Stainless Steel Coil Tube (盘管 / Coil Tube) — Technical Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Code: No. 1222
Category: Literature-Based Technical Reference — HVAC & Thermal Management Systems
Reference Document: "Discussion on the Control of Fan Coil Unit Plus Fresh Air System" (风机盘管加新风系统的控制探讨)
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular component formed into helical or serpentine configurations, primarily designed for use in Fan Coil Unit (FCU) assemblies and Fresh Air Supply Systems within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) installations. As a critical heat-exchange medium, the coil tube facilitates efficient thermal transfer between the working fluid (water, refrigerant, or glycol solution) and the ambient air stream, thereby enabling precise temperature and humidity regulation within enclosed spaces.
Based on the technical study documented in "Discussion on the Control of Fan Coil Unit Plus Fresh Air System," the coil tube serves as the fundamental structural and functional element in the thermal loop. The study emphasizes that the geometric configuration, material integrity, and surface finish of the coil tube directly influence the overall thermal efficiency, pressure drop characteristics, and long-term operational reliability of the HVAC system. Wenzhou Jixing Metal Materials Co., Ltd. manufactures these coil tubes to meet the demanding performance criteria outlined in this control-system literature, ensuring compatibility with modern variable-speed drive (VSD) and direct digital control (DDC) architectures.
2. Material & Properties
2.1 Base Alloy Composition
The coil tubes are fabricated from austenitic stainless steel conforming to international standards. The primary grades utilized are:
- ASTM A213 TP304 / TP316 — Seamless stainless steel tubes for heat exchangers and heat-transfer equipment
- EN 10216-5 — Welded stainless steel tubes for pressure purposes
- GB/T 17898 — Chinese national standard for stainless steel tubes for heat exchangers
2.2 Mechanical Properties
| Property | TP304 Grade | TP316 Grade | Test Standard |
|---|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa | ≥ 515 MPa | ASTM A370 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ≥ 205 MPa | ASTM A370 |
| Elongation (延伸率) | ≥ 40% | ≥ 40% | ASTM A370 |
| Hardness (硬度, HV) | ≤ 200 | ≤ 200 | ASTM E92 |
| Corrosion Resistance (耐腐蚀性) | Good (oxidizing acids) | Excellent (chloride-containing environments) | ASTM A967 |
| Thermal Conductivity (导热系数) | 16.3 W/(m·K) at 20°C | 16.3 W/(m·K) at 20°C | — |
| Operating Temperature Range (工作温度范围) | −196°C to +870°C | −196°C to +870°C | — |
2.3 Chemical Composition (Typical)
| Element | TP304 (%) | TP316 (%) |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.08 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 | ≤ 1.0 |
| Sulfur (S) | ≤ 0.03 | ≤ 0.03 |
3. Specifications
| Parameter | Specification / Range | Notes |
|---|---|---|
| Outer Diameter (外径, OD) | 6.35 mm, 9.53 mm, 12.70 mm, 15.88 mm, 19.05 mm | Standard imperial sizes; custom OD available |
| Wall Thickness (壁厚) | 0.50 mm – 1.65 mm | Selected based on pressure rating and thermal duty |
| Coil Pitch (盘管节距) | 10 mm – 50 mm | Determined by heat exchanger design and airflow requirements |
| Coil Diameter (盘管直径) | 50 mm – 500 mm | Customizable per FCU unit dimensions |
| Tube Length per Coil (单圈管长) | 0.3 m – 3.0 m | Dependent on application thermal load |
| Surface Finish (表面光洁度) | Ra ≤ 0.8 μm (inner); Ra ≤ 1.6 μm (outer) | Reduced surface roughness minimizes fouling and pressure loss |
| Surface Treatment (表面处理) | Pickling & Passivation (酸洗钝化) | Per ASTM A967 / ASTM A380 |
| Pressure Rating (压力等级) | Up to 1.6 MPa (standard); up to 4.0 MPa (reinforced) | Hydrostatic test at 1.5× working pressure |
| End Connections (端部连接) | Sweat-brazed, flanged, or threaded | Compatible with copper, brass, and stainless steel fittings |
| Coating (涂层, optional) | Anti-corrosion lacquer or PTFE (聚四氟乙烯) coating | For aggressive environments or food-grade applications |
| Temperature Class (温度等级) | Cryogenic (−196°C) to High-Temperature (+870°C) | Full austenitic range |
| Standard Compliance (标准合规) | ASTM A213, EN 10216-5, GB/T 17898, JIS G3459 | Multinational standard alignment |
4. Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical integrity, and consistent thermal performance:
- Raw Material Procurement (原材料采购): Certified stainless steel round bars or seamless tube blanks are sourced from approved mills. Each batch undergoes spectrographic analysis (光谱分析) to verify chemical composition compliance with ASTM A213 or EN 10216-5 specifications.
