Stainless Steel Coil Tube — UHT Sterilization Coil (Coiltube)
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component specifically designed for integration into Ultra-High Temperature (UHT) sterilization systems used in the food processing and dairy industries. This coiled tube assembly serves as the core heat exchange and sterilization element within coiled-type sterilizers, enabling rapid, uniform, and hygienic thermal processing of liquid food products such as milk, juice, and plant-based beverages.
Coiled sterilization technology represents a significant advancement over traditional plate heat exchangers and tubular sterilizers in UHT processing. The continuous helical coil design eliminates dead zones, minimizes product hold-up volume, and ensures consistent residence time distribution — critical parameters for achieving complete microbial inactivation while preserving the sensory and nutritional quality of the product.
Key Insight: Research documented in "The Superiority of Coiled Sterilizers in UHT Milk Processing" demonstrates that coiled sterilizers achieve more uniform temperature profiles with narrower residence time distributions (RTD) compared to conventional sterilization equipment, resulting in superior product quality and reduced energy consumption.
2. Material & Properties
2.1 Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel conforming to international standards. The primary alloy grades utilized include:
- SUS304 / AISI 304 / EN 1.4301 — General-purpose corrosion-resistant grade with excellent weldability, suitable for food-grade sterilization applications involving non-chlorinated liquid media.
- SUS316L / AISI 316L / EN 1.4404 — Enhanced corrosion resistance grade with molybdenum addition (2.0–2.5%), recommended for applications involving higher chloride concentrations or aggressive cleaning agents.
2.2 Mechanical & Physical Properties
| Property | SUS304 (1.4301) | SUS316L (1.4404) |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 480 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa |
| Elongation (A50) | ≥ 40% | ≥ 45% |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | 16.3 W/(m·K) |
| Maximum Operating Temperature | 870°C (oxidizing) | 870°C (oxidizing) |
| Corrosion Resistance (pitting) | Good | Excellent |
2.3 Surface Finish & Hygienic Properties
- Internal Surface Roughness: Ra ≤ 0.4 μm (electropolished) — meets 3-A Sanitary Standards for dairy and food processing applications.
- External Surface Finish: 2B or BA (Bright Annealed) finish, Ra ≤ 0.5 μm.
- Wall Thickness Tolerance: ±10% of nominal value, ensuring consistent thermal performance and structural integrity.
- Chromium Oxide Passive Layer: Naturally formed Cr₂O₃ passivation layer provides inherent corrosion resistance without additional coatings.
3. Technical Specifications
| Specification Parameter | Typical Value / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 12 mm – 51 mm | ISO 3506 |
| Wall Thickness | 0.5 mm – 2.0 mm | ASTM A269 / A270 |
| Coil Diameter | 50 mm – 500 mm (customizable) | — |
| Coil Length | Up to 100 m (continuous coil) | — |
| Operating Pressure | 0.1 MPa – 1.6 MPa (design pressure) | EN 10204 |
| Operating Temperature Range | -20°C to +140°C (sustained) | — |
| UHT Sterilization Temperature | 135°C – 150°C | — |
| Heat Transfer Coefficient (U) | 800 – 1,500 W/(m²·K) | — |
| Welding Method | Orbital TIG (GTAW) — automatic | ASME BPV Section IX |
| End Connection Types | Tri-Clamp, Sanitary Threaded, Flanged | 3-A / EHEDG |
| Material Certification | EN 10204 Type 3.1 | EN 10204 |
4. Manufacturing Process
4.1 Raw Material Selection & Incoming Inspection
Raw stainless steel tubing is procured from certified mills (e.g., Outokumpu, ThyssenKrupp, or equivalent) with full chemical composition analysis and mechanical property verification per EN 10204 Type 3.1 certification. Each batch undergoes incoming inspection including visual examination, dimensional verification, and spectroscopic composition analysis (PMI — Positive Material Identification).
4.2 Tube Forming & Coil Winding
- Cutting & Deburring: Tubes are cut to required lengths using precision sawing machines, followed by automated deburring to remove all internal and external burrs.
- Coil Forming: The straight tube is wound into a precise helical coil using CNC-controlled coil winding machinery. The winding process ensures consistent pitch, diameter tolerance (±0.5 mm), and absence of kinks or deformation.
- Heat Treatment (if required): Post-forming annealing at 1050°C with water quenching may be applied to relieve residual stresses introduced during cold forming.
4.3 Welding & Assembly
All weld joints are executed using Orbital TIG (GTAW — Gas Tungsten Arc Welding) with automatic rotation, ensuring:
- Consistent weld bead geometry and penetration
- Full radiographic quality with no porosity or undercut
- Weld overlay thickness not exceeding 10% of tube wall thickness
- Post-weld internal surface roughness Ra ≤ 0.5 μm (weld ground and electropolished if required)
4.4 Surface Treatment & Passivation
- Electropolishing: Internal surface electropolishing reduces Ra to ≤ 0.4 μm, removes cold-worked surface layer, and enhances passive film formation.
