Stainless Steel Coil Tube (Coiltube) — Precision Engineered for HVAC & Critical Environment Systems
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-manufactured tubular product supplied by Wenzhou Jixing Metal Materials Co., Ltd (Wenzhou Jixing), designed specifically for integration into Constant Temperature and Humidity Units (CTHU) and other critical environmental control systems. The Coiltube serves as a core heat exchange element within dehumidification and conditioning assemblies, operating under what is technically classified as Critical Coil Tube Mode — a thermodynamic operating regime in which the coil tube transitions between sensible and latent heat exchange states to maintain precise environmental parameters.
Unlike standard straight-pipe heat exchangers, the Coiltube product family is characterized by its continuous helical or serpentine coil geometry, which maximizes surface-area-to-volume ratio while minimizing pressure drop across the heat transfer medium. This architectural advantage is particularly critical in CTHU applications where simultaneous control of dry-bulb temperature and dew-point humidity is required with tight tolerances (typically ±1.0°C / ±2% RH).
Material & Properties
Base Material
- Primary Alloy: Austenitic Stainless Steel conforming to ASTM A213 / ASTM A269 specifications
- Grade Options: SUS304 (UNS S30400), SUS316L (UNS S31603), SUS321 (UNS S32100)
- Carbon Equivalent: ≤ 0.03% C (for 316L grade, ensuring excellent weldability and resistance to intergranular corrosion)
Mechanical Properties (Typical — Annealed Condition)
| Property | SUS304 | SUS316L | Standard Reference |
|---|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa | ≥ 485 MPa | ASTM A213 / GB/T 12771 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ≥ 170 MPa | ASTM A213 / GB/T 12771 |
| Elongation (延伸率) | ≥ 40% | ≥ 45% | ASTM A269 |
| Thermal Conductivity (导热系数) | 16.3 W/(m·K) @ 20°C | 14.6 W/(m·K) @ 20°C | ASM Handbook Vol. 6 |
| Corrosion Resistance (耐腐蚀性) | Excellent in atmospheric & mild industrial environments | Superior in chloride-containing and high-humidity environments | ASTM G48 (Pitting & Crevice Corrosion) |
Surface Finish Options
- Pickled & Passivated (PP): Standard finish; removes mill scale and forms protective chromium oxide layer
- Baht (2B): Smooth cold-rolled finish suitable for general heat exchange applications
- Polished (No. 4 / Mirror): Available upon request for hygienic or aesthetic applications
Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | Custom diameters available |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | Selected based on operating pressure |
| Coil Pitch (螺旋节距) | 15 mm – 60 mm | Optimized for heat transfer efficiency |
| Coil Diameter (盘管外径) | 100 mm – 800 mm | Dependent on unit footprint |
| Tube Length per Coil (单盘管长度) | 5 m – 150 m | Continuous coil, no joints |
| Operating Pressure (工作压力) | Up to 2.5 MPa (372 psi) | Hydrostatic test at 1.5× working pressure |
| Operating Temperature Range | −40°C to +250°C | SUS321 grade extends to +400°C |
| Refrigerant Compatibility | R-134a, R-407C, R-410A, R-32, R-1234yf, NH₃ | Full compatibility verification available |
| Tolerance on OD | ±0.05 mm (±0.002") | Per ASTM A213 / GB/T 12771 |
| End Form | Plain, Beveled, Flared, or Threaded | Custom configurations available |
Manufacturing Process
Process Flow
- Raw Material Procurement & Inspection: Hot-rolled stainless steel strip or seamless tube stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES), mechanical testing, and visual inspection to verify chemical composition and conform to the specified ASTM/GB grade.
- Slitting & Annealing: Strip is slit to required width and annealed in a continuous belt furnace under controlled hydrogen atmosphere to achieve the desired mechanical properties and eliminate work-hardening stresses.
- Precision Forming (Tube Drawing & Rolling): Seamless tubes are produced via cold-drawing or roll-forming processes. For the coil tube product, precision bending machinery with CNC-controlled roll stations forms the continuous helical or serpentine geometry without introducing kinks, ovality, or wall-thinning beyond acceptable limits (≤ 10% reduction in minimum wall thickness at bend apex).
- Coil Winding & Shaping: The formed tube is wound around mandrels to achieve the specified coil diameter and pitch. Tension control systems ensure uniform spacing and prevent coil-to-coil contact that could cause stress concentration or vibration-induced fatigue.
- Heat Treatment & Stress Relief: Post-forming annealing at 1050°C–1100°C followed by controlled cooling restores full solution-annealed condition, eliminating residual stresses introduced during forming and winding.
- Pickling & Passivation: The coil tube is immersed in a mixed acid solution (HNO₃/HF) to remove surface oxides, followed by a nitric acid passivation step to re-establish a uniform chromium oxide protective film (≥ 200 nm thickness).
