Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd
Product Code: 1685 | Category: Literature & Technical Reference | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product formed into a continuous spiral coil configuration, manufactured from high-grade austenitic and ferritic stainless steel grades. This product is specifically designed for integration into fan coil unit (FCU) systems, HVAC (Heating, Ventilation, and Air Conditioning) applications, and industrial heat exchange assemblies where corrosion resistance, thermal efficiency, and mechanical integrity are paramount.
Wenzhou Jixing Metal Materials Co., Ltd leverages advanced cold-forming and coil-winding technologies to produce coil tubes with tight dimensional tolerances, consistent wall thickness, and superior surface finish. The coil geometry maximizes surface area within a compact envelope, making it an ideal solution for air-handling units, condensers, evaporators, and refrigeration circuits.
2. Material & Properties
2.1 Base Materials
- Austenitic Grades: SUS304 (UNS S30400), SUS316 (UNS S31600), SUS321 (UNS S32100) — offering excellent corrosion resistance, weldability, and formability at both ambient and elevated temperatures.
- Ferritic Grades: SUS430 (UNS S43000), SUS409 (UNS S40900) — providing cost-effective solutions with adequate corrosion performance for less aggressive environments.
- Duplex Grades: SUS2205 (UNS S31803) — delivering high strength (yield strength up to 450 MPa) and exceptional resistance to chloride-induced stress corrosion cracking (SCC).
2.2 Key Mechanical and Physical Properties
| Property | SUS304 | SUS316 | SUS2205 (Duplex) |
|---|---|---|---|
| Yield Strength (MPa) | ≥205 | ≥170 | ≥450 |
| Tensile Strength (MPa) | 515–720 | 485–720 | 550–800 |
| Elongation (%) | ≥40 | ≥40 | ≥25 |
| Density (g/cm³) | 7.93 | 8.00 | 7.80 |
| Thermal Conductivity (W/m·K at 100°C) | 16.3 | 14.6 | 11.0 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −50 to +300 |
| Corrosion Resistance (ASTM G48) | Good | Excellent | Outstanding |
2.3 Surface Finish Options
- 2B Finish: Standard cold-rolled surface with moderate luster; suitable for general HVAC applications.
- No. 4 Brushed Finish: Unidirectional grain pattern; enhanced aesthetic appeal for visible installations.
- Mirror / 8K Finish: High-polish reflective surface; used in food-grade and pharmaceutical applications.
- Pickled & Passivated: Removal of mill scale followed by chemical passivation to restore the protective chromium oxide layer (Cr₂O₃).
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (1/4" – 2") |
| Wall Thickness | 0.4 mm – 3.0 mm (tolerance ±10%) |
| Coil Pitch (Center-to-Center) | 8 mm – 30 mm (customizable) |
| Coil Diameter (Overall) | 50 mm – 600 mm |
| Number of Turns | 4 – 500 turns |
| Coil Length (Unwound Equivalent) | Up to 12,000 mm per coil assembly |
| End Connection Types | Flared, Threaded (GAS/NPT), Weld Stub, Grooved |
| Dimensional Tolerance (OD) | ±0.15 mm |
| Dimensional Tolerance (Pitch) | ±0.5 mm |
| Applicable Standards | ASTM A269 / A270, ASME B36.19M, EN 10216-5, JIS G3459 |
| Maximum Design Pressure | Up to 4.0 MPa (grade-dependent) |
| Maximum Operating Temperature | Up to 870°C (austenitic grades) |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel seamless or welded tubes are verified against ASTM/EN standards for chemical composition (spectrometric analysis), mechanical properties (tensile testing), and surface integrity (visual + eddy current testing).
- Tube Straightening & Cutting: Tubes are precision-straightened using hydraulic straighteners and cut to required lengths with cold-saw machines to achieve perpendicular end faces (squareness tolerance ≤0.5°).
- End Preparation: End faces are deburred, chamfered, and cleaned to remove oxide scale and machining residues, ensuring optimal weldability and seal integrity.
- Coil Forming: Tubes are wound around a mandrel using CNC-controlled coiling machines. The winding parameters (pitch, tension, number of turns) are programmed to ensure uniformity and dimensional accuracy. Cold-forming at room temperature preserves the metallurgical properties of the stainless steel without requiring post-forming annealing.
- U-Turn / Return Bending: Where applicable, U-bends are formed at coil terminals using hydraulic bending tools with internal mandrels to prevent wall thinning and ovality, maintaining a minimum bend radius of 1.5× OD.
- Welding & Assembly: Header connections, stub ends, and U-bends are joined using TIG (Tungsten Inert Gas) welding under argon shielding to prevent oxidation. Weld seams are radiographic-tested (RT) or dye-penetrant-tested (PT) for defect detection.
- Pickling & Passivation: The assembled coil tube undergoes chemical pickling (HNO₃/HF acid bath) to dissolve weld discoloration and mill scale, followed by passivation to re-establish the passive chromium oxide film (minimum 10% Cr₂O₃ layer thickness).
- Hydrostatic Pressure Testing: Each coil tube assembly is pressure-tested at 1.5× the maximum design pressure (typically 1.5× 4.0 MPa = 6.0 MPa) with water, held for a minimum of 60 seconds to verify leak-tightness.
