Stainless Steel Coil Tube for Fan Coil Unit Room Air Conditioners
1. Product Overview
The stainless steel coil tube (盘管Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubing product specifically designed for integration into fan coil unit room air conditioners (风机盘管房间空调器). These coil tubes serve as the core heat exchange elements within the air conditioning system, facilitating efficient thermal transfer between the circulating refrigerant and the ambient air. The product is developed in strict compliance with the technical standards C34A003, C34A004, and D16A006, which govern the design, performance, and safety requirements for fan coil unit room air conditioning systems.
Coil tubes in fan coil applications are subjected to continuous cyclic thermal loading, pressure fluctuations, and potential exposure to condensate and moisture. Consequently, the material selection, dimensional accuracy, and surface integrity of the coil tube are critical determinants of the overall system reliability, energy efficiency, and service life.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade stainless steel (奥氏体不锈钢, Austenitic Stainless Steel), typically conforming to ASTM A269 (Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Piping) and ASTM A312 (Standard Specification for Seamless and Welded Austenitic Stainless Steel Tube for High-Temperature Service). Commonly specified grades include:
- AISI 304 / 06Cr19Ni10 — General-purpose austenitic grade offering excellent corrosion resistance and formability
- AISI 316L / 022Cr17Ni12Mo2 — Enhanced grade with molybdenum addition for superior resistance to chloride-induced pitting and crevice corrosion
- AISI 321 / 06Cr18Ni11Ti — Titanium-stabilized grade providing improved resistance to intergranular corrosion at elevated temperatures
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa | ASTM A269 / EN 10217 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ASTM A269 / EN 10217 |
| Elongation (延伸率) | ≥ 40% | ASTM A269 |
| Hardness (硬度) | ≤ 92 HRB (Brinell) | ASTM A269 |
| Impact Energy (冲击韧性) | ≥ 200 J at 20°C | ASTM E23 |
| Thermal Conductivity (导热系数) | 14–16 W/(m·K) | ASTM E153 |
| Corrosion Resistance (耐腐蚀性) | PASS — 96h Salt Spray Test | ASTM B117 |
2.3 Surface Treatment
The exterior surface of the coil tube may undergo electropolishing (电解抛光) or passivation treatment (钝化处理) to achieve a surface roughness of Ra ≤ 0.4 μm, enhancing both corrosion resistance and heat transfer efficiency. The interior surface is maintained in a clean, oxide-free condition to minimize fluid flow resistance and prevent fouling.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管Coiltube) |
| Item Number | 1709 |
| Applicable Standards | C34A003, C34A004, D16A006 |
| Outer Diameter (外径) | 6.0 mm / 6.35 mm / 8.0 mm / 9.52 mm / 10.0 mm (customizable) |
| Wall Thickness (壁厚) | 0.40 mm – 1.20 mm |
| Coil Pitch (盘管间距) | 12 mm – 25 mm (adjustable per application) |
| Coil Diameter (盘管直径) | 60 mm – 120 mm |
| Coil Length (盘管长度) | Up to 3,000 mm per assembly |
| Operating Pressure (工作压力) | ≤ 1.6 MPa (refrigerant side) |
| Operating Temperature Range (工作温度范围) | −40°C to +150°C |
| Winding Method (成型方式) | Hydraulic Coiling / Cold-Formed Coil Winding |
| Joining Method (连接方式) | Resistance Welding / TIG Welding (GTAW) / Flare Connection |
| Surface Finish (表面光洁度) | Ra ≤ 0.4 μm (electropolished) |
| Heat Transfer Efficiency (换热效率) | ≥ 92% (design condition) |
| Service Life (设计寿命) | ≥ 15 years under normal operating conditions |
4. Manufacturing Process
4.1 Raw Material Selection & Inspection
Stainless steel wire rod or seamless tube blanks are procured from certified mills and subjected to incoming quality inspection, including chemical composition analysis (光谱分析), mechanical property verification, and surface defect examination. Only material batches meeting the specified grade requirements (e.g., ASTM A269 Type 304/316L) are approved for production.
4.2 Precision Forming & Coiling
The forming process involves several sequential stages:
- Deburring & Cleaning (去毛刺与清洗) — Raw tubing ends are deburred and ultrasonically cleaned to remove oxide scale and contaminants.
- Dimensional Calibration (尺寸校准) — Outer diameter and wall thickness are verified using optical comparators and ultrasonic thickness gauges to ensure compliance within ±0.05 mm tolerance.
- Hydraulic Coiling / Cold Winding (液压盘绕成型) — The straight tube is wound into the specified coil geometry using precision hydraulic or mechanical coiling machines. The winding parameters (pitch, diameter, number of turns) are programmed according to the design specifications for each fan coil unit model.
