Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Grade
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1230) is a precision-engineered tubular product designed for integration into Fan Coil Units (FCUs) and other HVAC (Heating, Ventilation, and Air Conditioning) systems. This product category falls under the broader classification of literature-study and technical-reference materials, encompassing comprehensive design, fabrication, and installation guidelines for coil tube assemblies used in commercial and industrial thermal exchange applications.
The coil tube serves as the primary heat exchanger element within fan coil units, where working fluids (water, glycol solutions, or refrigerants) circulate through tightly wound stainless steel tubing to facilitate efficient heat transfer between the fluid medium and ambient air. The product knowledge base associated with this coil tube addresses critical engineering considerations in fan coil unit design, construction, and commissioning, drawing upon extensive metallurgical and thermal-hydraulic expertise.
Material & Properties
Wenzhou Jixing Metal Materials Co., Ltd. employs high-grade austenitic stainless steels conforming to international standards for the manufacture of coil tubes. The primary material grades utilized include:
- AISI 304 (UNS S30400): The standard austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Suitable for general-purpose HVAC applications where chloride exposure is minimal.
- AISI 316L (UNS S31603): Enhanced austenitic stainless steel with molybdenum (Mo) addition (2.0–2.5%) providing superior resistance to pitting and crevice corrosion, ideal for applications involving chlorinated water or marine environments.
Key Metallurgical Properties:
- Operating Temperature Range: −196 °C to +870 °C (continuous service)
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C (AISI 304)
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C (AISI 304, 20–100 °C)
- Corrosion Resistance: Excellent resistance to atmospheric, acidic, and alkaline environments
- Mechanical Strength: Yield strength ≥ 205 MPa; Ultimate tensile strength ≥ 515 MPa (annealed condition)
- Hygienic Surface: Passivated finish with surface roughness Ra ≤ 0.8 μm
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm, 8.00 mm, 9.53 mm, 12.70 mm (custom available) | ASTM A269 / ASTM B462 |
| Tube Wall Thickness | 0.50 mm – 1.50 mm | ASME B36.19M |
| Coil Pitch (Center-to-Center Spacing) | 10 mm – 25 mm (configurable) | Manufacturer Specification |
| Tube Rows | 1 to 6 rows (standard); up to 10 rows (special order) | ASHRAE Handbook — HVAC Systems and Equipment |
| Coil Length (Active Heat Transfer Zone) | 300 mm – 1,500 mm | Manufacturer Specification |
| Material Grade | AISI 304 / AISI 316L | ASTM A269; ASTM B462 |
| Surface Finish | Bright annealed / Pickled and passivated | ASTM A478 |
| Pressure Rating | Up to 1.6 MPa (standard); 2.5 MPa (reinforced) | EN 12163 / ISO 4413 |
| Connection Type | Flanged, threaded (BSPP/NPT), or brazed | ISO 7-1 / ASME B1.20.1 |
| Maximum Operating Fluid Temperature | 120 °C (hot water); −20 °C (chilled water/glycol) | ASHRAE 15 / EN 14511 |
| Refrigerant Compatibility | R-410A, R-32, R-22, R-407C | ISO 817 |
| Winding Direction | Left-hand (LH) or Right-hand (RH) helical coil | Manufacturer Specification |
Manufacturing Process
The production of high-quality stainless steel coil tubes follows a rigorous multi-stage manufacturing process:
- Material Selection and Incoming Inspection: Raw stainless steel bar stock or seamless tubing is procured from certified mills. Each batch undergoes spectroscopic analysis (PMI — Positive Material Identification), mechanical testing, and visual inspection to verify compliance with ASTM A269 or ASTM B462 requirements.
- Coil Winding (Helical Bending): The straight tubing is fed through precision-guided bending dies using CNC-controlled (Computer Numerical Control) coil winding machines. The winding parameters — pitch, helix angle, and coil diameter — are programmatically controlled to ensure dimensional accuracy within ±0.5 mm tolerance. The bending process is executed at ambient temperature to preserve the austenitic microstructure and avoid work-hardening-induced stress concentrations.
- Welding and Brazing: Inlet and outlet headers are joined to the coil ends using TIG (Tungsten Inert Gas) welding with argon shielding (minimum 99.99% purity) or high-temperature copper-phosphorus brazing (B-Cu-P series filler metals per AWS C3.3). Welds are inspected for penetration, porosity, and undercut.
- Heat Treatment (if applicable): For applications requiring stress relief, the coil assembly may undergo solution annealing at 1,050–1,150 °C followed by rapid air or water quenching, ensuring a fully recrystallized, carbide-free microstructure.
