Stainless Steel Coil Tube — Air Conditioning Unit Coil Section
Product Code: JX-CT-1196 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Classification: Technical Reference & Engineering Design Literature
This document serves as a comprehensive technical specification for the Stainless Steel Coil Tube product line, derived from research and engineering studies on auxiliary design methodologies for air conditioning unit coil sections. The product represents a specialized form of stainless steel tubing engineered for efficient thermal exchange in HVAC (Heating, Ventilation, and Air Conditioning) systems.
1. Product Overview
The Stainless Steel Coil Tube (盘管) is a precision-engineered tubing product manufactured in continuous coiled form, specifically designed for integration into air conditioning units, heat exchangers, and thermal management systems. Unlike straight-length stainless steel pipes, coil tubes are produced as continuous helical coils that are subsequently cut, formed, and assembled into compact heat exchange configurations.
The research foundation for this product line stems from the study titled "Auxiliary Design Research on Coil Sections of Air Conditioning Units" (《空调机组盘管段辅助设计研究》), which addressed critical challenges in coil section design including:
- Thermal Efficiency Optimization: Maximizing heat transfer coefficients while minimizing pressure drop across the coil section
- Structural Integrity: Ensuring mechanical stability under cyclic thermal loading and operational vibration
- Manufacturing Feasibility: Developing practical coil winding parameters that balance dimensional accuracy with production throughput
- Material Selection: Evaluating stainless steel grades for corrosion resistance, thermal conductivity, and long-term durability in aggressive environmental conditions
Wenzhou Jixing Metal Materials Co., Ltd. leverages these research findings to produce coil tubes that meet or exceed international standards for HVAC applications, offering superior performance characteristics compared to conventional carbon steel or copper alternatives in specific operating environments.
2. Material & Properties
2.1 Base Material Grades
The coil tube product line is manufactured from high-quality austenitic and duplex stainless steel grades, selected based on application-specific requirements:
| Grade Designation | UNS Number | Equivalent Standard | Key Application |
|---|---|---|---|
| SUS304 / 304 | UNS S30400 | ASTM A269 / EN 10217-7 | General HVAC coil sections, moderate corrosion environments |
| SUS316 / 316L | UNS S31600 / S31603 | ASTM A269 / EN 10217-7 | Marine, chemical, and high-chloride HVAC applications |
| SUS321 / 321 | UNS S32100 | ASTM A269 / EN 10217-7 | High-temperature air conditioning and heat recovery systems |
| SUS316Ti | UNS S31635 | ASTM A269 / EN 10217-7 | Welded coil assemblies requiring high-temperature stability |
| 2205 Duplex | UNS S31803 | ASTM A269 / EN 10217-7 | High-stress, high-corrosion HVAC environments |
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property | SUS304 | SUS316L | SUS321 | 2205 Duplex |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 | ≥ 520 | ≥ 550 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ≥ 205 | ≥ 450 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 25 |
| Thermal Conductivity (W/m·K @ 20°C) | 16.3 | 14.6 | 16.3 | 13.5 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −196 to +900 | −50 to +350 |
2.3 Corrosion Resistance
Stainless steel coil tubes exhibit exceptional resistance to atmospheric corrosion, condensation water, and mild chemical exposure — critical properties for air conditioning coil sections where moisture, refrigerants, and ambient contaminants are present. The passive chromium oxide layer (Cr₂O₃) self-heals under normal operating conditions, providing long-term protection without the need for additional coatings or treatments.
