Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubular product designed for continuous coiled delivery, enabling seamless integration into automated forming, welding, and heat exchanger assembly lines. This product is particularly renowned for its application in fan coil unit (FCU) systems, where it serves as the core heat transfer element within condensate water collection and drainage subsystems.
Coiltube products offer distinct advantages over straight-length tubing, including reduced material waste, improved metallurgical consistency due to continuous production, and enhanced dimensional uniformity along the tube length. The coil configuration allows for efficient downstream processing, including bending, cutting, and brazing operations without the need for additional welding joints that could compromise structural integrity or thermal performance.
Industry Note: In HVAC (Heating, Ventilation, and Air Conditioning) applications, coil tubes are integral to fan coil units where condensate water management is critical. Improper design or material selection can lead to condensate accumulation, microbial growth, and system inefficiency — challenges that high-quality stainless steel coil tubes are specifically engineered to mitigate.
2. Material Composition & Properties
2.1 Grade Options
- AISI 304 (UNS S30408) — Austenitic stainless steel with excellent general corrosion resistance, widely used in HVAC and food-grade applications.
- AISI 316 (UNS S31608) — Molybdenum-enhanced austenitic grade offering superior resistance to chlorides and acidic environments.
- AISI 321 (UNS S32100) — Stabilized grade with titanium addition for enhanced resistance to intergranular corrosion at elevated temperatures.
- AISI 316L (UNS S31603) — Low-carbon variant of 316, optimized for welding applications and resistance to sensitization.
2.2 Mechanical Properties (Typical for AISI 304)
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa (74,700 psi) | ASTM A270 / ASTM E8 |
| Yield Strength (屈服强度) | ≥ 205 MPa (29,700 psi) | ASTM A270 |
| Elongation (延伸率) | ≥ 40% (0.5 inch gage) | ASTM A270 |
| Hardness (硬度) | ≤ 92 HRB | ASTM A270 |
| Thermal Conductivity (热导率) | 16.3 W/(m·K) at 100°C | ASTM E1461 |
| Operating Temperature Range | −196°C to +870°C | — |
2.3 Chemical Composition (AISI 304, wt%)
| Element | Maximum / Range |
|---|---|
| Carbon (C) | ≤ 0.08% |
| Chromium (Cr) | 18.0 – 20.0% |
| Nickel (Ni) | 8.0 – 10.5% |
| Manganese (Mn) | ≤ 2.0% |
| Silicon (Si) | ≤ 1.0% |
| Phosphorus (P) | ≤ 0.045% |
| Sulfur (S) | ≤ 0.030% |
| Iron (Fe) | Balance |
3. Product Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A270 / ASME B36.19M |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm (0.020" – 0.118") | ASTM A270 |
| Coil Length | 100 m – 500 m per coil (continuous) | — |
| Coil Inner Diameter (ID) | 150 mm – 600 mm | — |
| Surface Finish | 2B, BA (Bright Annealed), No. 4, No. 8, Mirror (Ra ≤ 0.05 μm) | ASTM A480 |
| Seam Type | Welded (automatic argon arc) or Double-Welded | ASME BPV Section I |
| Weld Bead Height | ≤ 0.1 × Wall Thickness | ASTM A270 |
| OD Tolerance | ±0.05 mm (for OD ≤ 25 mm); ±0.10 mm (for OD > 25 mm) | ASTM A270 |
| WT Tolerance | ±10% of nominal | ASTM A270 |
| Roundness | ≤ 5% of nominal OD | ASTM A270 |
| Material Condition | Annealed (Soft), Half-Hard, or Hard | ASTM A270 |
| End Treatment | Plain, Beveled, or Threaded | — |
4. Manufacturing Process
4.1 Process Flow
- Strip Preparation: Cold-rolled stainless steel strip (slit from coil) is inspected for surface quality, width tolerance, and mechanical properties. Strip is uncoiled and fed into the tube mill.
- Tubular Forming: The flat strip passes through a series of progressively shaped roll stands (typically 6–12 stands) that gradually curl and form the strip into a tubular cross-section. Precision roll calibration ensures consistent OD and WT.
- Welding: The formed tube is longitudinally welded using a high-frequency induction (HFI) or automatic argon arc welding (TIG/PAW) process. The welding parameters are controlled to minimize heat-affected zone (HAZ) width and ensure weld integrity.
- Post-Weld Heat Treatment: Welded tubes undergo solution annealing (固溶退火) at 1050–1150°C followed by rapid water quenching to restore full austenitic structure and achieve maximum corrosion resistance.
