Stainless Steel Coil Tube (Coiltube) — Three-Row Variable Fin-Spacing Evaporator Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled heat transfer component designed for advanced evaporator and heat exchanger systems. This product series is specifically optimized for three-row variable fin-spacing configurations, where the coil tube serves as the core flow channel for refrigerant circulation. The coil tube is formed through continuous bending of seamless stainless steel tubing into tightly wound helical or serpentine patterns, enabling compact heat exchange geometries with high surface-area-to-volume ratios.
Derived from rigorous research on frosting characteristics in three-row variable fin-spacing coil tube evaporators, this product line incorporates design refinements that address frost accumulation dynamics, airflow distribution uniformity, and heat transfer degradation under humid operating conditions. The coil tube geometry is engineered to minimize differential pressure across rows while maximizing convective heat transfer coefficients, particularly in dehumidification and low-temperature defrost cycles.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected for its exceptional corrosion resistance, mechanical integrity, and long-term thermal stability across a wide operating temperature range.
- Primary Alloy Grades: SUS304 (AISI 304), SUS316 (AISI 316), SUS316L (AISI 316L), and SUS321 (AISI 321) depending on application-specific corrosion and temperature requirements.
- Corrosion Resistance: The chromium (Cr ≥ 18%) and nickel (Ni ≥ 8%) content in the 304 grade provides robust resistance to atmospheric corrosion, mild acids, and alkaline solutions. The 316L grade offers superior resistance to chloride-induced pitting and crevice corrosion through the addition of molybdenum (Mo ≥ 2%).
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20°C for SUS304, providing reliable heat transfer performance without the need for additional thermal enhancement coatings.
- Mechanical Properties: Tensile strength of ≥ 520 MPa (annealed condition) with elongation ≥ 40%, ensuring the tubing withstands the mechanical stresses of coiling, welding, and operational vibration without deformation or fatigue failure.
- Temperature Range: Continuous operating capability from −196°C (cryogenic applications) to +870°C (oxidation-resistant environments), with no risk of embrittlement or phase transformation within the austenitic structure.
- Hygienic Surface: Inner surface roughness (Ra) ≤ 0.4 μm available upon request for food-grade and pharmaceutical applications, preventing bacterial adhesion and facilitating clean-in-place (CIP) procedures.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.0 mm / 7.0 mm / 8.0 mm / 9.53 mm / 12.0 mm (custom sizes available) | ASTM A213 / GB/T 12771 |
| Tube Wall Thickness | 0.5 mm – 1.5 mm (tolerance ±10%) | ASTM A213 / EN 10217 |
| Coil Inner Diameter | 50 mm – 500 mm (configurable per design requirement) | Custom / OEM Specification |
| Coil Length (Uncoiled) | Up to 12,000 mm per continuous run | — |
| Number of Rows | 1 to 3 rows (optimized for three-row variable fin-spacing configurations) | Design-specific |
| Fin Spacing (Variable) | 1.4 mm – 3.2 mm (graded distribution across coil face) | Research-optimized profile |
| Fin Material | Aluminum (Al 1100 / Al 3003) or Stainless Steel (SUS304) corrugated fins | ASTM B209 / ASTM B209M |
| Refrigerant Compatibility | R134a, R404A, R407C, R410A, R32, R1234yf, CO₂ (R744) | ASHRAE 34 |
| Maximum Operating Pressure | 4.0 MPa (design); 6.0 MPa (test) | EN 1273 / ASME BPV |
| Hydrostatic Test Pressure | 1.5 × maximum operating pressure (held for 30 minutes) | ISO 11114-1 |
| Surface Finish (Outer) | Bright annealed / Passivated (Ra ≤ 0.8 μm) | ASTM A967 |
| Surface Finish (Inner) | Bright annealed (Ra ≤ 0.4 μm) or electropolished (Ra ≤ 0.2 μm) | ASTM A967 / Custom |
| Welding Process | Orbital TIG (GTAW) with argon internal shielding | ISO 15614-1 / ASME IX |
| Heat Transfer Efficiency | Enhanced by 15%–25% compared to uniform fin-spacing baselines | Empirical / CFD-validated |
Manufacturing Process
The production of the Stainless Steel Coil Tube follows a tightly controlled, multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and functional performance:
- Raw Material Inspection: Incoming stainless steel tubes are verified against mill certificates (EN 10204 Type 3.1) for chemical composition, mechanical properties, and surface quality. Spectroscopic analysis (PMI — Positive Material Identification) confirms alloy grade compliance.
- End Preparation & Deburring: Tube ends are mechanically deburred and chamfered to eliminate burrs that could impede refrigerant flow or damage downstream components.
- Hydrostatic Pre-Test: Each tube segment undergoes a hydrostatic pressure test at 1.5× the maximum operating pressure to identify any micro-defects or wall thinning prior to forming.
- Precision Coiling: Tubes are fed through CNC-controlled coiling machines equipped with mandrel-guided forming dies. The coiling process maintains a consistent bend radius (minimum 5× tube OD) to prevent ovality exceeding 2% and to avoid work-hardening or residual stress accumulation in the bend zones.
- Fin Application (if applicable): Variable fin-spacing aluminum or stainless steel fins are mechanically crimped onto the coil tube using precision finning equipment. The fin spacing is programmatically varied across the coil face — typically denser at the inlet section (1.4–1.8 mm pitch) and progressively relaxed toward the outlet (2.4–3.2 mm pitch) — to optimize airflow distribution and reduce frosting propensity in the rear rows.
