Stainless Steel Coil Tube (Coiltube) for HVAC Fan Coil Pipeline Systems
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for integration into fan coil unit (FCU) pipeline systems and wind tunnel test apparatus. This product is supplied in a coiled configuration, enabling seamless installation with minimal cutting, welding, and joint fabrication. The coiltube serves as the primary conduit for refrigerant, hydronic fluid, and compressed air within HVAC (Heating, Ventilation, and Air Conditioning) systems, as well as in aerodynamic wind tunnel testing environments where flow uniformity and structural integrity are critical.
The coiltube is engineered to meet the stringent requirements of pipeline system optimization design, as demonstrated in wind tunnel-style fan coil detection apparatus applications. Its geometry, material composition, and surface finish are optimized to minimize flow resistance, reduce pressure drop, and ensure long-term resistance to corrosion, thermal cycling, and mechanical fatigue.
2. Material & Properties
2.1 Material Grades
- AISI 304 (UNS S30400) — Austenitic stainless steel with 18% Chromium and 8% Nickel; offers excellent corrosion resistance and formability. Suitable for general HVAC and hydronic applications.
- AISI 316L (UNS S31603) — Low-carbon austenitic stainless steel with added Molybdenum (2–3%); provides superior resistance to pitting and crevice corrosion. Recommended for aggressive chemical environments and marine HVAC systems.
- AISI 321 (UNS S32100) — Stabilized austenitic grade with Titanium addition; resistant to intergranular corrosion. Suitable for high-temperature pipeline applications exceeding 450°C.
2.2 Mechanical Properties
| Property | AISI 304 | AISI 316L | AISI 321 |
|---|---|---|---|
| Tensile Strength (UTS, MPa) | ≥ 520 | ≥ 520 | ≥ 520 |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation at Break (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HB) | ≤ 217 | ≤ 217 | ≤ 217 |
| Thermal Conductivity (W/m·K, 25°C) | 16.3 | 14.6 | 16.3 |
| Linear Expansion Coefficient (10⁻⁶/K, 20–100°C) | 17.3 | 17.1 | 17.3 |
2.3 Surface Condition
The inner and outer surfaces of the coiltube are available in BA (Bright Annealed) finish for high-purity applications, or 2B (Cold Rolled and Annealed) finish for general industrial use. Surface roughness is maintained at Ra ≤ 0.8 μm for BA finish and Ra ≤ 1.6 μm for 2B finish, ensuring low hydraulic resistance in fluid transport applications.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (Coiltube), Product No. 683 |
| Outer Diameter (OD) | 6 mm – 51 mm (customizable upon request) |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm |
| Coil Inner Diameter (ID) | 200 mm – 800 mm |
| Coil Length per Spool | 30 m – 200 m (adjustable) |
| OD Tolerance | ± 0.05 mm (precision grade); ± 0.1 mm (standard grade) |
| Wall Thickness Tolerance | ± 10% of nominal |
| Coil Straightness | ≤ 2 mm/m |
| Operating Temperature Range | −196°C to +870°C (AISI 304/316L); −196°C to +900°C (AISI 321) |
| Maximum Operating Pressure | Up to 4.0 MPa (dependent on OD and WT) |
| Applicable Standards | ASTM A213/A213M, ASTM A269/A269M, EN 10216-5, GB/T 12771, GB/T 13296 |
| End Form | Plain cut; beveled; grooved; threaded (upon request) |
4. Manufacturing Process
4.1 Seamless Tube Production
- Ingot Casting and Hot Rolling — Raw steel ingots are cast and hot-rolled into seamless tube billets conforming to ASTM A213 specifications.
- Piercing and Elongation — Billets are heated to 1100–1200°C and pierced via rotary piercing mill (RPM) or Mannesmann process to produce seamless hollow tubes.
- Cold Drawing / Cold Rolling — Tubes undergo cold working to achieve precise dimensional tolerances and improved mechanical properties. Multiple passes through draw benches ensure uniform wall thickness.
- Solution Annealing — Cold-worked tubes are solution annealed at 1050–1150°C followed by rapid quenching (water or air) to restore full austenitic microstructure and maximize corrosion resistance.
4.2 Coil Forming and Post-Processing
- Coiling — Annealed tubes are coiled around mandrels of the specified coil inner diameter using a controlled winding system to prevent ovality and deformation.
- Surface Finishing — Electropolishing or chemical pickling is applied to remove surface oxide layers and achieve the specified surface roughness.
- Hydrostatic Testing — Each coil is subjected to hydrostatic pressure testing at 1.5× the maximum operating pressure to verify weld integrity and wall uniformity.
