium in evaporator assemblies, facilitating the phase-change cycle of refrigerants (e.g., R600a, R134a) within domestic refrigeration systems. The continuous coil form factor eliminates the need for external bends and brazed joints, thereby reducing leak risk and improving system reliability over the product lifecycle.
2. Material & Properties
2.1 Base Material Grades
- 304 Stainless Steel (UNS S30400 / AISI 304): The predominant grade for food-contact and household refrigeration coil tubes. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni), offering excellent general corrosion resistance, weldability, and ductility.
- 316 Stainless Steel (UNS S31600 / AISI 316): An enhanced grade incorporating 2–3% Molybdenum (Mo), providing superior resistance to chloride-induced pitting and crevice corrosion in demanding environments.
- 304L Stainless Steel (UNS S30403): A low-carbon variant (C ≤ 0.03%) suitable for applications requiring extensive welding without sensitization risk.
2.2 Mechanical Properties (Typical — 304 Grade, Annealed Condition)
- Tensile Strength (UTS): ≥ 515 MPa (75 ksi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (30 ksi)
- Elongation at Break: ≥ 40%
- Hardness: ≤ 92 HRB (annealed); ≤ 102 HRB (cold-worked)
- Density: 8.0 g/cm³
2.3 Thermal & Physical Properties
- Thermal Conductivity (25°C): 16.3 W/(m·K)
- Specific Heat Capacity: 500 J/(kg·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /K
- Operating Temperature Range: −196°C to +870°C (continuous service)
2.4 Surface Finish Options
- 2B (Cold Rolled & Bright Annealed): Standard finish for general refrigeration coil applications; smooth, matte appearance with good formability.
- No. 4 Brushed: Fine linear grain pattern; suitable for semi-exposed installations.
- Electropolished (EP): Ra ≤ 0.4 μm; hygienic-grade finish for food-processing refrigeration systems.
- Mirror Polish (8K): Ra ≤ 0.1 μm; decorative and high-end commercial applications.
3. Technical Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 12.0 mm (customizable) | ASME B36.19M |
| Wall Thickness (WT) | 0.3 mm – 1.2 mm | ASTM A213 / A269 |
| Coil Diameter (CD) | 150 mm – 600 mm (helical pitch adjustable) | Manufacturer Specification |
| Helical Pitch (P) | 8 mm – 25 mm (configurable per evaporator design) | — |
| Coil Length per Spool | 50 m – 200 m (standard); up to 500 m on request | — |
| Dimensional Tolerance (OD) | ±0.05 mm (fine tolerance); ±0.10 mm (standard) | ISO 4427 |
| Dimensional Tolerance (WT) | ±10% of nominal | ASTM A269 |
| Roundness Tolerance | ≤ 10% of OD tolerance | ASME B36.19M |
| Straightness (uncoiled) | ≤ 1.5 mm/m | ISO 1128 |
| Maximum Working Pressure | ≥ 2.5 MPa (362.6 psi) at 20°C | ASME B31.1 |
| Hydrostatic Test Pressure | 1.5 × Maximum Working Pressure | ASME B31.1 |
| Refrigerant Compatibility | R600a, R134a, R404A, R410A, CO₂ (R744) | ASHRAE Standard 34 |
| Food Contact Compliance | US FDA 21 CFR 175.300; EU 1935/2004 | — |
| Coating / Lining | Optional: PTFE (Teflon®) inner lining, passivated surface | — |
| Packaging | Wooden pallet with VCI (Vapor Corrosion Inhibitor) film; moisture-barrier wrapping | ISO 4180 |
4. Manufacturing Process
4.1 Process Flowchart (Summary)
- Raw Material Selection: Hot-rolled stainless steel strip (coil) conforming to ASTM A240 chemical composition requirements.
- Acid Pickling & Passivation: Removal of mill scale via mixed-acid immersion (HNO₃/HF); subsequent passivation to establish a stable chromium-oxide passive film (Cr₂O₃, thickness 2–5 nm).
- Cold Rolling (Cold Reduction): Multi-pass cold rolling to achieve target OD and WT with controlled work-hardening. Intermediate annealing at 1050–1100°C in protective atmosphere (N₂ + H₂) to restore ductility.
- Tube Forming (Seamless or Welded):
- Seamless route: Pierce-and-elongate (Plattner-type) or rotary-perforation methods for high-pressure applications.
- Welded route: ERW (Electric Resistance Welding) or TIG (Tungsten Inert Gas) welding with full penetration; internal and external weld bead grinding to achieve Ra ≤ 0.8 μm at weld zone.
- Precision Sizing: Cold-drawing through calibrated tungsten-carbide (WC) dies to achieve tight dimensional tolerances (±0.05 mm OD).