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ±0.15 mm | ASTM A269 / EN 10217-7 |
| Wall Thickness (WT) | 0.30 mm – 3.00 mm | ±10% of nominal | ASTM A269 / EN 10217-7 |
| Coil Winding Diameter | 150 mm – 1,200 mm | ±5 mm | Manufacturer specification |
| Coil Length (per roll) | 5 m – 200 m | As ordered | Manufacturer specification |
| Straight Section Length | 1,000 mm – 6,000 mm (cut-to-length) | ±10 mm | ASTM A269 |
| Surface Finish | 2B / No. 4 / BA (Bright Annealed) | Ra ≤ 0.8 μm | ASTM A269 / EN 10217-7 |
| End Condition | Plain / Beveled / Threaded / Flanged | As specified | Per customer drawing |
3.2 Coil Section Design Parameters (Air Conditioning Application)
| Design Parameter | Typical Value | Engineering Rationale |
|---|---|---|
| Tube Pitch (Axial) | 1.25× OD – 1.5× OD | Optimizes airflow resistance vs. heat transfer area |
| Tube Pitch (Transverse) | 1.25× OD – 1.5× OD | Ensures uniform air distribution across coil face |
| Fin Spacing | 1.5 mm – 3.0 mm | Balances fin surface area with fouling resistance |
| Row Depth | 2 – 8 rows | Determined by required temperature change and airflow |
| Refrigerant Flow Velocity | 1.0 – 3.0 m/s | Minimizes pressure drop while maintaining heat transfer |
| Design Pressure (Refrigerant Side) | Up to 4.0 MPa (580 psi) | Compliant with ASHRAE and ISO refrigeration standards |
| Design Pressure (Air Side) | Up to 2.5 kPa (0.025 bar) | Typical for forced-convection air handling units |
3.3 Compliance Standards
| Standard | Title | Scope |
|---|---|---|
| ASTM A269 / A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing | Material and dimensional requirements |
| EN 10217-7 | Non-ferrous metallic materials — Seamless tubes for pressure purposes | European material specification |
| GB/T 12771 | Non-alloy and alloy steel seamless tubes and hollow profiles | Chinese national standard (stainless steel variant) |
| ISO 2852 | Stainless steel seamless tubes for pressure purposes | International dimensional and material standard |
| ASHRAE Standard 15 | Pressure Vessel Code for Refrigeration Systems | Pressure vessel design for refrigerant coils |
| EN 12952 | Heat exchangers — Plate-fin heat exchangers | Thermal performance requirements |
4. Manufacturing Process
4.1 Production Workflow
The manufacturing process for stainless steel coil tubes follows a rigorous multi-stage workflow designed to ensure dimensional precision, metallurgical integrity, and surface quality:
- Raw Material Inspection & Milling: Ingot casting or strip rolling of certified stainless steel stock. Incoming material is verified via spectroscopic analysis (OES — Optical Emission Spectroscopy) to confirm chemical composition compliance with the specified grade.
- Hot Rolling & Annealing: Strip or tube blank material is hot-rolled to approximate dimensions and subsequently annealed at 1,050°C – 1,150°C to relieve internal stresses and achieve the desired austenitic microstructure.
- Pickling & Passivation: The annealed material undergoes acid pickling (typically using a mixed HNO₃/HF or citric acid solution) to remove mill scale and oxide deposits, followed by passivation to restore the protective chromium oxide layer.
- Cold Drawing / Cold Forming: The tube blank is cold-drawn through precision dies to achieve final OD and wall thickness dimensions. This process enhances mechanical properties (work hardening) and achieves the required dimensional tolerances.
- Coil Winding: The formed tube is wound into a continuous coil using automated winding equipment. Winding parameters — including coil diameter, tension, and layer configuration — are controlled to prevent kinking, flattening, or surface damage.
- Intermediate Annealing (if required): For multi-pass cold forming operations, intermediate annealing may be performed to restore ductility and prevent cracking.
- Final Annealing & Pickling: A final anneal cycle ensures the material is in the fully annealed (A) condition with optimal corrosion resistance and mechanical properties.
- Quality Inspection: Each coil undergoes dimensional verification (OD, WT via ultrasonic or laser measurement), surface inspection, and hydrostatic pressure testing (typically at 2.5× working pressure for a minimum of 5 seconds).
- Packaging & Dispatch: Inspected coils are protected with VCI (Vapor Corrosion Inhibitor) paper wrapping, banded, and palletized for shipment.
4.2 Coil Section Assembly Process
For air conditioning unit coil sections, the coil tube is further processed as follows:
- Tube Cutting & Forming: Coil tube is cut to required lengths and U-bent at specified radii to form serpentine tube passes.
- Fin Attachment: Aluminum or stainless steel fins are stamped and inserted between tube rows (fin-and-tube configuration) or the tube surface is mechanically expanded to create integral fins.
- Header Welding: Tube ends are brazed or welded to stainless steel headers (distributors and collectors) using TIG (Tungsten Inert Gas) welding or vacuum brazing.
- Pressure Testing: The assembled coil section undergoes pneumatic or hydraulic pressure testing to verify leak-tightness and structural integrity.
- Performance Testing: Selected samples undergo thermal performance testing in a calibrated wind tunnel to verify heat transfer coefficients (UA values) against design specifications.
5. Applications
5.1 Primary Application Domains
- Commercial Air Conditioning Units: Evaporator and condenser coil sections in rooftop units (RTUs), packaged terminal air conditioners (PTACs), and modular air handling units (AHUs). The stainless steel construction provides superior resistance to condensate corrosion compared to copper alternatives.
- Industrial Process Cooling: Heat exchangers in chemical processing, food and beverage manufacturing, and pharmaceutical production where aggressive process fluids require corrosion-resistant tubing.
- Marine HVAC Systems: Air conditioning units for ships, yachts, and offshore platforms where salt-laden atmospheres demand high-grade stainless steel (316L or 2205 Duplex) for long-term reliability.
- Refrigeration Systems: Cold storage evaporators, walk-in cooler coils, and refrigeration condenser units where stainless steel tubing provides durability and hygiene compliance.