Stainless Steel Coil Tube for Central Air Conditioning Preheating Systems
Product Overview
The stainless steel coil tube (盘管 / Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed specifically for preheating coil assemblies in central air conditioning (Central Air Conditioning, CAC) units. These coil tubes serve as the critical heat exchange medium within preheating sections, where they facilitate thermal transfer to prevent freezing conditions in downstream coils during low-load or defrost cycles. The product is engineered to withstand repeated thermal cycling, corrosion exposure from humid air streams, and mechanical stress associated with coil winding and installation.
The coil tube system plays an indispensable role in the anti-freeze control method (防冻控制方法) employed in modern central air conditioning units. By ensuring adequate preheating of the refrigerant or water circuit before it enters the main evaporator or condenser coil, these stainless steel tubes effectively mitigate the risk of ice formation, thereby protecting the integrity of the entire HVAC system and maintaining operational efficiency.
Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel, selected for its superior combination of corrosion resistance, thermal conductivity, and mechanical durability under HVAC operating conditions.
Primary Material Grades
- SUS 304 / AISI 304 — General-purpose austenitic stainless steel with excellent corrosion resistance and formability; suitable for standard HVAC preheating applications.
- SUS 316 / AISI 316 — Enhanced austenitic stainless steel with added molybdenum (Mo) content, providing superior resistance to pitting and crevice corrosion in humid or chemically aggressive environments.
- SUS 321 / AISI 321 — Titanium-stabilized austenitic stainless steel offering improved resistance to intergranular corrosion at elevated temperatures, suitable for high-temperature preheating circuits.
Key Physical and Mechanical Properties
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa | ASTM E8 / ASTM A269 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ASTM E8 |
| Thermal Conductivity (热导率) | 14–16 W/(m·K) at 20°C | ASTM E153 |
| Elongation (延伸率) | ≥ 40% | ASTM E8 |
| Density (密度) | 7.93 g/cm³ | — |
| Operating Temperature Range (工作温度范围) | −40°C to +350°C | — |
| Corrosion Resistance (耐蚀性) | Excellent in atmospheric, aqueous, and humid environments | ASTM G48 / Salt Spray Test |
Specifications
| Parameter | Specification / Range | Notes |
|---|---|---|
| Product Designation | CAT-SX-422 Series | Internal catalog reference No. 422 |
| Outer Diameter (OD) | 6.35 mm – 19.05 mm (¼" – ¾") | Custom sizes available upon request |
| Wall Thickness (壁厚) | 0.5 mm – 1.5 mm | Tolerance: ±0.05 mm |
| Coil Winding Diameter (盘绕直径) | 50 mm – 500 mm | Dependent on application geometry |
| Tube Length per Coil (单圈管长) | 10 m – 100 m | Continuous seamless or welded |
| Surface Finish (表面光洁度) | Mirror polish (Ra ≤ 0.4 μm) or standard pickled & passivated | ASTM A269 / ASTM A270 |
| Tolerance on OD (外径公差) | ±0.1 mm | ISO 4407 |
| Pressure Rating (耐压等级) | Up to 1.6 MPa (standard) / 4.0 MPa (reinforced) | Hydrostatic test verified |
| Heat Exchanger Configuration (换热器构型) | Single-pass, double-pass, or multi-pass coil winding | Customizable per system design |
| Connection Method (连接方式) | Flare, brazed, welded, or threaded fittings | Compatible with standard HVAC fittings |
| Standards Compliance (标准合规) | ASTM A269, ASTM A270, GB/T 14976, EN 10216-5 | Mutually exclusive per order |
Manufacturing Process
The production of the CAT-SX-422 series coil tubes follows a rigorously controlled multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability:
- Raw Material Selection & Verification (原材料选型与检验) — Austenitic stainless steel wire rod or seamless tube blanks are procured from certified mills and subjected to incoming inspection, including chemical composition analysis (光谱分析) via Optical Emission Spectrometry (OES) and mechanical property verification.
- Hot Rolling & Annealing (热轧与退火) — Raw stock is hot-rolled to approximate dimensions and subsequently annealed in a controlled atmosphere to achieve the desired grain structure and relieve residual stresses.