- Dimensional Inspection — Outer diameter, wall thickness, and coil straightness are measured using laser-based dimensional inspection systems.
- Packaging — Coils are wrapped in protective film, wrapped with kraft paper, and secured on wooden pallets or steel coil stands for transport.
5. Applications
- HVAC Fan Coil Unit (FCU) Systems — Primary application for chilled water, hot water, and refrigerant circulation in commercial and industrial air conditioning systems. The coiltube's continuous length eliminates field joints, reducing leak risk.
- Wind Tunnel Test Apparatus — Used in wind tunnel-style fan coil detection devices where optimized pipeline geometry is essential for accurate aerodynamic and thermal performance measurement. The coiltube's smooth inner surface ensures laminar flow characteristics.
- Chilled Beam Systems — Integrated into chilled beam and dry beam HVAC configurations for precise temperature and humidity control in high-end commercial buildings.
- Process Cooling and Heating — Employed in pharmaceutical, food and beverage, and semiconductor manufacturing facilities requiring hygienic, corrosion-resistant fluid transport.
- Marine HVAC Systems — AISI 316L grade coiltubes are specified for marine air conditioning and refrigeration systems exposed to salt-laden environments.
- Geothermal Heat Exchange Systems — Utilized in closed-loop geothermal HVAC systems where long-term durability in underground piping is required.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality certifications and complies with international standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification for environmentally responsible manufacturing practices.
- EN 10204 3.1 — Material Test Report certification providing traceability of chemical composition and mechanical properties.
- CE Marking — Conformity with European health, safety, and environmental protection standards.
- PED 2014/68/EU — Pressure Equipment Directive compliance for pressure-containing pipeline applications.
- GB/T 19001-2016 — Chinese national equivalent of ISO 9001.
6.1 Incoming Material Inspection
All raw steel coils and billets are inspected upon receipt for chemical composition (via optical emission spectrometry, OES), mechanical properties, and surface quality. Non-conforming material is rejected prior to entering the production line.
6.2 In-Process Quality Control
- Online ultrasonic flaw detection (UT) during cold drawing to detect internal voids and inclusions.
- Hardness testing (Rockwell B scale) at regular intervals along the production line.
- Visual inspection of surface finish post-annealing and post-polishing.
6.3 Final Product Inspection
- Dimensional verification using laser calipers and ultrasonic wall thickness gauges.
- Hydrostatic pressure testing at 1.5× working pressure with a minimum hold time of 10 seconds.
- Corrosion resistance testing via salt spray test (ASTM B117) — minimum 500 hours without pitting for AISI 316L grade.
- Coil straightness and ovality measurement using automated optical scanning systems.
7. Unique Selling Points
Seamless Coiled Configuration: The coiltube is supplied in a continuous, pre-coiled format, eliminating the need for field welding and joint fabrication. This reduces installation time by up to 40% and minimizes potential leak points in critical HVAC pipeline systems.
- Wind Tunnel-Optimized Geometry: The coiltube is engineered with precise dimensional tolerances and superior surface finish, making it ideal for wind tunnel testing apparatus where flow uniformity and turbulence minimization are paramount.
- Full Traceability: Each coil is serialized and accompanied by an EN 10204 3.1 material test certificate, ensuring complete traceability from raw material to finished product.
- Customizable Specifications: Wenzhou Jixing offers flexible customization of outer diameter, wall thickness, coil length, and surface finish to meet specific project requirements.
- Extended Service Life: The austenitic stainless steel microstructure provides exceptional resistance to corrosion, thermal fatigue, and mechanical degradation, ensuring a service life exceeding 25 years in demanding HVAC environments.
- Low Hydraulic Resistance: The smooth inner surface (Ra ≤ 0.8 μm) significantly reduces Darcy-Weisbach friction factor, resulting in lower pumping energy consumption and improved system efficiency.
- Hygienic Grade Available: BA (Bright Annealed) finish options meet FDA and 3-A sanitary standards for pharmaceutical and food-grade HVAC applications.
8. Technical Data Reference
| Grade | Cr (%) | Ni (%) | Mn (%) | C (%) | Mo (%) | Ti (%) | Corrosion Resistance Rating |
|---|---|---|---|---|---|---|---|
| AISI 304 | 18.0–20.0 | 8.0–10.5 | ≤ 2.0 | ≤ 0.08 | — | — | Good |
| AISI 316L | 16.5–18.5 | 10.0–14.0 | ≤ 2.0 | ≤ 0.03 | 2.0–3.0 | — | Excellent |
| AISI 321 | 17.0–19.0 | 9.0–12.0 | ≤ 2.0 | ≤ 0.08 | — | 5×C to 0.70 | Good (high-temperature stabilized) |