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 continuous-loop piping product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Jixing Metal). Unlike straight-segment stainless steel tubes that require field welding or mechanical joining, Coiltube is supplied as a long, continuous helical coil that can be cut to length on-site, thereby eliminating the need for on-site welding joints and significantly reducing the risk of contamination and leak points. This makes it particularly advantageous for applications in hygienic processing, heat exchange systems, and fan coil unit (FCU) assemblies used in densely populated commercial buildings where indoor air quality and humidity control are critical.
The product is designed to meet the rigorous demands of modern HVAC (Heating, Ventilation, and Air Conditioning) systems, food and beverage processing, pharmaceutical manufacturing, and chemical industries. The continuous coil form factor enables efficient heat transfer performance while minimizing the number of joints — a critical advantage for maintaining sanitary conditions and system reliability.
2. Material & Properties
2.1 Base Material Composition
The Coiltube is fabricated from high-grade austenitic stainless steel, conforming to the following international standards:
- AISI 304 / ASTM A213 TP304 — The standard grade for general-purpose applications, offering excellent corrosion resistance, formability, and weldability. Composition: 18–20% Cr (Chromium), 8–10.5% Ni (Nickel), ≤0.08% C (Carbon).
- AISI 316 / ASTM A213 TP316 — Enhanced grade with added Molybdenum (2.0–3.0% Mo) for superior resistance to pitting and crevice corrosion, suitable for aggressive chemical environments and coastal applications.
- AISI 316L / ASTM A213 TP316L — Low-carbon variant (≤0.03% C) of 316, ideal for applications requiring welding without risk of sensitization or intergranular corrosion.
- AISI 321 / ASTM A213 TP321 — Titanium-stabilized grade (5×C% Ti) for high-temperature service up to 870°C, providing excellent resistance to oxidation and thermal cycling.
2.2 Key Physical & Mechanical Properties
- Density: 7.93 g/cm³ (304/316); 7.95 g/cm³ (321)
- Thermal Conductivity: 16.3 W/(m·K) at 100°C (304); 14.6 W/(m·K) at 100°C (316)
- Specific Heat Capacity: 500 J/(kg·K) at 100°C
- Modulus of Elasticity: 193 GPa (304); 196 GPa (316)
- Yield Strength (0.2% offset): ≥205 MPa (annealed condition)
- Tensile Strength: ≥515 MPa (annealed condition)
- Elongation: ≥40% (annealed condition)
- Operating Temperature Range: −196°C to +870°C (grade-dependent)
2.3 Surface Finish Options
- Pickled & Passivated (P&P): Standard mill finish with a clean, matte grey appearance; suitable for general industrial use.
- Baer Finish (No. 4): Uniformly matte finish with fine linear grain; provides enhanced corrosion resistance and a professional aesthetic.
- Mirror Polish (8K): High-lustre reflective surface (Ra ≤ 0.1 μm); ideal for pharmaceutical, food-grade, and decorative applications.
- Electropolished: Electrochemical surface treatment achieving Ra ≤ 0.25 μm; removes surface contaminants and enhances passive film integrity for maximum hygienic performance.
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 3.175 mm (⅛") – 101.6 mm (4") | ASTM A213 / ASME B36.19M |
| Wall Thickness | 0.4 mm – 6.35 mm (Schedule 5S – Schedule 80S) | ASME B36.19M |
| Coil Diameter (Center-to-Center) | 1.0 m – 4.0 m (adjustable per order) | Manufacturer Specification |
| Coil Length | Up to 500 m per coil (continuous) | Manufacturer Specification |
| OD Tolerance | ±10% (for OD ≤ 12.7 mm); ±0.5 mm (for OD > 12.7 mm) | ASTM A213 |
| Wall Thickness Tolerance | ±10% | ASTM A213 |
| Roundness | ≤10% of nominal wall thickness | ASTM A213 |
| Straightness (per 3 m) | ≤3 mm deviation | ASTM A213 |
| End Condition | Plain cut (standard); Beveled ends available on request | ASME B31.3 |
| Testing | Hydrostatic pressure test, Eddy current inspection, Spectroscopic analysis (PMI) | ASTM A213 / EN 10216-5 |
| Packaging | Wooden pallet with stretch wrap; optional VCI (Vapor Corrosion Inhibitor) paper wrapping | ISO 11607 (for pharma-grade) |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement & Inspection: Hot-rolled stainless steel strip or wire rod is sourced from certified mills (e.g., Outokumpu, POSCO, Taigang). Incoming material undergoes spectroscopic verification (PMI) to confirm chemical composition and visual inspection for surface defects.
- Slitting & Leveling: The strip is slit to the precise width required for the target tube OD and wall thickness, then leveled to ensure uniform flatness prior to forming.
- Continuous Forming (Pipe Mill): The leveled strip is fed into a multi-stand forming mill with progressive roll sets that incrementally bend the strip into a circular cross-section. The forming rolls are precision-ground to ensure dimensional accuracy.
