Stainless Steel Evaporative Cooling Coil Tube (Coiltube) — Closed-Loop Cooling Tower Application
Product Overview
The Stainless Steel Coiltube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous coil tube specifically designed for evaporative cooling systems within closed-loop cooling towers. This product represents a critical component in industrial heat dissipation infrastructure, where efficient heat transfer and mass transfer performance are paramount to system reliability and energy efficiency.
Unlike conventional straight pipe configurations, the coiltube geometry provides a significantly increased surface area-to-volume ratio, enabling superior convective and evaporative cooling performance within compact installations. The continuous coil form factor eliminates the need for field-welded joints, thereby reducing potential leak points and enhancing long-term operational integrity in corrosive cooling environments.
The product line has been extensively validated through rigorous academic and industrial research into evaporative cooling coil tube heat transfer and mass transfer characteristics, ensuring that each coil delivers predictable and optimized thermal performance across a wide range of operating conditions.
Material & Properties
Base Material
- Primary Alloy: Austenitic Stainless Steel — AISI 304 (UNS S30400) and AISI 316L (UNS S31603), with optional 321 (UNS S32100) and 316Ti (UNS S31609) grades available for high-temperature or highly corrosive service.
- Composition (AISI 304): Cr 18–20%, Ni 8–10.5%, C ≤ 0.08%, Mn ≤ 2.0%, Si ≤ 1.0%, P ≤ 0.045%, S ≤ 0.030%.
- Composition (AISI 316L): Cr 16–18%, Ni 10–14%, Mo 2–3%, C ≤ 0.03%, with enhanced pitting and crevice corrosion resistance.
Mechanical Properties
- Tensile Strength: ≥ 515 MPa (304), ≥ 485 MPa (316L)
- Yield Strength (0.2% offset): ≥ 205 MPa (304), ≥ 170 MPa (316L)
- Elongation: ≥ 40% (304), ≥ 45% (316L)
- Hardness: ≤ 217 HB (304), ≤ 210 HB (316L)
Thermal & Corrosion Properties
- Thermal Conductivity: 16.3 W/(m·K) at 25°C (304), 14.6 W/(m·K) at 25°C (316L)
- Operating Temperature Range: −196°C to +870°C (oxidizing atmosphere)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, dilute mineral acids, organic acids, and aqueous salt solutions. 316L grade provides superior resistance to chloride-induced pitting and stress corrosion cracking (SCC).
- Surface Finish: 2B (cold-rolled, annealed, pickled) or No. 4 brushed finish; electropolished surfaces available upon request to minimize biofilm adhesion in cooling water applications.
Specifications
| Parameter | Specification Range | Unit | Notes |
|---|---|---|---|
| Outer Diameter (OD) | 8.0 – 50.8 | mm | Standard sizes: 12.7, 15.9, 19.1, 21.3, 25.4, 31.8, 38.1, 44.4 |
| Wall Thickness (WT) | 0.5 – 3.0 | mm | Custom thickness available; minimum 0.5 mm for thin-wall evaporative service |
| Coil Pitch (Center-to-Center Spacing) | 15 – 60 | mm | Optimized for maximum heat/mass transfer efficiency |
| Coil Diameter | 100 – 800 | mm | Customizable based on tower shell dimensions |
| Coil Length (Total Developed Length) | 1 – 50 | m | Continuous coil; no field welding required |
| Number of Turns | 5 – 200 | — | Dependent on coil diameter and total length |
| End Connection Type | Threaded (BSP/NPT), Flanged (ASME/EN), Soldered, or Welded (TIG) | — | Custom fittings available |
| Tolerance on OD | ±0.10 | mm | Per ASTM A269 / ASTM A270 |
| Tolerance on Wall Thickness | ±10% | — | Per ASTM A269 / ASTM A270 |
| Surface Roughness (Ra) | 0.4 – 1.6 | μm | Lower Ra improves convective heat transfer coefficient |
| Maximum Design Pressure | Up to 1.6 | MPa | Hydrostatic test at 1.5× working pressure |
| Standards Complied | ASTM A269, ASTM A270, ASME B36.19M, EN 10216-5, GB/T 12771 | — | Mutually exclusive or combinable per project requirement |
Manufacturing Process
The production of the stainless steel coiltube at Wenzhou Jixing Metal Materials Co., Ltd. follows a multi-stage precision manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and optimal surface quality:
- Raw Material Procurement & Mill Annealing: Cold-rolled stainless steel strip or seamless tube stock is sourced from certified mills. Incoming material undergoes full chemical composition analysis (via OES or wet chemistry) and mechanical property verification before release to production.
- Coil Forming / Bending: The tube blank is passed through a series of precision roller-forming stations or a CNC-controlled tube bending machine. The bending radius is carefully controlled to exceed the minimum recommended bend radius (typically ≥ 3× OD) to prevent wall thinning, ovalization, or wrinkling. Multi-axis bending allows for helical coil geometries with uniform pitch.
- Post-Form Annealing (Solution Treatment): Following coil formation, the tube is subjected to solution annealing at 1050–1100°C in a controlled atmosphere (nitrogen or argon) furnace, followed by rapid water quenching. This step relieves bending-induced residual stresses, restores full solution-annealed microstructure, and maximizes corrosion resistance.