- Springback Compensation (回弹补偿) — Algorithmic compensation is applied during coiling to account for elastic springback, ensuring the final coil geometry meets dimensional requirements.
4.3 Joining & Sealing
Tube-to-tube and tube-to-header joints are formed using one of the following methods:
- TIG Welding (GTAW) (钨极惰性气体保护焊) — Used for high-integrity joints requiring full penetration and leak-tight seals. Argon shielding gas is applied on both the interior and exterior of the weld zone.
- Resistance Welding (电阻焊) — Employed for butt joints where rapid, repeatable production is required.
- Flare Connection (喇叭口连接) — Used at terminal ends for field assembly and maintenance access.
4.4 Surface Treatment & Finishing
Post-forming surface treatments include:
- Passivation (钝化) — Immersion in a nitric acid or citric acid solution to remove free iron and promote the formation of a protective chromium oxide layer.
- Electropolishing (电解抛光) — Anodic dissolution of surface irregularities to achieve a mirror-like finish with Ra ≤ 0.4 μm, significantly reducing fluid friction and enhancing heat transfer.
- Corrosion Inhibitor Coating (防腐涂层) — Application of a thin protective coating on the exterior surface for additional long-term corrosion protection.
4.5 Final Testing & Quality Control
Each coil tube assembly undergoes rigorous final inspection before shipment:
- Dimensional Inspection — Verification of coil diameter, pitch, overall length, and tube geometry using coordinate measuring machines (CMM) or laser scanners.
- Pressure Testing (压力测试) — Hydrostatic or pneumatic pressure test at 1.5× the maximum operating pressure to verify leak-tight integrity.
- Leak Detection (泄漏检测) — Helium leak testing or soap-bubble inspection of all joints.
- Visual & NDT Inspection (目视检测与无损检测) — Visual examination of welds and surfaces; optional dye penetrant testing (PT) or eddy current testing (ECT) for weld integrity.
5. Applications
The stainless steel coil tube is primarily designed for the following application domains:
5.1 Fan Coil Unit Room Air Conditioners (风机盘管房间空调器)
As the primary heat exchange component within fan coil units, the coil tube directly determines the system's cooling and heating capacity. The high thermal conductivity and corrosion resistance of stainless steel ensure consistent performance across both cooling (制冷) and heating (制热) modes, even in environments with high humidity or mild corrosive exposure.
5.2 Commercial HVAC Systems (商用暖通空调系统)
Used in large-scale commercial buildings, hotels, hospitals, and office complexes where fan coil units are deployed for zoned temperature control and high indoor air quality (IAQ) management.
5.3 Industrial Process Cooling (工业过程冷却)
Applicable in industrial settings requiring precise temperature regulation with resistance to chemical exposure and aggressive environmental conditions.
5.4 Cleanroom & Pharmaceutical Applications (洁净室与制药应用)
The electropolished surface finish and hygienic design of the coil tube make it suitable for cleanroom air conditioning systems in pharmaceutical manufacturing, biotechnology, and food processing facilities.
6. Quality Certifications
The product and manufacturing process at Wenzhou Jixing Metal Materials Co., Ltd comply with the following international and national quality standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and continuous improvement |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System certification |
| C34A003 | Technical standard for fan coil unit room air conditioners — design and performance requirements |
| C34A004 | Technical standard for fan coil unit room air conditioners — safety and environmental requirements |
| D16A006 | Technical standard for fan coil unit room air conditioners — testing and acceptance criteria |
| ASTM A269 / A312 | Material specification for seamless and welded austenitic stainless steel tubing |
| EN 10217 | European standard for stainless steel tubes for pressure purposes |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for general engineering |
| GB/T 14975 | Chinese national standard for cold-rolled stainless steel tubes for general engineering |
7. Unique Selling Points
Exceptional Corrosion Resistance: The use of high-grade austenitic stainless steel (AISI 304/316L) provides outstanding resistance to pitting, crevice, and intergranular corrosion, ensuring a design service life of ≥15 years even in humid or mildly corrosive environments.
Superior Heat Transfer Efficiency: The electropolished interior surface (Ra ≤ 0.4 μm) minimizes fluid flow resistance and maximizes convective heat transfer, achieving thermal efficiency ≥92% under design conditions.
Precision Dimensional Control: Advanced hydraulic coiling technology with algorithmic springback compensation ensures coil geometry accuracy within ±0.05 mm, guaranteeing optimal fit within fan coil unit housings and maximizing air-side heat exchange area.
Comprehensive Standard Compliance: Full alignment with C34A0