Stainless Steel Coil Tube — Valve Cooling System Cooling Tower Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for high-performance thermal management applications in High Voltage Direct Current (HVDC) converter stations. This coil tube serves as a critical heat exchange component within the valve cooling system cooling tower, where it facilitates efficient heat dissipation from converter valves while maintaining structural integrity under continuous cyclic thermal and hydraulic loading conditions.
The product is engineered to address the persistent challenge of scale formation (fouling) in cooling tower systems, supporting the integration of automated descaling electric actuator assemblies. The coil tube's geometry, material composition, and surface finish are optimized to minimize mineral deposition, prolong service intervals, and ensure reliable thermal performance throughout the operational lifespan of the converter station cooling infrastructure.
2. Material & Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their exceptional combination of corrosion resistance, thermal conductivity, and mechanical durability in aggressive cooling tower environments.
- Primary Grade: AISI 316L (UNS S31603) — low-carbon variant offering superior resistance to pitting and crevice corrosion caused by chloride ions present in cooling tower water
- Alternative Grade: AISI 304L (UNS S30403) — standard austenitic grade suitable for moderate chloride environments
- Specialty Grade: AISI 316Ti (UNS S31609) — titanium-stabilized variant providing enhanced resistance to intergranular corrosion during welding operations
Key Material Properties
- Corrosion Resistance: Excellent resistance to cooling tower water containing chlorides, sulfates, and dissolved oxygen; Linear Polarization Resistance (LPR) > 100 mV in 3.5% NaCl solution
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, providing efficient heat transfer capability
- Mechanical Strength: Yield strength (0.2% offset) ≥ 170 MPa; Tensile strength ≥ 485 MPa
- Temperature Range: Continuous service from −196°C to +400°C without loss of mechanical properties
- Surface Finish: Electropolished or passivated finish with surface roughness Ra ≤ 0.4 μm to inhibit scale adhesion
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 19 mm – 159 mm (customizable) | GB/T 14976, ASTM A269 |
| Wall Thickness | 0.8 mm – 6.0 mm | GB/T 14976, EN 10217 |
| Coil Bend Radius | 50 mm – 500 mm (minimum) | Internal design specification |
| Coil Length | Up to 30 m per continuous coil | Manufacturing capability |
| Surface Roughness (Ra) | ≤ 0.4 μm (electropolished) | ASTM A967 |
| Pressure Rating | Up to 1.6 MPa (PN16) | GB/T 150, ASME B31.3 |
| Working Temperature | −196°C to +400°C | Material specification |
| End Condition | Plain end, beveled end, or pre-flanged | Customer requirement |
| Heat Treatment | Solution annealed and water quenched | GB/T 12451 |
| Passivation Treatment | ASTM A967 citric acid or nitric acid passivation | ASTM A967 |
| Dimensional Tolerance | ±0.1 mm (OD); ±0.05 mm (wall thickness) | GB/T 14976 Class A |
| Material Certification | Mill test certificate (MTC) per EN 10204 Type 3.1 | EN 10204 |
4. Manufacturing Process
The production of high-precision stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence ensuring dimensional accuracy, metallurgical quality, and surface integrity:
- Raw Material Selection: Virgin stainless steel coil stock procured from certified mills with full chemical composition verification via Optical Emission Spectroscopy (OES) and Carbon-Sulfur (C/S) analyzer testing.
- Precision Cold Drawing: Seamless or welded tube blanks are cold-drawn through calibrated tungsten carbide die sets to achieve exact outer diameter and wall thickness tolerances while inducing beneficial work hardening for enhanced mechanical strength.
- Coil Forming (Cold Bending): The straight tube is mechanically coiled using CNC-controlled spiral winding machinery with integrated roller guide systems to achieve consistent bend radius without wall thinning, ovality, or residual stress concentrations. The minimum bend radius is maintained at 5D (five times the outer diameter) to prevent cross-sectional distortion.
- Welding (if applicable): Orbital TIG (Tungsten Inert Gas) welding is employed for joining coil ends or integrating with header manifolds. Weld parameters are optimized for full-penetration single-pass welds with argon back-purging to prevent internal oxidation.
- Solution Annealing: Tubes are solution annealed at 1050°C ± 20°C followed by rapid water quenching to restore full austenitic microstructure, eliminate residual stresses from cold forming, and maximize corrosion resistance.
- Surface Finishing: Electropolishing or chemical passivation removes surface contaminants, dissolved iron, and oxide layers, creating a chemically stable chromium-rich passive film essential for long-term corrosion protection in cooling tower water.
- Quality Inspection: Final inspection includes dimensional measurement (caliper, micrometer), hydrostatic pressure testing, visual inspection of welds and surfaces, and material verification via Positive Material Identification (PMI) using X-ray Fluorescence (XRF) spectroscopy.
5. Applications
This stainless steel coil tube is purpose-engineered for demanding industrial thermal management applications:
- HVDC Converter Station Valve Cooling Systems: Primary application — serves as the heat exchange element in cooling tower coil assemblies where converter valve heat is transferred to circulating cooling water. The coil geometry maximizes heat transfer surface area within a compact footprint.
- Cooling Tower Coil Assemblies: Installed within forced-draft or induced-draft cooling towers as part of the descaling-capable cooling circuit, compatible with automated electric actuator-driven descaling mechanisms.
- Power Plant Condenser Systems: Secondary application in thermal power generation facilities requiring high-integrity heat exchanger tubing resistant to thermal cycling.
- Chemical Processing Heat Exchangers: Suitable for heat exchange applications involving aggressive process fluids where austenitic stainless steel corrosion resistance is required.
- Industrial Refrigeration Systems: Application in ammonia or fluorocarbon refrigerant circuits where cryogenic temperature resistance is essential.
Unique Selling Points
- Descaling-Compatible Design: Coil geometry and surface finish specifically engineered to minimize scale adhesion, enabling effective operation with automated electric actuator-driven descaling systems and significantly extending maintenance intervals.
- Converter Station Grade: Manufactured to specifications validated for HVDC converter station valve cooling service, where reliability is mission-critical and downtime is prohibitively costly.
- Superior Surface Finish: Electropolished Ra ≤ 0.4 μm surface provides a hydrodynamic advantage that reduces fouling rates by up to 60% compared to standard mill finish tubing.
- Full Traceability: Complete material traceability from mill certificate through final inspection, with EN 10204 Type 3.1 certification ensuring compliance with international power infrastructure procurement standards.
- Custom Coil Configuration: Flexible manufacturing capability supporting custom coil diameters, lengths, and end configurations to match specific cooling tower and valve cooling system design requirements.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity with international standards:
- ISO 9001:2015 — Quality Management System certification demonstrating systematic control of manufacturing processes
- ISO 14001:2015 — Environmental Management System certification ensuring environmentally responsible production practices
- GB/T 14976 — Chinese national standard for stainless steel seamless tubes for general engineering purposes
- ASTM A269 / A270 — American material standards for austenitic stainless steel seamless, welded, and heavily cold-worked tubes
- EN 10217-7 — European standard for austenitic stainless steel seamless and welded tubes for pressure purposes
- GB/T 12451 — Chinese national standard for heat treatment specifications of stainless steel tubes
- EN 10204 Type 3.1 — Inspection document certification providing independent verification of product conformity
- ASME Section IX — Welding qualification procedures for pressure-containing components (where applicable)
Note: This product specification is intended for engineering reference and procurement evaluation. All dimensional tolerances, mechanical properties, and material certifications are subject to verification against the specific purchase order and applicable project specifications. Custom configurations should be discussed with the manufacturer's engineering team for feasibility assessment and lead time confirmation.