- Acid Pickling & Passivation: Immersion in nitric acid (HNO₃) or citric acid solution at 60–80°C for 10–30 minutes to remove any free iron contamination and establish a stable chromium oxide passive layer.
- Final Cleaning: Purified water rinse (conductivity ≤ 10 μS/cm) and drying under controlled conditions.
4.5 Quality Control & Testing
- Dimensional Inspection: 100% measurement of OD, wall thickness, coil diameter, and pitch using CMM (Coordinate Measuring Machine) or laser scanners.
- Pressure Testing: Hydrostatic pressure test at 1.5× design pressure for minimum 30 minutes with zero leakage.
- Weld Inspection: Visual inspection per ASME BPV Section IX; 100% dye penetrant testing (PT) or radiographic testing (RT) for critical welds.
- Surface Roughness Verification: Contact profilometer measurement at multiple points along the internal surface.
- Chemical Analysis: Spectroscopic verification of alloy composition per ASTM E415.
5. Applications
5.1 UHT Milk Processing
The primary application of this coil tube is in Ultra-High Temperature (UHT) sterilization systems for liquid milk processing. The coiled sterilizer design offers distinct advantages over plate heat exchangers and tubular sterilizers:
- Elimination of Dead Zones: The continuous helical coil geometry prevents product stagnation, eliminating potential microbial growth sites that are common in plate heat exchanger channels.
- Narrow Residence Time Distribution (RTD): Achieves a more Gaussian RTD profile, ensuring that all product molecules receive consistent thermal treatment — critical for achieving a defined sterility assurance level (SAL ≤ 10⁻³).
- Low Hold-Up Volume: Reduced product inventory within the sterilizer minimizes waste during start-up, shutdown, and CIP (Clean-in-Place) cycles.
- Enhanced Heat Transfer Efficiency: Turbulent flow conditions within the coil (Reynolds number > 10,000) promote superior convective heat transfer, reducing energy consumption by 10–20% compared to conventional systems.
- Easy CIP & SIP Compatibility: The seamless coil design with no crevices or gaskets facilitates complete Clean-in-Place (CIP) and Steam-in-Place (SIP) sanitation.
- Reduced Product Degradation: Shorter, more uniform residence times at sterilization temperature minimize Maillard reactions and protein denaturation, preserving the "fresh" taste profile of UHT milk.
5.2 Additional Applications
- Plant-based beverage sterilization (soy milk, oat milk, almond milk)
- Fruit juice and nectar UHT processing
- Pharmaceutical and biotechnology liquid sterilization
- Chemical process heat exchange in corrosive environments
- Waste heat recovery systems
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| EN 10204 Type 3.1 | Material test certificate with full chemical and mechanical data |
| ISO 9001:2015 | Quality Management System certification |
| 3-A Sanitary Standards | Sanitary design for dairy and food processing equipment |
| EHEDG Guidelines | European Hygienic Engineering & Design Group compliance |
| NSF/ANSI 61 | Public Health Standard for Drinking Water System Components |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance (where applicable) |
| ASME BPV Section VIII | Pressure vessel and component construction standards |
| ISO 14532 | Hygienic design requirements for food processing equipment |
7. Unique Selling Points
- Superior Sterilization Performance: The coiled design achieves a more uniform temperature profile with reduced thermal gradients, directly translating to higher sterility assurance levels with lower energy input.
- Extended Equipment Lifespan: The absence of gaskets, seals, and crevices eliminates common failure points found in plate heat exchangers, reducing maintenance frequency and extending service intervals.
- Product Quality Preservation: Narrower residence time distribution minimizes over-processing, preserving heat-sensitive vitamins (B12, folate), proteins, and natural flavor compounds in the final product.
- Scalability & Customization: Coil tube configurations can be tailored to specific throughput requirements, sterilization temperatures, and product viscosities through adjustments in coil diameter, tube length, and winding pitch.
- Hygienic Design Excellence: Full compliance with 3-A, EHEDG, and ISO 14532 hygienic design principles ensures complete CIP/SIP accessibility and zero-product-contact with non-food-grade materials.
- Energy Efficiency: Enhanced turbulent flow characteristics within the coil reduce overall process energy consumption, contributing to lower operational costs and carbon footprint.
8. Conclusion
The Stainless Steel Coil Tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. represents a state-of-the-art solution for UHT sterilization applications in the food processing industry. Backed by rigorous quality control, international standard compliance, and the proven advantages of coiled sterilizer technology as documented in industry research, this product delivers exceptional performance in terms of sterilization efficacy, energy efficiency, product quality preservation, and operational reliability. It is particularly recommended for premium UHT milk processing lines where sensory quality, nutritional integrity, and regulatory compliance are paramount.