Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered, continuous-length tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed for demanding thermal and fluid transport applications, this product is supplied in a coiled configuration to facilitate downstream forming, bending, and installation processes without the introduction of weld seams or mechanical joints.
The Coiltube is particularly engineered to address the requirements of the Pressure Regulation and Constant Speed Method for Matching Fan Coil Units (调压定转速法匹配风机盘管), a system-level control strategy employed in modern HVAC (Heating, Ventilation, and Air Conditioning) installations. In this methodology, the coil tube serves as the primary heat exchange conduit within fan coil units, where precise dimensional tolerances, uniform wall thickness, and superior thermal conductivity are critical to achieving stable pressure differentials and consistent airflow performance across variable operating conditions.
Key advantages of the coiled configuration include:
- Elimination of butt-weld joints, thereby reducing potential leak paths
- Reduced material waste during downstream processing
- Enhanced structural integrity through seamless continuous forming
- Facilitated on-site installation with minimal cutting and fabrication
2. Material & Properties
2.1 Base Alloy Composition
The Coiltube is manufactured from austenitic stainless steel conforming to recognized international standards. The primary alloy grades offered are as follows:
| Grade Designation | UNS Number | C (max) | Cr (%) | Ni (%) | Mn (max) | Si (max) | Application Focus |
|---|---|---|---|---|---|---|---|
| 304 / 304L | S30400 / S30403 | 0.08 / 0.03 | 18.0–20.0 | 8.0–10.5 | 2.0 | 0.75 | General-purpose HVAC, food processing |
| 316 / 316L | S31600 / S31603 | 0.08 / 0.03 | 16.0–18.0 | 10.0–14.0 | 2.0 | 0.75 | Corrosive environments, marine, chemical |
| 321 | S32100 | 0.08 | 17.0–19.0 | 9.0–12.0 | 2.0 | 0.75 | Elevated temperature service |
| 310S | S31008 | 0.08 | 19.0–21.0 | 24.0–26.0 | 2.0 | 0.75 | High-temperature industrial applications |
2.2 Mechanical Properties
| Property | 304 Grade | 316 Grade | 321 Grade | Test Standard |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 | ASTM A270 / GB/T 12771 |
| Yield Strength (0.2% Proof, MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ASTM A270 / GB/T 12771 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ASTM A270 / GB/T 12771 |
| Hardness (HB, Annealed) | ≤ 201 | ≤ 201 | ≤ 201 | ASTM A270 |
2.3 Thermal and Physical Properties
- Thermal Conductivity (at 25°C): 16.3 W/(m·K) for 304 grade; 14.6 W/(m·K) for 316 grade
- Coefficient of Thermal Expansion (20–100°C): 17.3 × 10⁻⁶ /K
- Specific Heat Capacity (at 25°C): 0.50 J/(g·K)
- Density: 8.00 g/cm³ (304); 8.03 g/cm³ (316)
- Operating Temperature Range: −196°C to +870°C (304); −196°C to +870°C (316)
2.4 Corrosion Resistance
The austenitic microstructure provides exceptional resistance to general atmospheric corrosion, intergranular corrosion, and pitting. The 316 grade, with its 2.0–3.0% molybdenum (Mo) addition, offers superior resistance to chloride-induced stress corrosion cracking (Cl-SCC) and pitting, making it the preferred grade for coastal, marine, and chemical processing environments.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification Range | Tolerance | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ108.0 mm | ±0.1 mm (small OD); ±0.2 mm (large OD) | ASTM A270 / GB/T 12771 |
| Wall Thickness (WT) | 0.3 mm – 6.0 mm | ±10% of nominal | ASTM A270 / GB/T 12771 |
| Coil Length (per roll) | 10 m – 500 m (customizable) | — | Manufacturer specification |
| Coil Inner Diameter | 150 mm – 600 mm | ±10 mm | Manufacturer specification |
| Coil Outer Diameter | 400 mm – 1200 mm | ±15 mm | Manufacturer specification |
| Straight Length (optional) | 3 m – 12 m | ±5 mm | Customer requirement |
| Roundness (out-of-roundness) | ≤ 0.5% of OD | — | ASTM A270 |
| Surface Finish | 2B, BA (Bright Annealed), No.4 Hairline, Mirror (8K) | — | ASTM A480 |
| End Condition | Plain, Beveled, Threaded (optional) | — | Customer requirement |
3.2 Common Size Designations (Imperial / Metric)
| NPS (Nominal Pipe Size) | OD (mm) | WT Schedule (mm) | Equivalent Metric (mm) | Typical Application |
|---|---|---|---|---|
| 1/4" | 6.35 | 0.51 – 1.65 | Φ6.35 × 0.5–1.65 | Capillary tubing, instrumentation |
| 1/2" | 13.72 | 0.89 – 3.05 | Φ12.7 × 0.8–3.0 | Small-bore fluid lines |
| 3/4" | 21.34 | 1.10 – 3.68 | Φ21.3 × 1.0–3.7 | HVAC coil piping |
| 1" | 26.67 | 1.10 – 4.57 | Φ26.7 × 1.0–4.6 | Process piping, heat exchangers |