- Orbital TIG Welding: Header connections and U-bend return joints are fabricated using automated orbital TIG welding with continuous argon internal shielding (minimum 99.99% purity). Weld parameters are calibrated to minimize heat input and prevent sensitization or carbide precipitation at weld zones.
- Passivation & Cleaning: Post-weld passivation treatment removes chromium-depleted heat-affected zones and establishes a stable chromium oxide protective film. The interior is cleaned using acid pickling or electropolishing to achieve the specified surface roughness.
- Final Quality Assurance: Each coil tube assembly undergoes 100% hydrostatic pressure testing, visual inspection of weld joints (including dye penetrant testing for critical connections), and dimensional verification using coordinate measuring machines (CMM) or laser scanning.
Applications
The Stainless Steel Coil Tube is designed for demanding thermal management applications where corrosion resistance, hygiene, and long service life are paramount:
- Commercial & Industrial Refrigeration: Low-temperature evaporators, blast freezers, cold room cooling units, and walk-in cooler systems operating with various refrigerants including R404A, R410A, and R744 (CO₂ transcritical systems).
- Food Processing & Dairy Equipment: Milk pasteurization heat exchangers, cheese aging room evaporators, and beverage cooling systems requiring food-grade (FDA-compliant) materials and hygienic surface finishes.
- Pharmaceutical & Biotechnology: Cold chain storage systems, vaccine refrigeration units, and laboratory cold rooms where GMP (Good Manufacturing Practice) standards mandate corrosion-resistant, cleanable construction.
- Air Conditioning & HVAC: Multi-split outdoor units, VRF (Variable Refrigerant Flow) system condensers and evaporators, and heat pump coils where the variable fin-spacing design reduces frosting-related capacity degradation.
- Marine & Offshore Environments: Cooling coils for marine HVAC systems and offshore platform utilities, leveraging the chloride resistance of SUS316L grade to withstand salt spray and high-humidity conditions.
- Cryogenic Applications: Liquid nitrogen cooling systems, LNG (Liquefied Natural Gas) pre-coolers, and aerospace thermal management systems requiring reliable performance at temperatures below −150°C.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets or exceeds international standards:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing processes from raw material procurement to final dispatch.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices and waste minimization.
- CE Marking — Compliance with EU Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU) for products operating under pressure.
- ASME / NB Stamp — American Society of Mechanical Engineers National Board registration for pressure-containing components manufactured to ASME BPV Code Section I or VIII.
- EN 1273 — European standard compliance for refrigeration system components, including material specifications, manufacturing tolerances, and pressure testing protocols.
- ISO 11114-1 — Conformity with international refrigeration and heat pump safety standards for component design, manufacture, and marking.
- 3-A Sanitary Standards — Available for food-grade applications, ensuring hygienic design and fabrication suitable for dairy, beverage, and pharmaceutical processing.
- Mill Test Certificates (MTC) — EN 10204 Type 3.1 certificates provided with each shipment, documenting chemical analysis, mechanical test results, and traceability of raw materials to the original heat number.
Unique Selling Points
Research-Driven Variable Fin-Spacing Optimization: This coil tube series is the product of dedicated academic research into frosting characteristics of three-row variable fin-spacing evaporators. The non-uniform fin distribution — denser at the coil inlet and progressively relaxed downstream — has been empirically demonstrated to reduce frost accumulation by up to 30% compared to conventional uniform-spacing designs, thereby extending defrost cycle intervals, improving seasonal energy efficiency (SEER/EER), and reducing compressor cycling frequency.
- Superior Corrosion Longevity: Full stainless steel construction (SUS304/SUS316L) eliminates the galvanic corrosion risks inherent in copper-aluminum heat exchangers, extending service life to 25+ years even in aggressive chemical or marine environments.
- Wide Refrigerant Compatibility: Engineered to handle next-generation low-GWP refrigerants (R32, R1234yf, R290) and CO₂ transcritical systems without material compatibility concerns, ensuring future-proofing as the industry transitions away from high-GWP refrigerants.
- Cryogenic to High-Temperature Versatility: The austenitic stainless steel matrix maintains ductility and strength from cryogenic temperatures to elevated process temperatures, enabling a single material platform for diverse thermal applications.
- Hygienic & Food-Safe Design: Available with electropolished inner surfaces (Ra ≤ 0.2 μm) and crevice-free orbital welds, meeting the most stringent food safety and pharmaceutical hygiene requirements without additional coatings or linings.
- Customizable Geometry: Full parametric customization of coil OD, wall thickness, coil diameter, row configuration, and fin spacing profiles to meet OEM-specific thermal and spatial constraints.
- Traceability & Quality Assurance: Every coil tube is traceable to its raw material heat number, with comprehensive testing documentation (hydrostatic, dimensional, visual, and material verification) provided per shipment.
Technical Summary
The Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd. represents a convergence of metallurgical science, thermal engineering research, and precision manufacturing. By integrating variable fin-spacing design principles validated through frosting characteristic studies into a robust stainless steel coil tube platform, this product delivers superior heat transfer performance, extended defrost-free operation, and unmatched material durability. It is the preferred solution for applications where reliability, hygiene, and energy efficiency are non-negotiable requirements.