- Final Inspection & Packaging: Finished products undergo dimensional verification (calipers, micrometers, coordinate measuring machines), visual surface inspection, and are packaged with protective end caps, moisture-absorbing desiccants, and corrosion-inhibiting VCI (Vapor Corrosion Inhibitor) wraps.
5. Applications
5.1 Fan Coil Unit (FCU) Systems
In fan coil unit air conditioning systems, the stainless steel coil tube serves as the primary heat exchanger element. The coil configuration ensures maximum heat transfer surface area within the compact FCU housing. The selection of coil tube material and geometry directly influences:
- Cooling/Heating Capacity: Higher surface area-to-volume ratio improves thermal efficiency.
- Pressure Drop: Optimal pitch and tube diameter minimize fluid-side pressure drop, reducing fan energy consumption.
- Condensation Management: Smooth inner surfaces reduce scale formation and maintain long-term heat transfer performance.
5.2 Additional Applications
- Refrigeration & Air Conditioning: Evaporator and condenser coils in commercial and industrial refrigeration systems.
- Industrial Heat Exchangers: Shell-and-tube, plate-fin, and air-cooled heat exchangers in chemical processing, petrochemical, and power generation industries.
- Food & Beverage Processing: Heat exchange coils in pasteurization, sterilization, and CIP (Clean-in-Place) systems where hygiene and corrosion resistance are critical.
- Pharmaceutical & Biotechnology: Sterilizable heat transfer coils in bioreactors, fermenters, and cleanroom HVAC systems.
- Marine & Offshore: Seawater-cooled heat exchangers where chloride resistance (SUS316 or duplex grades) is essential.
- Automotive & Transportation: Intercoolers, oil coolers, and thermal management coils in high-performance vehicles.
6. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control. |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices. |
| ISO 3834 (Part 2) | Quality requirements for fusion welding of metallic materials — applicable to TIG welding processes used in coil tube assembly. |
| EN 10204 Type 3.1 | Inspection certificate certifying conformity of material with specified standards, issued by a qualified third-party inspector. |
| NACE MR0175 / ISO 15156 | Materials for use in H₂S-containing environments in oil and gas industry — applicable to SUS316 and duplex grades. |
| NSF/ANSI 61 | Health effects of drinking-water system components — applicable to food-grade and potable water applications. |
| CE Marking (EU) | Conformity with European Union directives for machinery and pressure equipment (PED 2014/68/EU). |
| ASME "U" Stamp | American Society of Mechanical Engineers certification for pressure vessel and heat exchanger components. |
7. Unique Selling Points
- Precision Coil Geometry: CNC-controlled winding ensures pitch uniformity within ±0.5 mm, enabling predictable and repeatable thermal performance in FCU and heat exchanger applications.
- Material Versatility: Availability across austenitic, ferritic, and duplex stainless steel grades allows engineers to optimize the cost-performance-corrosion triangle for specific service conditions.
- Elimination of Post-Forming Annealing: Cold-forming process preserves the as-supplied mechanical properties of austenitic stainless steels (e.g., SUS304, SUS316), avoiding grain growth and sensitization associated with solution annealing.
- Integrated Quality Traceability: Each coil tube batch is traceable from raw material heat number through manufacturing process parameters to final inspection records, supporting full supply-chain accountability.
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd offers tailored coil tube configurations — including non-standard pitches, special end treatments, and custom tube counts — to meet project-specific design requirements in fan coil unit and heat exchanger engineering.
- Extended Service Life: Superior corrosion resistance of stainless steel coil tubes eliminates the need for internal coatings or sacrificial anodes, reducing lifecycle maintenance costs by an estimated 40–60% compared to carbon steel alternatives.
8. Technical Reference: Fan Coil Unit Design Considerations
The design of coil tubes for fan coil unit applications must address several critical engineering challenges:
- Heat Transfer Optimization: The coil tube OD, wall thickness, and pitch must be selected to balance heat transfer coefficient (U-value) against pressure drop, targeting a U-value of 80–120 W/m²·K for air-to-water FCU applications.
- Condensate Drainage: Coil tube surfaces must be oriented and configured to prevent condensate retention, which degrades heat transfer efficiency and promotes microbial growth. Surface finish (2B or better) and tube layout angles are critical design parameters.
- Freeze Protection: In cold-climate applications, coil tube configurations must allow complete drainage to prevent freeze damage. Minimum tube diameter of 6.35 mm (1/4") is recommended to limit residual water volume.
- Acoustic Performance: Coil tube geometry influences air-side flow patterns and noise generation. Smooth tube surfaces and optimized pitch reduce turbulence-induced noise by 3–5 dBA compared to rough-surface alternatives.
- Material Selection for FCU Environments: SUS304 is the baseline recommendation for standard indoor FCU applications. SUS316 is required where condensate pH is below 5.5 or where cleaning agents contain chlorides. SUS2205 duplex is recommended for coastal or industrial environments with elevated chloride exposure.
Technical documentation prepared for Wenzhou Jixing Metal Materials Co., Ltd — Product Code 1685. All specifications are subject to verification against applicable international standards and project-specific engineering requirements. Consult the manufacturer for grade-specific data sheets and application engineering support.