Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered seamless or welded stainless steel tubing supplied in continuous coil form, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product category is specifically designed for applications in HVAC (Heating, Ventilation, and Air Conditioning) systems, fresh air handling units, heat exchangers, refrigeration coils, and industrial fluid transport where resistance to corrosion, thermal cycling, and freeze-thaw conditions is critical.
Coiltube products are distinguished from straight-length tubing by their continuous coil configuration, which facilitates automated forming, cutting, and installation processes. The coil geometry enables efficient material utilization, reduced waste, and streamlined manufacturing workflows in downstream applications such as fin-and-tube heat exchanger fabrication.
A key area of technical focus for this product line is the anti-freeze performance of fresh air coil tubes — a critical engineering consideration in regions with cold climates. Research and development efforts have been directed toward optimizing coil tube wall thickness, material selection, and geometric parameters to mitigate the risks of ice formation, tube rupture, and thermal stress failure during low-temperature operation.
2. Material and Properties
Coiltube products are manufactured from a range of austenitic and duplex stainless steel grades, selected to meet specific environmental and mechanical requirements:
- Austenitic Grades: SUS304 (UNS S30400), SUS304L (UNS S30403), SUS316L (UNS S31603) — offering excellent corrosion resistance, formability, and weldability.
- Duplex Grades: SUS316Ti, SUS321 (UNS S32100) — providing enhanced resistance to pitting corrosion and stress corrosion cracking (SCC).
- Low-Carbon Variants: 304L and 316L grades contain reduced carbon content (≤0.03% C) to minimize intergranular corrosion during welding.
Key Mechanical Properties (Typical for SUS304 Grade):
- Tensile Strength (UTS): ≥ 520 MPa
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa
- Elongation: ≥ 40%
- Hardness: ≤ 92 HRB (annealed condition)
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Linear Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C
- Operating Temperature Range: −196°C to +870°C (vacuum); −196°C to +800°C (air)
Corrosion Resistance Characteristics:
- Excellent resistance to atmospheric corrosion, aqueous solutions, and food-grade environments.
- SUS316L grade provides superior resistance to chlorides and marine environments.
- Passive chromium oxide film (Cr₂O₃) provides self-healing surface protection.
3. Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A554 / ASTM A213 |
| Wall Thickness (WT) | 0.4 mm – 3.0 mm | JIS G3459 / GB/T 14976 |
| Coil Length (per coil) | 100 m – 500 m (customizable) | Manufacturer specification |
| Coil Inner Diameter (ID) | 300 mm – 600 mm | Manufacturer specification |
| Surface Finish | 2B, No. 4 (Brushed), BA (Bright Annealed), Mirror (8K) | ASTM A480 |
| Tolerance — OD | ±0.05 mm (precision grade); ±0.1 mm (standard grade) | ASTM A554 |
| Tolerance — WT | ±10% of nominal wall thickness | ASTM A554 |
| End Form | Plain cut, beveled, or tube-forming compatible | Per customer drawing |
| Heat Treatment | Solution annealed (1050°C – 1150°C), water quench | ASTM A213 |
| Applicable Grades | SUS304, SUS304L, SUS316L, SUS321, SUS316Ti | ASTM A213 / JIS G3459 |
| Packaging | Wooden pallet with moisture-proof wrapping; export-grade packaging available | ISO 4180 |
4. Manufacturing Process
The production of high-quality stainless steel coiltube follows a rigorously controlled multi-stage manufacturing sequence:
- Raw Material Procurement: Ingot or wire rod sourced from certified mills (e.g., Outokumpu, POSCO, Baosteel), with full chemical composition verification via spectrometric analysis.
- Wire Drawing / Seamless Forming: For small OD tubes (≤ 16 mm), cold-drawn seamless tubing is produced via rotary swaging or cross-rolling processes. For larger diameters, cold-rolled coil is formed into tubes using helical winding or longitudinal welding methods.
- Welding (for welded grades): TIG (Tungsten Inert Gas) welding is employed with continuous argon shielding to ensure a clean, oxidation-free weld seam. Weld bead width is controlled to ≤ 1.5 mm for optimal strength and appearance.
- Heat Treatment (Solution Annealing): Tubes are subjected to solution annealing at 1050°C – 1150°C followed by rapid water quenching. This dissolves carbides, restores full austenitic microstructure, and maximizes corrosion resistance.
- Pickling and Passivation: Post-annealing tubes undergo acid pickling (HNO₃ + HF blend) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide passive layer.
- Precision Sizing: Cold sizing passes through calibrated dies to achieve tight dimensional tolerances on OD and WT.
- Coiling: Finished tubes are coiled onto mandrels of specified inner diameter using automated coiling heads that control tension to prevent deformation, kinking, or ovality.
- Quality Inspection: Each coil undergoes dimensional verification (caliper, micrometer), visual inspection, hydrostatic pressure testing, and optional eddy current testing for weld integrity.
