Stainless Steel Coil Tube — Fan Coil Water Flow Regulation Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubing product designed specifically for applications in hydronic heating, ventilation, and air conditioning (HVAC) systems. This product category encompasses seamlessly formed stainless steel tubes that are coiled into compact, space-efficient configurations optimized for integration into fan coil units (FCUs), heat exchangers, and liquid-to-liquid thermal transfer systems.
Drawing upon advanced methodologies for water flow rate regulation in fan coil systems, this coil tube product line addresses critical engineering challenges including laminar-to-turbulent flow transition management, pressure drop optimization, and thermal efficiency maximization. The coiled geometry provides an extended heat transfer surface area within a confined footprint, making it ideal for compact HVAC terminal units, industrial process cooling loops, and residential radiant systems.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, mechanical integrity, and thermal conductivity characteristics. Primary material grades include:
- SUS304 (UNS S30400 / 1.4301) — General-purpose grade with excellent formability and resistance to atmospheric and mild chemical corrosion.
- SUS316L (UNS S31603 / 1.4404) — Enhanced molybdenum content provides superior resistance to chloride-induced pitting and crevice corrosion.
- SUS321 (UNS S32100 / 1.4541) — Titanium-stabilized grade suitable for elevated-temperature applications exceeding 400 °C.
Key material properties:
- Corrosion Resistance: Passive chromium oxide film (Cr₂O₃) provides self-healing protection against oxidation in humid and mildly aggressive environments.
- Mechanical Strength: Yield strength ranging from 205 MPa (annealed) to 520 MPa (cold-worked), ensuring dimensional stability under cyclic thermal loading.
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20 °C, providing efficient heat transfer between the tube wall and the working fluid.
- Operating Temperature Range: −196 °C to +870 °C, accommodating cryogenic to high-temperature industrial processes.
- Hygienic Surface Finish: Available in electropolished (Ra ≤ 0.25 µm) or mechanically polished finishes for sanitary and pharmaceutical applications.
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6 mm – 25 mm (custom sizes available) | ASTM A269 / GB/T 12771 |
| Wall Thickness | 0.3 mm – 1.5 mm | ASTM A269 / EN 10217 |
| Coil Diameter | 150 mm – 600 mm (configurable) | — |
| Tube Length (Uncoiled) | 3 m – 50 m (or continuous coil) | — |
| Material Grade | SUS304 / SUS316L / SUS321 | ASTM A270 / EN 10088 |
| Surface Finish | Mill finish / Electropolished (Ra ≤ 0.25 µm) / Mirror polish | ASTM A269 |
| Connection Type | Welded / Flanged / Compression fitting / Brazed | ASME B31.9 |
| Maximum Working Pressure | 1.6 MPa – 6.3 MPa (pressure-tested) | ASME B31.3 |
| Water Flow Rate Range | 0.5 L/min – 12 L/min (system-dependent) | — |
| Pressure Drop (ΔP) | ≤ 50 kPa at rated flow velocity (optimized coil geometry) | — |
| Heat Transfer Coefficient | 2,000 – 5,500 W/(m²·K) (water-to-air, depending on configuration) | — |
| Service Life | ≥ 25 years (under normal operating conditions) | — |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Material Preparation: Cold-rolled stainless steel strip (coil) is inspected for surface defects, compositional conformity (spectrometric analysis), and mechanical properties. Incoming material is certified per ASTM A270 or EN 10088.
- Forming: The strip is fed through a series of progressively reducing rolls in a cold-forming (seamless tube making) process. This produces a seamless tube with uniform wall thickness and no weld seam, eliminating potential leakage paths.
- Heat Treatment (Annealing): Formed tubes are annealed at 1,050–1,100 °C followed by controlled cooling to restore austenitic microstructure, relieve cold-work stresses, and achieve desired mechanical properties.
- Pickling & Passivation: Tubes are subjected to acid pickling (nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation to establish a stable chromium oxide passive film.
