Stainless Steel Coil Tube (Evaporative Cooling Coiltube)
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered coiled tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed primarily for evaporative cooling systems, heat exchangers, and thermal management applications, this product combines superior corrosion resistance with excellent thermal conductivity. The coil geometry enables compact installation within tight spatial constraints while maximizing surface area for efficient heat and mass transfer.
Extensive research has been conducted on the performance characteristics of these coil tubes under varying wind-water arrangements and pipe diameters. Studies have demonstrated that optimizing the spatial configuration of the coiltube relative to airflow direction and water distribution patterns significantly enhances evaporative cooling efficiency and surface wetting uniformity. This product line reflects the culmination of such engineering insights, delivering consistent performance across diverse operating conditions.
2. Material & Properties
2.1 Base Material
- Grade Options: AISI 304 (UNS S30400), AISI 316L (UNS S31603), AISI 321 (UNS S32100), and custom alloy compositions
- Composition (304 Grade): Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Carbon (C) ≤0.08%, Manganese (Mn) ≤2.0%
- Composition (316L Grade): Chromium (Cr) 16.5–18.5%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%, Carbon (C) ≤0.03%
2.2 Physical & Mechanical Properties
| Property | AISI 304 | AISI 316L |
|---|---|---|
| Density (g/cm³) | 8.00 | 8.00 |
| Thermal Conductivity at 25°C (W/m·K) | 16.3 | 14.6 |
| Thermal Conductivity at 500°C (W/m·K) | 21.5 | 19.8 |
| Tensile Strength (MPa, min) | 515 | 485 |
| Yield Strength (MPa, min) | 205 | 170 |
| Elongation (% , min) | 40 | 40 |
| Maximum Service Temperature (°C) | 870 | 870 |
| Corrosion Resistance (Pitting) | Good | Excellent |
2.3 Surface Characteristics
- Surface Finish: 2B, BA (Bright Annealed), No. 4 brushed, or custom polishing to Ra ≤ 0.4 μm
- Wetting Performance: Contact angle ≤ 65° on BA finish, ensuring uniform water film formation during evaporative cooling cycles
- Anti-Fouling Coating (Optional): Hydrophilic nano-coating available for enhanced water distribution uniformity
3. Specifications
| Parameter | Specification Range | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 – Φ50.8 mm (1/4" – 2") | ASTM A554 / EN 10217 |
| Wall Thickness | 0.30 – 3.00 mm | ASTM A554 |
| Coil Diameter (Pitch Diameter) | Φ50 – Φ500 mm | Custom per application |
| Coil Length (Uncoiled) | Up to 1,000 m continuous | — |
| Coil Pitch (Turn-to-Turn) | 1.2 × OD to 3.0 × OD | ASME B31.3 |
| Number of Turns | 2 – 500 turns | — |
| Tolerance on OD | ±0.05 mm (precision); ±0.15 mm (standard) | ASTM A554 |
| Tolerance on Wall Thickness | ±10% (standard); ±5% (precision) | EN 10217-7 |
| Maximum Operating Pressure | Up to 4.0 MPa (depending on geometry) | ASME B31.3 |
| Operating Temperature Range | -196°C to +870°C | ASME BPVC Section VIII |
| Heat Transfer Coefficient (Convective) | 1,500 – 4,500 W/m²·K (evaporative cooling) | Empirical correlation (Dittus-Boelter) |
| End Forming | Plain, flanged, threaded, or crimped | Per customer drawing |
3.1 Recommended Pipe Diameter Selection for Evaporative Cooling
| Application | Recommended OD (mm) | Recommended Wall Thickness (mm) | Rationale |
|---|---|---|---|
| Air Conditioning Coils | 9.5 – 12.7 | 0.50 – 0.80 | Optimal balance of heat transfer area and pressure drop |
| Industrial Evaporative Coolers | 15.9 – 25.4 | 0.80 – 1.20 | Higher flow capacity with uniform water distribution |
| Cryogenic Applications | 6.0 – 12.7 | 0.30 – 0.60 | Thin-wall for rapid thermal equilibration |
| Food & Beverage Heat Exchangers | 12.7 – 19.0 | 1.00 – 1.60 | 316L grade for hygienic compliance |
4. Manufacturing Process
4.1 Process Flow
- Hot Rolling: Stainless steel slabs are hot-rolled into seamless tube blanks meeting ASTM A554 dimensional tolerances.
- Piercing & Enlarging: The billets are pierced and sequentially enlarged through multiple passes to achieve target OD and wall thickness.
- Intermediate Annealing: Solution annealing at 1050–1150°C followed by controlled cooling to restore ductility and refine grain structure.
- Cold Drawing / Cold Reduction: Multi-pass cold drawing through tungsten carbide dies to achieve final dimensions with tight tolerances and improved surface finish.
- Precision Coiling (Bending): Computerized CNC coiling machines form the straight tube into helical coils with controlled pitch, diameter, and number of turns. Bend radius is maintained at ≥3× OD to prevent ovality and stress concentration.