- Precision Cold Drawing (精密冷轧) — The tube is cold-drawn through calibrated dies to achieve the final outer diameter and wall thickness within specified tolerances. This process enhances mechanical strength and surface finish.
- Pickling & Passivation (酸洗与钝化) — The drawn tube undergoes acid pickling to remove surface scale and contaminants, followed by passivation treatment to form a protective chromium oxide layer (Cr₂O₃), enhancing corrosion resistance.
- Coil Winding (盘绕成型) — The straight tube is mechanically wound into the required coil geometry using CNC-controlled winding equipment. The winding process ensures uniform tension distribution and consistent coil diameter throughout the length.
- Hydrostatic Pressure Testing (水压试验) — Each coil tube assembly is subjected to hydrostatic pressure testing at 1.5× the maximum operating pressure to verify structural integrity and detect any potential leaks or defects.
- Final Inspection & Quality Assurance (最终检验与质量保证) — Comprehensive final inspection includes dimensional verification, surface quality assessment, visual examination for weld integrity, and material certification documentation.
Applications
The CAT-SX-422 stainless steel coil tube is purpose-designed for the following application domains:
- Central Air Conditioning Preheating Systems (中央空调机组预热系统) — Primary application; the coil tube forms the heat exchange element in preheating sections, ensuring that fluid entering the main evaporator is at a sufficient temperature to prevent freezing. This is integral to the anti-freeze control methodology (防冻控制方法) in commercial and industrial HVAC systems.
- VRF (Variable Refrigerant Flow) Systems — Used in preheating and defrost coils within variable refrigerant flow air conditioning systems where precise temperature management is critical.
- Chiller Units (冷水机组) — Employed in evaporator and condenser coil assemblies within centrifugal and screw chiller units for commercial buildings.
- Heat Recovery Units (热回收机组) — Integral to heat recovery air handling units where thermal energy is transferred between exhaust and supply air streams.
- Industrial Process Cooling — Applicable in industrial cooling circuits where corrosion resistance and long service life are required.
Anti-Freeze Control Methodology (防冻控制方法): In central air conditioning systems, the preheating coil tube assembly operates in conjunction with temperature sensors and control valves to maintain the refrigerant or water circuit temperature above the freezing threshold (0°C for water-based systems). When the system detects a risk of ice formation on the main coil, the preheating circuit activates, routing warmer fluid through the stainless steel coil tubes to raise the inlet temperature. This proactive thermal management prevents coil frosting, maintains heat exchange efficiency, and extends the operational lifespan of the entire HVAC system.
Quality Certifications & Standards
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification, ensuring systematic quality control across all production stages.
- ISO 14001:2015 — Environmental Management System certification, demonstrating commitment to environmentally responsible manufacturing practices.
- ASTM A269 — Specification for seamless austenitic stainless steel tubing for general applications.
- ASTM A270 — Specification for seamless and welded austenitic stainless steel tubing for chemical and heat-exchange equipment.
- GB/T 14976 — Chinese national standard for seamless stainless steel tubing for fluid transport.
- EN 10216-5 — European standard for non-alloy and alloy steel tubes for heat exchange equipment and general mechanical uses.
- MILL TEST CERTIFICATE (MTC) — Full material traceability documentation provided with each shipment, including chemical analysis, mechanical test results, and heat treatment records.
Unique Selling Points
- Specialized HVAC Anti-Freeze Engineering: Designed specifically for preheating coil applications with proven anti-freeze control performance, reducing system downtime and maintenance costs.
- Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional durability in humid, corrosive, and chemically aggressive HVAC environments, significantly outperforming copper or carbon steel alternatives.
- Precision Coil Winding: CNC-controlled winding ensures uniform geometry, consistent heat transfer surface area, and reliable hydraulic performance across the entire coil assembly.
- Wide Operating Temperature Range: Capable of functioning reliably from −40°C to +350°C, accommodating extreme thermal cycling conditions common in HVAC defrost and preheating cycles.
- Customizable Configurations: Flexible specifications for diameter, wall thickness, coil winding geometry, and connection methods to meet diverse system design requirements.
- Full Traceability & Compliance: Comprehensive quality documentation and adherence to international standards (ASTM, GB/T, EN) ensure regulatory compliance and supply chain transparency.