- Pickling & Passivation: The annealed coil is immersed in a citric acid or nitric-hydrofluoric acid pickling solution to remove any oxide scale formed during heat treatment. Subsequent passivation treatment forms a stable chromium oxide (Cr₂O₃) passive film on the surface, enhancing long-term corrosion protection.
- Dimensional Inspection: Each coil undergoes comprehensive dimensional verification including OD, wall thickness (at multiple points along the developed length), coil pitch uniformity, and end alignment. Optical and ultrasonic testing methods are employed for non-destructive evaluation (NDE).
- Hydrostatic Pressure Testing: Every coil tube is pressure-tested at 1.5× the maximum design working pressure to verify structural integrity and absence of leaks or defects.
- End Finishing & Fitting Installation: Threaded ends, flanges, or other connection hardware are machined or installed per customer specification. Surface finishing (polishing, brushing, or electropolishing) is performed as required.
- Final Packaging: Coils are wrapped in moisture-barrier protective film, labeled with heat lot traceability tags, and packed for shipment with appropriate cushioning to prevent transport damage.
Applications
Primary Application: Closed-Loop Cooling Towers
The principal application domain for this coiltube product is evaporative cooling systems within closed-loop (indirect) cooling towers. In such systems, process fluid flows through the coiltube while ambient air and a water spray pass over the external coil surface. Heat is transferred from the process fluid to the water film, and simultaneous mass transfer (evaporation of water) provides additional cooling capacity. The coiltube's continuous helical geometry maximizes the heat transfer surface area within the tower's confined volume, achieving higher thermal efficiency compared to plate-fin or straight-tube alternatives.
Additional Applications
- Industrial Process Cooling: Chemical reactors, polymerization processes, and pharmaceutical manufacturing requiring closed-loop thermal management.
- Food & Beverage Processing: Pasteurization heat exchangers and condensate recovery systems where hygienic, corrosion-resistant surfaces are mandatory.
- Power Generation: Condenser tubes and cooling coil assemblies in combined-cycle and nuclear power plants.
- HVAC Systems: Chilled water coil assemblies in commercial and industrial air handling units.
- Marine & Offshore: Sea-water cooling coils for shipboard and platform equipment, leveraging the chloride resistance of 316L grade.
- Waste Heat Recovery: Exhaust gas heat recovery coils in industrial furnaces and kilns.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management Systems certification, covering all aspects of production, inspection, and customer service.
- ISO 14001:2015 — Environmental Management Systems certification, demonstrating commitment to sustainable manufacturing practices.
- CE Marking — Conformity with European directives for pressure equipment (PED 2014/68/EU) where applicable.
- EN 10204 3.1 — Third-party inspection certificates available upon request, confirming material certification by an independent inspection body.
- ASTM / ASME Material Certification — Each heat lot is accompanied by a full material test certificate (MTC) documenting chemical composition, mechanical properties, and heat treatment records.
- NACE MR0175 / ISO 15156 — Compliance available for 316L grade coils intended for sour service (H₂S-containing environments).
Unique Selling Points
Research-Validated Thermal Performance: The coiltube design parameters — including coil pitch, tube diameter, and surface finish — have been validated through rigorous experimental and computational fluid dynamics (CFD) studies on evaporative cooling coil tube heat and mass transfer performance. This ensures that the product delivers predictable, optimized thermal output across varying load and environmental conditions.
- Seamless Continuous Coil Construction: The elimination of field-welded joints significantly reduces the risk of corrosion-induced failure and leak development, extending service life and reducing maintenance frequency.
- Optimized Coil Geometry: Helical coil configurations with precisely controlled pitch and bend radius maximize the convective heat transfer coefficient while maintaining acceptable pressure drop, achieving an optimal balance between thermal efficiency and pumping energy consumption.
- Superior Corrosion Resistance: The austenitic stainless steel composition, combined with post-manufacturing pickling and passivation, provides exceptional resistance to the chemically aggressive environment of cooling tower water containing dissolved salts, chlorides, and biological contaminants.
- Full Traceability: Every coil tube carries a unique heat lot identification, enabling complete traceability from raw material mill certificate through final product delivery — a critical requirement for regulated industries such as pharmaceuticals, food processing, and nuclear power.
- Custom Engineering Capability: Wenzhou Jixing Metal Materials offers full customization of coil diameter, pitch, tube dimensions, end fittings, and surface finish to meet specific project requirements, supported by engineering consultation and thermal performance simulation services.
Technical Notes
When specifying this coiltube for evaporative cooling tower applications, engineers should consider the following factors for optimal system design:
- The coil pitch-to-diameter ratio (P/D) directly influences the air-side heat transfer coefficient; a P/D ratio of 1.5–2.5 is generally optimal for evaporative cooling applications.
- Surface roughness (Ra) below 0.8 μm is recommended to minimize fouling and biofilm accumulation in cooling water service.
- For applications involving high-chloride cooling water (e.g., seawater-cooled towers), 316L grade is strongly recommended over 304 to prevent chloride stress corrosion cracking (CSCC) at temperatures above 60°C.
- Support brackets should be installed at intervals not exceeding 1.5 m to prevent coil sagging and vibration-induced fatigue under continuous operation.