- Coiling: The straight tube is precisely coiled using computer-controlled winding equipment. Coil diameter, pitch, and layer count are controlled to optimize thermal performance and minimize pressure drop. The coiling process is designed to avoid excessive bending strain that could induce work hardening or micro-cracking.
- Flow Regulation Optimization: The coil geometry is engineered to manage water flow distribution uniformly across all turns. Internal flow channel design accounts for the centrifugal effects in curved sections, ensuring balanced hydraulic resistance and preventing flow maldistribution — a critical consideration in fan coil water flow rate regulation.
- End Preparation & Connection: Tube ends are deburred, chamfered, and prepared for welding, brazing, or mechanical connection per the specified application requirements.
- Non-Destructive Testing (NDT): All coils undergo 100% eddy current inspection for internal and external defects, supplemented by hydrostatic pressure testing (typically 1.5× working pressure) to verify leak-tightness.
- Final Inspection & Packaging: Dimensional verification, surface finish measurement, and chemical composition re-confirmation are performed. Products are packaged in protective wrapping with moisture-absorbing desiccants.
Applications
The stainless steel coil tube is deployed across a broad spectrum of industries where reliable heat transfer, corrosion resistance, and compact design are paramount:
- HVAC Fan Coil Units (FCUs): Primary application — the coil tube serves as the water-side heat exchanger in air handling units, providing heating and cooling of indoor air streams. The optimized coil geometry ensures uniform water flow distribution, directly supporting effective water flow rate regulation and thermal performance.
- Industrial Process Cooling: Used in chemical processing, pharmaceutical manufacturing, and food processing plants for heat exchange in process fluid loops.
- Residential & Commercial Radiant Systems: Integrated into underfloor heating circuits and wall-mounted radiators for efficient low-temperature hydronic heating.
- Refrigeration & Chiller Systems: Employed as evaporator and condenser coils in commercial refrigeration units and industrial chillers.
- Marine & Offshore Systems: SUS316L grade coil tubes resist seawater corrosion in marine HVAC and cooling applications.
- Automotive Thermal Management: Used in vehicle air conditioning condenser coils and battery thermal management systems for electric vehicles.
- Medical & Laboratory Equipment: Electropolished coil tubes in cryogenic systems, medical gas delivery, and laboratory heat exchangers.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity with international standards:
- ISO 9001:2015 — Quality Management System certification covering design, manufacturing, and post-sale services.
- ISO 14001:2015 — Environmental Management System ensuring sustainable manufacturing practices and waste minimization.
- EN 10204 3.1 — Third-party material certification providing independent verification of chemical composition and mechanical properties.
- ASME B31.9 — Compliance with standards for refrigeration piping systems.
- CE Marking — Conformity with European directives for pressure equipment (PED 2014/68/EU).
- ASTM A269 / A270 — Product conformity with American standards for wrought austenitic stainless steel tubing.
- GB/T 12771 — Compliance with Chinese national standards for welded and seamless stainless steel tubes.
- Hydrostatic Testing — 100% pressure testing at 1.5× rated working pressure with documented test records for each production batch.
- Eddy Current Testing (ECT) — Automated inline inspection for 100% defect detection coverage on all manufactured coils.
Unique Selling Points
- Engineered Flow Distribution: The coil geometry is specifically optimized for uniform water flow rate regulation, addressing the challenge of flow maldistribution in multi-pass heat exchangers — a key insight derived from advanced fan coil hydraulic analysis methodologies.
- Seamless Construction: Eliminates weld-induced corrosion initiation sites and provides superior pressure containment compared to welded alternatives.
- Full Material Traceability: Every coil is traceable to its mill heat number with complete documentation of composition, mechanical properties, and processing history.
- Customizable Configurations: Flexible options for coil diameter, pitch, tube OD/wall thickness, material grade, and surface finish to meet application-specific thermal and hydraulic requirements.
- Extended Service Life: The combination of corrosion-resistant stainless steel and optimized hydraulic design ensures reliable operation exceeding 25 years without performance degradation.