Stainless Steel Coil Tube (Coil Tube) — Industrial Water Heat Exchanger Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Reference No.: 1550
Classification: Literature Study / Technical Reference
Product Overview
The Stainless Steel Coil Tube (盘管式Coil Tube) is a precision-engineered continuous tubular product manufactured in a coiled configuration, designed for use in industrial water heat exchange systems, cooling coils, and cathodic protection applications. Unlike discrete pipe sections, coil tubes are formed as uninterrupted lengths wound into helical or spiral configurations, enabling efficient integration into shell-and-coil heat exchangers, evaporator assemblies, and process water circulation systems.
This product line draws upon extensive research into cathodic protection potential distribution in industrial water coil equipment (《工业水中盘管式设备阴极保护电位分布研究》), ensuring that the coil tube geometry, material selection, and surface finish are optimized for corrosion resistance under submerged and semi-submerged industrial water conditions. The coiled geometry provides superior thermal transfer efficiency while minimizing pressure drop compared to straight-pipe equivalents of equivalent surface area.
Material & Properties
Base Materials
- Austenitic Stainless Steels: SUS304 (1.4301), SUS316L (1.4404) — offering excellent general corrosion resistance and weldability.
- Duplex Stainless Steels: SUS316L Mo-enriched grades for aggressive chloride-containing industrial water environments.
- Super-Austenitic Grades: Available for high-chloride, high-temperature service where cathodic protection potential shifts may accelerate localized corrosion.
Key Mechanical & Physical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (304), ≥ 550 MPa (316L) | ASTM A213 / GB/T 12771 |
| Yield Strength (Rp0.2) | ≥ 205 MPa (304), ≥ 220 MPa (316L) | ASTM A213 / GB/T 12771 |
| Elongation (A50) | ≥ 40% | ASTM A213 |
| Hardness (HBW) | ≤ 220 | ISO 6508 |
| Corrosion Resistance (Pitting) | PIT ≥ 24 (304), PIT ≥ 30 (316L) | ASTM G48 Method B |
| Crevice Corrosion Resistance | Qualified at ≤ 60°C in 3% NaCl | ASTM G48 Method C |
| Maximum Service Temperature | ≤ 870°C (oxidation limit) | — |
| Minimum Service Temperature | ≤ -196°C (ductility retained) | ASTM A213 |
Surface Finish Options
- Pickled & Passivated (2B): Standard finish, Ra ≤ 0.8 μm — suitable for general industrial water service.
- Mechanically Polished: Ra ≤ 0.4 μm — recommended where biofilm adhesion must be minimized.
- Electropolished: Ra ≤ 0.2 μm — for high-purity or cathodic protection-critical applications where surface integrity directly influences potential distribution uniformity.
Specifications
| Parameter | Range / Value | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ 6.0 mm – Φ 50.8 mm (1/4" – 2") | ASTM A213 / GB/T 12771 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A213 |
| Coil Diameter (Bundle) | Φ 100 mm – Φ 500 mm | Custom / OEM |
| Coil Pitch (Spacing) | 5 mm – 25 mm (adjustable) | Custom / OEM |
| Tube Length per Coil | 10 m – 200 m (continuous) | — |
| Coil Turns | Up to 200 turns per assembly | — |
| Pressure Rating | Up to 2.5 MPa (design), tested at 3.75 MPa | ASME BPV Code |
| Temperature Rating | -40°C to +250°C (standard); up to +400°C (special order) | — |
| Tolerance — OD | ±0.1 mm (≤ Φ 12.7 mm); ±0.15 mm (> Φ 12.7 mm) | ASTM A213 |
| Tolerance — WT | ±10% of nominal | ASTM A213 |
| End Condition | Plain end, beveled end, or flared end | Custom |
| Heat Treatment | Solution annealed (1050–1150°C) + water quench | ASTM A213 |
| Coil Winding Tolerance | Diameter variation ≤ ±2 mm; pitch variation ≤ ±0.5 mm | Internal QA |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage process chain designed to ensure dimensional accuracy, metallurgical integrity, and corrosion performance:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to spectroscopic analysis (PMI/OES) to verify chemical composition (Cr ≥ 18%, Ni ≥ 8% for 304; Mo ≥ 2% for 316L).
- Coiling & Forming: The strip is fed through precision roll-forming dies to create the helical coil geometry. CNC-controlled winding ensures uniform coil diameter and pitch, critical for even potential distribution in cathodic protection applications.