- Packaging and Storage: Coils are wrapped with moisture-barrier film, secured on wooden pallets, and labeled with batch traceability information.
5. Applications
The Coiltube product line from Wenzhou Jixing Metal Materials Co., Ltd serves a wide spectrum of industrial and commercial applications:
- HVAC Fresh Air Systems: Coil tubes are the primary heat exchange elements in fresh air handling units (AHUs). Anti-freeze design considerations include optimized tube spacing, enhanced wall thickness at bend points, and material selection for low-temperature ductility.
- Refrigeration and Air Conditioning Coils: Evaporator and condenser coil tubes for commercial refrigeration, split AC units, and chiller systems.
- Industrial Heat Exchangers: Plate-fin and shell-and-tube heat exchangers in chemical processing, pharmaceutical manufacturing, and food processing industries.
- Automotive Radiators and Condensers: Compact coil tubes for automotive HVAC systems and electric vehicle (EV) battery thermal management.
- Food and Beverage Processing: Hygienic-grade tubing for pasteurization, sterilization, and dairy processing equipment (3-A Sanitary standards compatible).
- Marine and Offshore Applications: Seawater cooling coils, desalination plant heat exchangers (SUS316L grade recommended).
- Medical Equipment: Sterilizable heat exchange coils for medical gas systems and cleanroom HVAC.
- Building Services: Radiator coil tubes, underfloor heating systems, and solar thermal collectors.
6. Anti-Freeze Engineering Considerations for Fresh Air Coil Tubes
A specialized technical domain associated with this product line addresses the anti-freeze measures for fresh air coil tubes, which is a critical safety and reliability concern in cold-climate installations:
- Material Selection: Austenitic stainless steels (SUS304/316L) maintain ductility at temperatures as low as −196°C, preventing brittle fracture during ice expansion within tube walls.
- Wall Thickness Optimization: Minimum wall thickness is calculated based on the internal hydraulic pressure generated by ice formation (approximately 100–200 MPa), ensuring the tube wall withstands freeze-induced hoop stress without rupture.
- Geometric Design: Tube-to-fin spacing, tube pitch, and row configuration are optimized to minimize airflow stagnation zones where ice accumulation is most likely.
- Anti-Freeze Control Integration: Coil tube systems are designed for compatibility with glycol-based antifreeze solutions (ethylene glycol or propylene glycol, 25–50% by volume), which depress the freezing point to −15°C to −35°C.
- Low-Flow Protection: Tube diameter and coil circuit configuration are engineered to maintain minimum fluid velocity thresholds that prevent localized freezing even at low ambient temperatures.
7. Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management and product certification programs:
- Quality Management System: ISO 9001:2015 certified
- Product Standards Compliance: ASTM A554 (Stainless Steel Seamless Tube for Heat Exchangers), ASTM A213 (Boiler, Heat Exchanger, and Condenser Tubes), JIS G3459 (Stainless Steel Tubes for General Use), GB/T 14976 (Chinese National Standard for Stainless Steel Seamless Tubes)
- Material Certifications: Mill Test Certificates (MTC) conforming to EN 10204 Type 3.1, providing full chemical composition and mechanical property data for each batch
- Non-Destructive Testing (NDT): Eddy current testing (ECT) for weld seam integrity; hydrostatic pressure testing per ASTM A530
- Industry-Specific Certifications: PED (Pressure Equipment Directive, EU) compliance for pressure-containing applications; ASME Section VIII Div. 1 stamping availability for pressure vessel applications
- Environmental Compliance: RoHS compliant; REACH registered; no restricted substances in material composition
- Food Safety: FDA 21 CFR compliant for food-contact applications; 3-A Sanitary Standards compatible for dairy and beverage processing
8. Unique Selling Points
- Precision Dimensional Control: ±0.05 mm OD tolerance ensures seamless integration into automated tube-bending and fin-stamping equipment, reducing downstream manufacturing rejects.
- Full Traceability: Every coil is batch-traceable to mill origin with complete chemical and mechanical certification documentation.
- Anti-Freeze Engineering Expertise: Proprietary design guidelines for fresh air coil tube systems in cold-climate environments, backed by thermal-hydraulic simulation and field validation.
- Custom Grade and Specification: Flexible customization of grade, dimensions, surface finish, and coil configuration to meet specific customer requirements.
- Cost-Efficient Coil Supply: Continuous coil format reduces material waste by up to 15% compared to straight-length tubing, offering significant cost advantages for high-volume coil manufacturing.
- Global Export Capability: Export-grade packaging and documentation compliant with international shipping standards; established supply chain serving markets in Asia, Europe, North America, and the Middle East.
Technical Note: When specifying Coiltube for fresh air handling applications in regions with winter temperatures below 0°C, it is strongly recommended to consult with Wenzhou Jixing Metal Materials Co., Ltd's engineering team regarding anti-freeze design parameters, including minimum wall thickness, coil geometry optimization, and glycol solution compatibility, to ensure system reliability and prevent costly coil failure events.