- Post-Coil Annealing: Optional stress-relief annealing at 450–550°C to eliminate residual bending stresses without sensitization.
- Pickling & Passivation: Acid pickling (HNO₃/HF blend) followed by passivation treatment to remove scale, restore chromium oxide layer, and ensure corrosion resistance.
- Surface Finishing: Electropolishing, brushing, or coating application as specified.
- Quality Inspection: Dimensional verification, hydrostatic testing, visual inspection, and material certification.
- Packaging: Protective wrapping, moisture barriers, and export-grade palletization.
4.2 Key Process Parameters
- Coiling Temperature: Ambient (cold forming) or pre-heated to 200–350°C (warm forming for larger diameters)
- Bend Rate: Controlled at ≤5 turns/minute to ensure uniform deformation
- Reduction Ratio per Pass: ≤30% for cold drawing; ≤45% for hot rolling
- Grain Structure: ASTM E139 grain size ≥ No. 6 (average grain diameter ≤ 65 μm)
5. Applications
5.1 Primary Applications
- Evaporative Cooling Systems: Coil tubes serve as the primary heat exchange element in direct evaporative coolers, where water is distributed over the coil surface and evaporates to cool incoming air. Research demonstrates that pipe diameter and coil geometry significantly influence water distribution uniformity, with optimal configurations achieving >90% effective wetted surface ratio.
- Air Conditioning & HVAC: Condenser and evaporator coils in commercial and industrial air handling units.
- Industrial Heat Exchangers: Shell-and-coil heat exchangers, condensers, and reboilers in chemical, petrochemical, and pharmaceutical processing.
- Cryogenic Systems: Liquid nitrogen and natural gas heat exchangers requiring reliable performance at extremely low temperatures.
- Food & Beverage Processing: Hygienic heat exchangers for pasteurization, sterilization, and temperature control in dairy, brewing, and beverage industries.
- Power Generation: Steam generators, economizers, and condenser tubes in thermal power plants.
- Marine & Offshore: Seawater-cooled condensers and heat recovery systems where chloride resistance is critical.
5.2 Performance in Evaporative Cooling — Research Insights
Studies on water distribution uniformity across coil tube surfaces under different wind-water configurations have established critical design parameters:
- Pipe diameters of 9.5–12.7 mm with coil pitch of 2.0–2.5× OD achieve the best compromise between wetting efficiency and airflow resistance.
- Wind velocity of 2–4 m/s combined with spray density of 0.5–1.5 L/m²·min maximizes evaporative heat transfer coefficient.
- Coil orientation perpendicular to airflow direction with 30°–45° tilt from horizontal optimizes water film retention and gravitational drainage.
- Surface roughness (Ra 0.2–0.8 μm) on BA-finished coils promotes uniform water film formation compared to rougher surfaces.
6. Quality Certifications & Compliance
6.1 Applicable Standards
| Standard | Scope |
|---|---|
| ASTM A554 / A554M | Austenitic stainless steel cold-worked coil tubing |
| ASTM A269 / A269M | Welded austenitic stainless steel tubing |
| EN 10217-7 | Stainless steel seamless tubes for pressure purposes |
| ASME BPVC Section VIII | Pressure vessel and piping design codes |
| ASME B31.3 | Process piping design and installation |
| ISO 15765 | Corrosion-resistant stainless steel seamless tubes |
| GB/T 12771 | Chinese national standard for stainless steel tubes for general use |
6.2 Certifications & Testing
- Material Certification: EN 10204 3.1 material certificates with full chemical analysis and mechanical test reports
- Hydrostatic Testing: 100% pressure testing at 1.5× maximum working pressure, hold time ≥ 10 seconds
- Non-Destructive Testing (NDT): Eddy current testing (ET) and ultrasonic testing (UT) for weld seam and body integrity
- Dimensional Inspection: 100% OD and wall thickness verification using calibrated calipers and ultrasonic thickness gauges
- Corrosion Testing: Salt spray testing (ASTM B117) ≥ 500 hours without pitting for 316L grade; potentiodynamic polarization testing for corrosion potential verification
- Intergranular Corrosion: ASTM A262 Practice No. 1E for sensitization assessment (316L grade)
- Food Grade Compliance: FDA 21 CFR 178.3010, EC 1935/2004, and 3-A Sanitary Standards (optional)
- Pressure Vessel Stamp: ASME "U" stamp or PED 2014/68/EU Module HD certification available upon request
6.3 Quality Assurance System
- ISO 9001:2015 Quality Management System certified
- ISO 14001:2015 Environmental Management System certified
- ISO 45001:2018 Occupational Health and Safety Management System certified
- In-house Laboratory: Equipped with spectrometer (OES), tensile testing machine, hardness tester, hydrostatic test bench, and optical comparator for full material and dimensional verification
7. Unique Selling Points
- Research-Driven Design: Product specifications are informed by empirical studies on evaporative cooling performance, ensuring optimal coil geometry for maximum heat transfer efficiency.
- Custom Coiling Capability: CNC-controlled coiling allows precise customization of coil diameter, pitch, turn count, and end forming to match specific system layouts.