- Welding (if applicable): Longitudinal welds, where present, are performed via Automatic Orbital TIG (Tungsten Inert Gas) welding with argon shielding (99.999% purity). Weld parameters are optimized to prevent intergranular sensitization in the heat-affected zone (HAZ).
- Solution Annealing: Coils are heat-treated at 1050–1150°C followed by rapid quenching to dissolve carbide precipitates and restore full austenitic corrosion resistance.
- Pickling & Passivation: Immersion in mixed acid baths (HNO3/HF) removes scale and surface contaminants, followed by passivation treatment to establish a stable chromium oxide passive film.
- Dimensional Verification: Laser scanning and ultrasonic thickness gauging confirm OD, WT, coil diameter, and pitch compliance with tolerance specifications.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× design pressure for a minimum hold time of 30 minutes, with no visible leakage or deformation permitted.
- Final Inspection & Packaging: Visual inspection, surface roughness measurement, and cathodic protection compatibility assessment (potential distribution mapping) are performed prior to protective packaging.
Cathodic Protection Compatibility
Key Research Insight: Based on the study "Cathodic Protection Potential Distribution in Industrial Water Coil Equipment," the helical coil geometry creates non-uniform potential fields when subjected to impressed-current or sacrificial anode cathodic protection systems. The inner turns of the coil experience reduced cathodic protection effectiveness due to geometric shielding effects. Wenzhou Jixing Metal Materials Co., Ltd. incorporates this research finding into design guidance, recommending:
- Optimal coil pitch ≥ 1.5× tube OD to ensure adequate electrolyte flow and potential uniformity.
- Selection of 316L or duplex grades for installations where cathodic protection potentials may shift below -0.85 V (vs. Cu/CuSO4) in chloride-rich environments.
- Periodic potential mapping at 25% intervals along the coil length during commissioning and annual inspection.
Applications
- Industrial Water Heat Exchangers: Shell-and-coil configurations for process cooling, boiler feedwater preheating, and thermal recovery systems.
- Evaporators & Distillation Systems: Multi-effect evaporators in chemical, pharmaceutical, and food processing industries.
- Marine & Offshore Systems: Seawater cooling coils with cathodic protection integration for platform cooling loops.
- Power Generation: Condenser coils and feedwater heater elements in thermal and nuclear power plants.
- Chemical Processing: Reactor cooling coils and heat recovery exchangers handling corrosive process streams.
- Water Treatment Plants: Cooling coils for RO concentrate recirculation and thermal desalination systems.
- HVAC & Refrigeration: Chilled water coils and condenser tubes for commercial and industrial climate control.
Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing operations |
| ISO 14001:2015 | Environmental Management System compliance |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| EN 10204 Type 3.1 | Inspection Certificate issued by authorized quality representative |
| CE Marking | Compliance with EU Pressure Equipment Directive (PED 2014/68/EU) |
| ASME "S" Stamp | Sectional stamp for process piping (where applicable) |
| NACE MR0175 / ISO 15156 | Resistance to sulfide stress cracking for sour service |
| ASTM A213 | Standard specification for seamless austenitic stainless steel tubes |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes |
| GB/T 14976 | Chinese national standard for cold-rolled stainless steel tubes |
Unique Selling Points
- Research-Backed Design: Product development informed by published academic research on cathodic protection potential distribution in coil geometries, providing customers with evidence-based design recommendations.
- Continuous Length Advantage: Seamless coiled production eliminates butt-weld joints, reducing leak points and maintenance requirements by up to 90% compared to discrete pipe assemblies.
- Geometric Precision: CNC-controlled winding achieves coil diameter tolerances within ±2 mm, ensuring uniform flow distribution and predictable thermal performance.
- Full Traceability: Each coil batch carries a unique heat number with complete material traceability from mill certificate through final inspection, supporting lifecycle asset management.
- Custom Engineering Support: Wenzhou Jixing Metal Materials Co., Ltd. provides coil geometry optimization services based on thermal load calculations, flow regime analysis, and cathodic protection system design parameters.
- Corrosion Performance Validation: Electropolished finish options combined with 316L/duplex material availability provide verified resistance in aggressive industrial water environments containing chlorides, sulfides, and dissolved oxygen.
Technical Documentation Provided
- Material Test Certificate (MTC) — EN 10204 3.1
- Heat Treatment Record & Annealing Log
- Pressure Test Report (hydrostatic)
- Cathodic Protection Compatibility Assessment (upon request)
- Coil Geometry Dimensional Report (laser scan data)
- Surface Finish Measurement Report (Ra values)
- Installation & Commissioning Guide
- Maintenance & Inspection Schedule (including potential mapping intervals)