| 1.5" | 41.91 | 1.52 – 5.56 | Φ41.9 × 1.5–5.6 | Medium-pressure systems |
| 2" | 48.26 | 1.65 – 7.11 | Φ48.3 × 1.6–7.1 | Industrial process lines |
| 3" | 73.03 | 2.11 – 8.74 | Φ73.0 × 2.1–8.7 | Large-diameter transfer lines |
| 4" | 101.60 | 2.77 – 10.97 | Φ101.6 × 2.8–11.0 | Heavy-duty industrial applications |
3.3 Product Identification (Product No. 1462)
Product No. 1462 refers to a specific catalog entry within the Wenzhou Jixing Metal Materials Co., Ltd product database. This designation corresponds to a coil tube configuration optimized for HVAC fan coil unit integration, incorporating dimensional and material specifications aligned with the Pressure Regulation and Constant Speed Matching methodology. The product is categorized under the Documentary Learning (文献学习) classification, indicating its association with technical reference materials and engineering study resources for system designers and installation professionals.
4. Manufacturing Process
4.1 Process Flow
- Raw Material Receiving and Inspection: Stainless steel coils are received from certified mills (e.g., Outokumpu, POSCO, Baosteel) and subjected to incoming quality control, including chemical composition verification (OES — Optical Emission Spectroscopy), mechanical property testing, and visual surface inspection.
- Decoiling and Leveling: The raw coil is uncoiled and passed through a precision leveling mill to eliminate mill curvature and ensure flatness within ±0.1 mm/m.
- Slitting: The leveled strip is slit to the required width using a high-precision slitting line with hydraulic blade adjustment, ensuring edge quality and dimensional accuracy.
- Pipe Forming (Cold Roll Forming / ERW): The slit strip is fed through a series of progressive forming rolls that progressively bend the flat strip into a tubular shape. For smaller diameters, cold roll forming is employed; for larger diameters, Electric Resistance Welding (ERW) may be utilized followed by welding seam grinding and polishing.
- Welding Seam Treatment: The formed weld seam is ground flush and polished to achieve a smooth internal surface, minimizing flow turbulence and ensuring hydraulic efficiency. In the case of seamless variants, the weld seam is entirely absent.
- Sizing and Straightening: The formed tube passes through a sizing die to achieve the final OD and wall thickness within specified tolerances, followed by straightening to ensure axial alignment.
- Heat Treatment (Annealing): The tube is annealed in a protective atmosphere (nitrogen or vacuum) to relieve residual stresses from cold working, restore ductility, and achieve the desired microstructure. This step is critical for the subsequent coil winding process.
- Pickling and Passivation: The annealed tube is pickled to remove surface scale and oxide, followed by passivation treatment to form a chromium-rich passive oxide layer that enhances corrosion resistance.
- Surface Finishing: Depending on the specified finish grade (2B, BA, No.4, or Mirror), additional polishing or brushing operations are performed.
- Coil Winding: The finished tube is wound onto a coil former with controlled tension to prevent kinking or deformation. The coil is secured with strapping and protective wrapping.
- Final Quality Inspection: Each coil undergoes dimensional verification (OD, WT, length), surface inspection, hydrostatic or pneumatic pressure testing, and non-destructive testing (NDT) as required.
- Packaging and Dispatch: The inspected coil is wrapped in protective plastic film, secured on a wooden pallet or steel stand, and labeled with the product identification number, material grade, and batch traceability information.
4.2 Key Process Controls
- Dimensional Control: In-line laser measurement systems monitor OD and WT in real time, with automatic corrective feedback to the forming rolls.
- Surface Quality: Automated surface inspection cameras detect scratches, dents, and inclusions, triggering automatic rejection of non-conforming sections.
- Chemical Traceability: Each production batch is linked to mill certificates of analysis (CoA), ensuring full material traceability from raw coil to finished product.
- Pressure Testing: Hydrostatic testing at 1.5× the maximum design pressure (MWP) for a minimum dwell time of 5 seconds per tube length confirms structural integrity.
5. Applications
5.1 HVAC Systems — Fan Coil Unit Integration
The primary application context for Product No. 1462 is within HVAC systems employing fan coil units (FCUs). In the Pressure Regulation and Constant Speed Matching Method, the coil tube functions as the refrigerant or hot water circuit conduit within the FC