Stainless Steel Coil Tube (Coiltube) — Product No. 774
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), designated as Product No. 774, is a precision-engineered continuous-length stainless steel tubing supplied in a coiled configuration. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product is designed for demanding thermal-fluid transfer applications, including central air conditioning fan coil units, HVAC (Heating, Ventilation, and Air Conditioning) systems, refrigeration circuits, and industrial heat exchangers.
The coil tube format offers significant advantages over straight-length tubing: reduced cutting waste, enhanced flexibility during installation, superior coilability for compact heat exchanger geometries, and improved material utilization efficiency. The product is particularly suited for integration with automated temperature control systems, such as those based on microcontroller platforms (e.g., STC51W408AS MCU-based fan coil temperature controllers), where precise thermal management and reliable fluid containment are critical.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards, with the following typical grades available:
- ASTM A213 TP304 / TP304L — General-purpose corrosion-resistant tubing with excellent formability
- ASTM A213 TP316 / TP316L — Molybdenum-enhanced grade for superior resistance to chlorides and pitting corrosion
- ASTM A213 TP321 / TP347 — Stabilized grades for elevated-temperature service with reduced sensitization risk
2.2 Mechanical Properties (Annealed Condition)
| Property | ASTM A213 TP304 | ASTM A213 TP316 | ASTM A213 TP321 |
|---|---|---|---|
| Tensile Strength (UTS), min (MPa) | 515 | 515 | 515 |
| Yield Strength, 0.2% offset (MPa), min | 205 | 205 | 205 |
| Elongation in 50 mm, min (%) | 35 | 35 | 35 |
| Thermal Conductivity (W/m·K) @ 100°C | 16.3 | 14.6 | 16.3 |
| Thermal Expansion Coefficient (×10⁻⁶/K) @ 20–100°C | 17.3 | 16.0 | 17.3 |
| Maximum Service Temperature (°C) | 870 | 870 | 1095 |
2.3 Chemical Composition (Typical, wt%)
| Grade | C (max) | Mn (max) | P (max) | S (max) | Si (max) | Cr | Ni | Mo | Ti |
|---|---|---|---|---|---|---|---|---|---|
| 304 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 18.0–20.0 | 8.0–10.5 | — | — |
| 316 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | — |
| 321 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0–19.0 | 9.0–12.0 | — | 5×(C+0.02)–0.70 |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (Coiltube) — Product No. 774 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
| Supply Form | Continuous coil (Coiltube), wound on standard steel or wooden spools |
| Outside Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2"), per ASTM A213 |
| Wall Thickness | 0.5 mm – 3.0 mm (B.W.G. 16 – 12), tolerance ±10% |
| Coil Length | 100 m – 500 m per coil (custom lengths available upon request) |
| Coil Weight | 500 kg – 3,000 kg per spool (depending on OD and wall thickness) |
| Surface Finish | Mirror polished (Ra ≤ 0.05 μm), Electropolished (EP), or 2B/No. 4 brushed |
| Heat Treatment | Solution annealed and water quenched (SA condition) |
| Applicable Standards | ASTM A213 / A269, ASME SA-213 / SA-269, EN 10216-5, GB/T 14976 |
| Coil Winding Diameter | Minimum coil diameter (MCD): 3× OD (for OD ≤ 25 mm); 4× OD (for OD > 25 mm) |
| Packaging | Inner PE film wrapping + outer kraft paper + VCI (Volatile Corrosion Inhibitor) + wooden/steel spool |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage process ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Ingot Casting: High-purity stainless steel slabs are produced via the AOD (Argon Oxygen Decarburization) or VOD (Vacuum Oxygen Decarburization) secondary refining process, ensuring tight control of carbon, sulfur, and nitrogen residuals.
- Hot Rolling & Pickling: Slabs are hot-rolled into coils and subjected to acid pickling (HNO₃/HF mixed acid) to remove the mill scale, revealing the clean metallic surface.