- Seam Welding: The formed tube passes through a High-Frequency Induction Welding (HFIW) station where the seam edges are heated to melting temperature and simultaneously pressure-welded. The welding parameters (frequency, current, roll pressure) are precisely controlled and monitored in real time.
- Online Eddy Current Inspection: The welded tube is immediately subjected to high-frequency eddy current testing to detect seam defects, wall thickness variations, and surface anomalies. Defective sections are automatically marked and removed.
- Coiling: The inspected tube is wound onto a large-diameter coiling mandrel to form the helical coil. Tension and speed are carefully controlled to prevent ovalization, kinking, or work-hardening during coiling.
- Post-Weld Heat Treatment (PWHT): Where required by specification (e.g., for sensitized grades or heavy-wall tubes), the coil undergoes solution annealing at 1050–1150°C followed by rapid air or water quenching to restore full austenitic structure and maximum corrosion resistance.
- Pickling & Passivation: The coil is treated with a controlled acid bath (typically HNO₃/HF blend) to remove mill scale and oxide layers, followed by passivation to re-establish a protective chromium oxide film on the surface.
- Hydrostatic Pressure Testing: Each coil is subjected to a hydrostatic pressure test at 1.5× the maximum design working pressure to verify the integrity of the weld seam and tube body. The test pressure is typically calculated per ASTM A213 or ASME B31.3.
- Final Inspection & Packaging: Dimensional verification (OD, wall thickness, coil diameter), surface quality assessment, and material traceability documentation are completed. The coil is then packaged per customer requirements.
4.2 Advanced Process Features
- Orbital TIG Welding Option: For critical applications (pharmaceutical, aerospace), seamless orbital TIG (Tungsten Inert Gas) welding is available as an alternative to HFIW, producing superior weld quality with minimal heat-affected zone (HAZ).
- In-Line Polish & Electropolishing: Integrated electropolishing lines can achieve Ra ≤ 0.25 μm surface finish directly on the coil without the need for post-coiling individual tube processing.
- Real-Time Process Monitoring: Automated sensors monitor welding parameters, tube diameter, and wall thickness throughout production, with data logged for full traceability.
5. Applications
5.1 HVAC & Fan Coil Units (FCU) in Commercial Buildings
The primary application context for this Coiltube product is the manufacture of fan coil units used in densely populated commercial buildings — including shopping malls, office complexes, hotels, hospitals, and transit stations. In such environments, the coil tube serves as the heat exchange element within the FCU, transferring thermal energy between the refrigerant (or heating medium) and the circulated air.
A critical consideration in densely populated commercial spaces is indoor humidity control. Inadequately designed or manufactured coil tubes can lead to:
- Excessive moisture accumulation on the coil surface due to poor heat transfer efficiency
- Condensate dripping from undersized or improperly pitched drain pans
- Mold and bacterial growth in stagnant condensate areas, degrading Indoor Air Quality (IAQ)
- Increased energy consumption due to latent heat load management failures
Jixing Metal's Coiltube addresses these challenges through:
- Uniform wall thickness and precise OD tolerances — ensuring consistent heat transfer coefficients across the entire coil surface
- Seamless continuous construction — eliminating leak points that could cause moisture ingress into building structures
- Superior surface finish options (electropolished, mirror polished) — reducing biofilm adhesion and facilitating condensate drainage
- Custom coil geometry — optimized tube pitch and coil diameter to maximize surface area-to-volume ratio for efficient dehumidification
5.2 Additional Application Domains
- Food & Beverage Processing: CIP (Clean-in-Place) systems, pasteurization lines, brewing equipment, dairy processing plants
- Pharmaceutical Manufacturing: GMP-compliant piping for water-for-injection (WFI), purified water (PW) systems, steam sterilization loops
- Chemical & Petrochemical: Reactor coils, heat exchanger bundles, process piping for aggressive chemical media
- Power Generation: Solar thermal collectors, geothermal heat exchange loops, nuclear secondary coolant systems
- Automotive & Aerospace: Turbocharger exhaust manifolds, fuel injection lines, hydraulic systems
- Marine & Offshore: Ballast water treatment systems, seawater cooling circuits, desalination plants
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certification portfolio to ensure compliance with international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — certifies systematic quality control across all production processes |
| ISO 14001:2015 | Environmental Management System — certifies environmentally responsible manufacturing practices |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| EN 10204-3.1 | Inspection Certificate — independent third-party material and product verification |
| EN 10216-5 | European standard for seamless and welded stainless steel tubes — product conformity |
| ASTM A213 | American standard for seamless, austenitic stainless steel tubes for high-temperature service |
| ASME B31.3 | Pressure Piping Code — suitability for process piping applications |
| 3-A Sanitary Standards | Food Industry Equipment Association — hygienic design and material requirements |
| CE Marking | European Conformity — compliance with EU directives for product safety |
| NACE MR0175 / ISO 15156 | Resistance to sulfide stress cracking in oil and gas environments (for 316/316L grades) |