- Hydrostatic Pressure Testing: Each coil tube assembly undergoes a hydrostatic test at 1.5× the maximum design working pressure for a minimum dwell time of 5 minutes. Zero leakage is required for acceptance.
- Final Dimensional Inspection & Packaging: Critical dimensions (OD, WT, coil pitch, overall length) are verified using laser measurement systems. Products are wrapped in anti-corrosion protective film and packed in wooden crates or custom fixtures for shipment.
Applications
Primary Application: Constant Temperature and Humidity Units (CTHU)
The Coiltube is the primary heat exchange component in the critical coil tube mode of CTHU systems. In this operating mode, the coil tube functions at the intersection of the sensible and latent heat exchange boundaries — a thermodynamically sensitive regime where precise control of refrigerant flow rate, coil surface temperature, and air-side velocity determines whether the system achieves the target dew point without over-cooling or under-dehumidifying.
Key performance characteristics in this application include:
- High Surface Efficiency: The helical coil geometry provides up to 3.5× greater heat transfer surface area compared to equivalent-length straight tube, enabling compact heat exchangers with high latent heat removal capacity.
- Low Pressure Drop: Continuous smooth bends (no sharp kinks) minimize fluid friction losses, reducing compressor power consumption by 8–15% compared to finned-tube alternatives.
- Corrosion Resistance in Humid Environments: SUS316L grade resists chloride-induced pitting corrosion from continuously saturated air streams, ensuring long service life (≥ 15 years) without degradation of heat transfer performance.
- Thermal Stability: Austenitic stainless steel maintains dimensional stability across the full operating temperature range (−40°C to +250°C), preventing coil deformation or air-gap formation that would compromise airflow distribution.
Secondary Applications
- Industrial Dehumidification Systems: Large-scale process dehumidifiers in pharmaceutical, food processing, and electronics manufacturing facilities
- Cleanroom HVAC Systems: HEPA-filtered air handling units requiring corrosion-resistant heat exchange components
- Refrigeration & Chiller Systems: Evaporators and condensers in commercial refrigeration equipment
- Heat Recovery Systems: Enthalpy wheels and plate-type heat recovery units in energy-efficient building systems
- Process Cooling: Precision temperature control loops in chemical processing and polymer manufacturing
- Marine & Offshore HVAC: Saltwater-resistant air conditioning systems for vessels and offshore platforms
Quality Certifications & Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — covers all manufacturing, inspection, and traceability processes |
| ISO 14001:2015 | Environmental Management System — ensures sustainable production practices and waste minimization |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| ASTM A213 / A269 | Material specification for wrought austenitic stainless steel seamless tubes and cold-drawn tubes |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes for general application |
| ASME B31.9 | Pressure piping code for refrigeration and air-conditioning systems (applicable to Coiltube integration) |
| EN 10217-7 | European standard for seamless stainless steel tubes for pressure purposes |
| RoHS 2.0 (EU 2011/65/EU) | Restriction of Hazardous Substances — all materials comply with EU directive limits |
| REACH (EU 1907/2006) | Registration, Evaluation, Authorisation and Restriction of Chemicals compliance |
| NACE MR0175 / ISO 15156 | Material requirements for equipment in H₂S-containing environments (available for specialty grades) |
Unique Selling Points
1. Critical Mode Optimization: The Coiltube geometry is specifically engineered for operation in the thermodynamically critical zone of CTHU systems, where conventional straight-tube heat exchangers suffer from instability and poor humidity control. The helical configuration provides inherent flow maldistribution correction and uniform heat flux distribution across the entire coil surface.
2. Seamless Continuous Construction: Unlike assembled coil products that rely on brazed or welded joints between tube segments, Wenzhou Jixing Coiltubes are formed from a single continuous length of seamless tube. This eliminates potential leak points, reduces maintenance requirements, and extends service life significantly.
3. Precision CNC Coil Winding: Computer Numerical Control (CNC) winding machinery ensures dimensional accuracy of coil pitch, diameter, and overall geometry within ±0.5 mm tolerance. This precision is critical for proper integration into pre-engineered CTHU chassis and for maintaining designed airflow patterns.
4. Material Grade Flexibility: The product line offers SUS304, SUS316L, and SUS321 grades, allowing customers to select the optimal material balance between cost, corrosion resistance, and temperature capability for their specific application environment.
5. Full Traceability & Documentation: Every Coiltube unit is accompanied by a Material Test Certificate (MTC) in accordance with EN 10204 Type 3.1, providing complete traceability from raw material heat number through all manufacturing and inspection stages.
Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd offers comprehensive engineering support for Coiltube integration into CTHU and other HVAC systems, including:
- Thermal-hydraulic performance simulation (CFD & 1D modeling) for custom coil configurations
- Refrigerant compatibility analysis and system-level thermodynamic optimization
- Custom coil geometry design based on unit footprint, capacity, and airflow constraints