- Cold Drawing / Cold Reduction: The hot-rolled coil is cold-drawn through a series of calibrated tungsten carbide dies to achieve the required outer diameter (OD) and wall thickness with tolerance of ±10%.
- Solution Annealing: Drawn tubing is solution-annealed at 1050–1150°C in a protective atmosphere (endothermic gas or vacuum) followed by rapid water quenching. This process recrystallizes the cold-worked microstructure, restores full ductility, and achieves the desired austenitic grain structure.
- Precision Coiling: The annealed tubing is coiled onto spools using automated coil winding equipment, maintaining uniform tension to prevent ovality, kinks, or mechanical deformation.
- Surface Finishing: Depending on application requirements, tubing undergoes mirror polishing (multi-step electrolytic polishing or mechanical buffing), electropolishing (EP), or mechanical brushing to achieve specified surface roughness.
- Quality Inspection: Each batch undergoes hydrostatic pressure testing (per ASTM A213), eddy current testing (ECT) for wall thickness and defect detection, and dimensional verification using laser gauging systems.
- Packaging & Dispatch: Finished coils are wrapped, protected, and prepared for export or domestic distribution.
5. Applications
5.1 HVAC & Fan Coil Systems
Stainless steel coil tubes are the primary heat exchange medium in fan coil units (FCUs) for central air conditioning systems. In modern intelligent HVAC architectures — such as those controlled by microcontroller-based temperature controllers (e.g., STC51W408AS MCU platforms) — the coil tube must deliver consistent thermal performance, long-cycle fatigue resistance, and resistance to condensation corrosion. The austenitic stainless steel composition ensures compatibility with both water-based and refrigerant-based fluid circuits.
5.2 Additional Application Domains
- Refrigeration & Cryogenics: Evaporator and condenser tubing for ammonia, R-134a, R-410A, and CO₂ refrigerant systems
- Food & Beverage Processing: Sanitary-grade tubing for dairy, brewing, and pharmaceutical fluid transfer (316L grade, Ra ≤ 0.25 μm)
- Chemical Processing: Process tubing for acid-alkali resistant heat exchangers and reactor cooling systems
- Automotive Industry: A/C condenser and evaporator tubing for passenger vehicles and commercial fleets
- Power Generation: Boiler tubing, superheater tubes, and heat recovery steam generators (HRSG)
- Marine & Offshore: Seawater heat exchanger tubing resistant to chloride-induced stress corrosion cracking (SCC)
6. Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing operations |
| ISO 14001:2015 | Environmental Management System certification |
| ASTM A213 / A269 | Material and dimensional compliance for seamless stainless steel tubing |
| ASME SA-213 / SA-269 | Pressure vessel and heat exchanger tubing qualification |
| EN 10216-5 | European standard for stainless steel seamless tubes for heat exchangers |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for heat exchangers |
| Mill Test Reports (MTR) | Chemical composition, mechanical properties, and heat treatment records provided per lot |
| CE Marking | Conformity with European pressure equipment directive (PED 2014/68/EU) |
7. Unique Selling Points
- Superior Coilability: Solution-annealed austenitic microstructure provides exceptional formability, enabling minimum bend radii of 3× OD without cracking — critical for compact fan coil and heat exchanger designs.
- Intelligent System Compatibility: Designed for seamless integration with microcontroller-based HVAC control architectures (e.g., STC51W408AS-based temperature controllers), ensuring reliable thermal cycling performance under automated control loops.
- Multi-Grade Availability: Comprehensive product range spanning 304, 316, 321, and 347 grades accommodates diverse corrosion and temperature requirements without design redesign.
- Traceability & Documentation: Full lot-level traceability with certified Mill Test Reports (MTR) and positive material identification (PMI) documentation ensures regulatory compliance for critical applications.
- Cost-Effective Continuous Supply: Coil format eliminates butt-weld joints, reducing installation labor and improving system integrity while minimizing material waste during fabrication.