- Final Annealing: Solution annealing at 1050°C in vacuum or dew-point-controlled atmosphere (dew point ≤ −60°C); controlled cooling to prevent intergranular corrosion sensitization (avoiding the 450–850°C range).
- Coil Forming (Bending): Multi-axis CNC bending machine forms the continuous tube into helical or serpentine coil geometry. Bending radii are controlled to prevent wall-thinning (>15% reduction prohibited) and ovality distortion (>8% prohibited).
- Dimensional & Visual Inspection: Laser OD measurement, ultrasonic wall-thickness gauging, dye-penetrant inspection (DPI) of weld seams.
- Pressure Testing: Hydrostatic pressure testing at 1.5× MWP for a minimum dwell time of 30 seconds per coil length.
- Surface Treatment: Final passivation, optional electropolishing, and/or PTFE inner-surface coating application.
- Coiling & Packaging: Winding onto precision steel reels; VCI film wrapping; moisture-barrier outer packaging; labeling with batch traceability data.
4.2 Key Process Parameters
- Minimum Bending Radius: 3.0 × OD (standard); 2.5 × OD (with internal mandrel support)
- Maximum Bending Speed: 2.0 m/min (to prevent localized work-hardening and micro-cracking)
- Coil Pitch Accuracy: ±0.5 mm
- Coil Diameter Accuracy: ±2.0 mm
5. Applications
5.1 Primary Applications
- Household Refrigerator Evaporators: The coil tube serves as the refrigerant flow channel within the evaporator assembly, facilitating heat absorption from the refrigerated compartment. The continuous coil geometry enables compact packaging within the refrigerator's rear or top compartment while maintaining high heat-transfer efficiency.
- Freezer Compartment Evaporators: Deep-freeze sections (−18°C to −24°C) require coil tubes with enhanced low-temperature ductility and fatigue resistance; 304L or 316 grade is recommended for extended service life.
- Ice-Maker Modules: Compact coil tubes with reduced OD (3–5 mm) used in integrated ice-making units within refrigerator doors.
5.2 Secondary Applications
- Commercial Refrigeration: Display cases, walk-in coolers, and blast freezers requiring high-efficiency evaporator coils.
- Heat-Exchange Coils: Air-conditioning evaporator and condenser coils where stainless steel corrosion resistance is mandated (e.g., coastal or industrial environments).
- Food-Processing Equipment: CIP (Clean-In-Place) compatible evaporator assemblies in dairy, beverage, and pharmaceutical processing.
- Cryogenic Systems: Sub-zero applications down to −196°C (liquid nitrogen) where austenitic stainless steel retains full mechanical properties.
6. Quality Certifications & Compliance
6.1 Manufacturing Quality System
- ISO 9001:2015: Quality Management System certification covering the entire manufacturing value chain.
- ISO 14001:2015: Environmental Management System certification for sustainable production practices.
- ISO 45001:2018: Occupational Health and Safety Management System.
6.2 Product-Specific Certifications
- EN 10204 Type 3.1: Third-party inspection certificate with full test report (chemical analysis, mechanical test results, dimensional measurements).
- Mill Test Certificate (MTC): Provided with every shipment, documenting heat number, chemical composition, mechanical properties, and traceability.
- ASME B36.19M: Conformity with dimensions and tolerances for wrought stainless steel pipe and tube.
- ASTM A269: Standard specification for seamless and welded austenitic stainless steel tubing for chemical and heat-exchange applications.
- ASTM A213: Standard specification for seamless austenitic stainless steel tubing for boiler, heat-exchanger, and similar heat-absorbing applications.
- CE Marking: Conformity with European Directive 2014/68/EU (Pressure Equipment Directive) for pressure-containing components.
- RoHS 2.0 (EU 2011/65/EU): Restriction of Hazardous Substances compliance.
- REACH (EU 1907/2006): Registration, Evaluation, Authorisation and Restriction of Chemicals compliance.
- US FDA 21 CFR 175.300: Food-contact material safety certification for austenitic stainless steel.
- EU Regulation 1935/2004: Framework Regulation for Materials and Articles Intended to Come into Contact with Food.
- NF T 55-145: French standard for stainless steel food-contact surfaces (applicable for European market entry).
6.3 Inspection & Testing Protocols
- Chemical Analysis: Spark-OES (Optical Emission Spectroscopy) or ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) for full elemental verification.
- Grain Structure Analysis: Metallographic examination per ASTM E45 to verify annealed austenitic microstructure.
- Corrosion Testing: Salt-spray testing (ASTM B117, 500 hours minimum), intergranular corrosion testing (AST