- Pickling and Passivation: The welded assembly is subjected to acid pickling (mixed HNO₃/HF solution) to remove heat-affected discoloration and oxide scales, followed by passivation with 20–30% HNO₃ solution to form a stable chromium oxide (Cr₂O₃) protective film. This process is critical for ensuring long-term corrosion resistance, particularly at weld zones.
- Pressure Testing: Each coil tube undergoes hydrostatic pressure testing at 1.5× the maximum design pressure (minimum 2.4 MPa) for a dwell time of no less than 30 minutes, with zero allowable leakage per ISO 5208 standards.
- Final Inspection and Certification: Dimensional verification (using laser measuring systems), surface quality assessment, and material traceability documentation are compiled into a complete quality dossier for each production batch.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. finds extensive application across multiple sectors:
- Commercial HVAC Systems: Fan coil units installed in office buildings, hotels, hospitals, and shopping centers for precise temperature and humidity control.
- Industrial Process Cooling/Heating: Integration into process air handlers, drying chambers, and thermal conditioning systems in manufacturing facilities.
- Food and Pharmaceutical Industry: Sanitary-grade coil tubes (AISI 316L, electropolished) for clean-room air handling, pharmaceutical drying, and food processing temperature control where hygienic standards (FDA 21 CFR Part 117, EHEDG) are mandated.
- Marine and Offshore Applications: Corrosion-resistant coil tubes for HVAC systems aboard vessels, offshore platforms, and coastal installations where chloride-induced pitting corrosion is a primary concern.
- Renewable Energy Systems: Heat recovery units in geothermal and solar thermal systems requiring durable, high-cycle-life heat exchanger elements.
- Data Centers: Precision cooling coil tubes for server room thermal management where continuous operation and minimal maintenance intervals are required.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that all coil tube products meet or exceed international standards:
- ISO 9001:2015: Quality Management System certification demonstrating systematic process control and continuous improvement.
- ISO 14001:2015: Environmental Management System certification for sustainable manufacturing practices.
- ISO 45001:2018: Occupational Health and Safety Management System certification.
- EN 10204 3.1: Material test certificates (MTC) provided with each shipment, issued by an authorized third-party inspector.
- CE Marking: Conformity with European directives for pressure equipment (PED 2014/68/EU) where applicable.
- ASME "S" Stamp: Sectional fabrication certification for pressure-containing coil assemblies.
- NSF/ANSI 61: Drinking water system components certification for applications involving potable water circuits.
Unique Selling Points and Technical Considerations
The coil tube product from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself through several critical technical advantages, as highlighted in the design and construction literature associated with this product category:
- Superior Corrosion Fatigue Resistance: The austenitic stainless steel construction eliminates the risk of intergranular corrosion and stress corrosion cracking (SCC) that commonly affects carbon steel alternatives in humid or chlorinated environments, significantly extending service life beyond 20 years under normal operating conditions.
- Precision Winding Tolerances: CNC-controlled helical winding ensures uniform coil pitch and consistent flow distribution across all tube rows, minimizing bypass flow and maximizing heat transfer efficiency (NTU — Number of Transfer Units — optimization).
- Design-Construction Integration Knowledge: The associated technical literature addresses critical installation considerations including proper condensate drainage slopes (minimum 1:100 gradient), air elimination provisions, thermal expansion accommodation, and noise/vibration isolation — all of which directly influence system performance and longevity.
- Full Traceability: Each coil tube is accompanied by complete material traceability documentation, including mill certificates, heat treatment records, welding procedure specifications (WPS), and non-destructive testing (NDT) reports.
- Custom Engineering Support: Wenzhou Jixing Metal Materials Co., Ltd. provides bespoke coil design services, including CFD (Computational Fluid Dynamics) simulation for thermal performance optimization, custom pitch/row configurations, and special alloy specifications tailored to specific application requirements.
Note on Design and Construction: The technical literature associated with this product (Product No. 1230) emphasizes several critical points for successful fan coil unit implementation: (1) proper matching of coil capacity to system design load, accounting for altitude and ambient condition variations; (2) adequate air-side filtration to prevent fouling of the coil tube surfaces; (3) correct integration of condensate management systems to prevent microbial growth and structural damage; (4) provision of thermal expansion loops or flexible connections to accommodate differential thermal expansion between the coil tube and connecting piping; and (5) commissioning protocols including balanced air/water flow verification and performance testing against manufacturer-rated capacity curves.
Product Classification: Literature Study / Technical Reference | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product No.: 1230 | Grade: AISI 304 / AISI 316L | Application: Fan Coil Unit Heat Exchanger