- Pickling & Passivation: Tubes are subjected to acid pickling (HNO₃/HF mixture) to remove oxide scale, followed by passivation treatment to establish a protective chromium oxide film.
- Surface Finishing: Depending on specification, tubes may undergo polishing (mechanical or electrolytic), electropolishing, or peening to achieve the required surface roughness.
- Dimensional Inspection: In-line laser measurement systems verify OD, WT, and roundness continuously. Samples are tested for hydrostatic pressure (液压试验) per ASTM A270.
- Coiling & Packaging: Finished tubes are wound onto coils with controlled tension to prevent deformation. Coils are wrapped in protective film, strapped, and palletized for shipment.
4.2 Quality Control Measures
- 100% hydrostatic pressure testing at 2.5–3.0 × working pressure for minimum 15 seconds
- Visual inspection of weld seam (dye penetrant testing per ASTM E709 for random samples)
- Chemical composition verification via spark OES (Optical Emission Spectroscopy)
- Mechanical property testing per batch (tensile, hardness, elongation)
- Surface roughness measurement via profilometer (Ra, Rz parameters)
5. Applications
5.1 HVAC — Fan Coil Units (FCU)
The primary application domain for this coil tube product is the manufacturing of fan coil units, where the coil tube forms the heat exchange core. The condensate water tray problem — a common failure mode in FCU systems — is effectively addressed by using high-quality stainless steel coil tubes with:
- Optimized tube pitch and fin spacing to promote uniform condensate drainage
- Smooth inner surface finish to minimize scale buildup and maintain flow efficiency
- Corrosion-resistant material selection to prevent pitting that could obstruct drainage paths
5.2 Additional Application Areas
- Food & Beverage Industry: Heat exchangers, sanitary piping, and processing equipment (316L grade)
- Pharmaceutical Equipment: Clean-in-place (CIP) systems, autoclave tubing, and reactor components
- Automotive: Exhaust system components, fuel lines, and condenser tubes
- Chemical Processing: Heat exchanger tubes, condensers, and reactor internals (316/321 grades)
- Marine & Offshore: Seawater cooling systems, ballast piping, and desalination plant components
- Power Generation: Boiler tubes, feedwater heaters, and condenser tube bundles
- Domestic Appliances: Water heater elements, dishwasher components, and HVAC condensate lines
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| CE Marking (EU) | European Conformity for pressure equipment |
| ASME BPV Code Section I | Boiler and Pressure Vessel Code compliance |
| EN 10216-5 | European standard for austenitic stainless steel tubes |
| ASTM A270 / A554 | American standards for stainless steel tubing |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes |
| NSF/ANSI 61 | Drinking water system components (where applicable) |
| PED 2014/68/EU | Pressure Equipment Directive compliance |
7. Unique Selling Points
- Superior Corrosion Resistance: High chromium (18–20%) and nickel (8–10.5%) content ensures long service life in aggressive environments, particularly addressing the condensate water corrosion challenge in FCU systems.
- Continuous Coil Delivery: Eliminates butt-weld joints inherent in straight pipe, reducing leak risk and improving thermal uniformity in heat exchanger applications.
- Multi-Grade Availability: Comprehensive grade range (304, 316, 316L, 321) allows precise material selection for specific service conditions.
- Precision Manufacturing: Tight dimensional tolerances (±0.05 mm OD) and controlled weld bead geometry ensure consistent downstream processing and assembly.
- Comprehensive Surface Options: From industrial 2B finish to mirror polish (Ra ≤ 0.05 μm), accommodating both functional and aesthetic requirements.
- Full Traceability: Each coil is accompanied by a mill test certificate (MTC) with heat number, chemical analysis, mechanical test results, and dimensional verification data.
- Customization Capability: Non-standard OD, WT, surface finish, and coil dimensions available upon request through engineering consultation.
8. Technical Advisory Note
Based on extensive field experience and technical literature review regarding fan coil unit condensate water tray problems, the following design considerations are recommended when specifying stainless steel coil tubes for FCU applications:
- Maintain minimum tube pitch of 25.4 mm (1") to ensure adequate condensate drainage flow area
- Select BA or polished surface finish to minimize biofilm adhesion on tube surfaces
- Specify 316L grade for installations in coastal or high-humidity environments where chloride-induced pitting is a concern
- Ensure tube ends are deburred and chamfered to prevent condensate stagnation at connection points
- Design coil slope (≥ 0.5%) to promote gravity-assisted condensate removal
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Reference No.: 1291
Classification: Literature Study — Technical Solutions for HVAC Coil Systems