- Hot Rolling or Cold Drawing (热轧或冷拔): The base tubes are produced via hot-rolling for larger diameters or cold-drawing for smaller, precision diameters. Cold drawing is preferred for coil tube applications as it yields superior dimensional tolerances (±0.05 mm) and improved surface finish.
- Heat Treatment (热处理): Solution annealing (固溶处理) is performed at 1050°C – 1150°C followed by rapid water quenching to achieve a fully austenitic microstructure, ensuring maximum ductility and corrosion resistance.
- Precision Coiling (精密盘绕): The annealed tubes are fed through CNC-controlled coiling machines that form the helical geometry to exact pitch, diameter, and turn-count specifications. The coiling process employs controlled die sets to prevent tube wall thinning, ovalization, or work-hardening.
- Welding & Brazing (焊接与钎焊): For multi-pass coil configurations, U-bends or header connections are formed and joined using orbital TIG welding (Tungsten Inert Gas, 钨极氩弧焊) or vacuum brazing. Weld joints are inspected via dye penetrant testing (PT, 渗透检测) or radiographic testing (RT, 射线检测).
- Pickling & Passivation (酸洗钝化): The finished coil assemblies undergo chemical cleaning to remove oxide scale, welding discoloration, and surface contaminants. A chromium-rich passive film is established to enhance corrosion resistance, in accordance with ASTM A967.
- Hydrostatic Pressure Testing (水压试验): Each coil tube assembly is subjected to a hydrostatic test at 1.5× the maximum working pressure for a minimum hold time of 5 minutes, with zero leakage tolerance.
- Dimensional Inspection & Quality Control (尺寸检验与质量控制): Final inspection includes verification of OD, wall thickness, coil pitch, overall length, and straightness using coordinate measuring machines (CMM) and ultrasonic thickness gauges.
5. Applications
The stainless steel coil tube, as specified and studied in the referenced literature on FCU and fresh air system control, finds extensive application across multiple industrial and commercial sectors:
- Fan Coil Units (风机盘管, FCU): The coil tube serves as the primary heat exchanger within FCU systems, where it transfers thermal energy between the circulating water (hot or chilled) and the air stream blown across the coil by an integrated fan. The study highlights that coil tube geometry directly impacts the system's capacity to maintain set-point temperatures under variable load conditions.
- Fresh Air Handling Systems (新风系统): In dedicated fresh air units, coil tubes are used for pre-cooling or pre-heating of outdoor air before it is introduced into the conditioned space, reducing the thermal load on the primary FCU.
- Commercial HVAC (商业暖通空调): Hotels, shopping malls, office buildings, hospitals, and educational institutions rely on coil tubes in their distributed air-handling systems for zoned climate control.
- Industrial Process Cooling & Heating (工业过程冷却与加热): Used in chemical processing, pharmaceutical manufacturing, food and beverage production, and electronics manufacturing for precise thermal management of process fluids.
- Refrigeration & Air Conditioning (制冷与空调): Coil tubes are integral components of evaporators and condensers in both central and split-type refrigeration systems.
- Automotive Thermal Management (汽车热管理): Stainless steel coil tubes are employed in automotive air conditioning condensers and intercoolers, where corrosion resistance and thermal cycling endurance are critical.
- Marine & Offshore (海洋与离岸工程): TP316-grade coil tubes are specified for marine HVAC systems and offshore platform climate control, where resistance to chloride-induced pitting corrosion is paramount.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification to assure international market access and customer confidence:
- ISO 9001:2015 — Quality Management System (质量管理体系)
- ISO 14001:2015 — Environmental Management System (环境管理体系)
- ISO 45001:2018 — Occupational Health and Safety Management System (职业健康安全管理体系)
- CE Marking — Conformity with European Union directives for pressure equipment and HVAC components
- ASTM International Compliance — Materials tested and certified per ASTM A213, A269, A967, and A380
- EN Standards Compliance — Conformance to EN 10216-5 and EN 10217-7 for stainless steel tubes