Stainless Steel Coil Tube for Ultra-High Temperature (UHT) Sterilization Systems
Product No. 634 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Stainless Steel Coil Tube (盘管) is a precision-engineered coiled tubular component designed for use in Ultra-High Temperature (UHT) sterilization systems, particularly those employed in the food and beverage processing industry. This product is specifically engineered to meet the rigorous thermal, mechanical, and hygienic demands of Tetra Pak coil-type UHT sterilizers and scraped-film UHT sterilizers. The coil tube serves as the core heat-exchange element, facilitating rapid and uniform thermal processing of liquid food products such as milk, juice, and dairy derivatives.
Unlike conventional straight-tube heat exchangers, the coiled geometry provides an extended surface area within a compact footprint, enabling efficient heat transfer while maintaining low pressure drop across the system. The spiral configuration also promotes secondary flow patterns within the tube, enhancing turbulent mixing and reducing the risk of thermal degradation or scorching of product on the tube wall.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to the following specifications:
- ASTM A312 / ASME SA-312 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Heat-Transfer and General Heat-Exchange Service
- AISI 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- AISI 316L (UNS S31603) — Low-carbon, molybdenum-bearing austenitic stainless steel for enhanced resistance to pitting and crevice corrosion
- EN 10217-7 — European standard for austenitic stainless steel tubes for pressure purposes
2.2 Key Mechanical and Physical Properties
| Property | AISI 304 (UNS S30400) | AISI 316L (UNS S31603) |
|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 485 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa |
| Elongation (A5) | ≥ 40% | ≥ 40% |
| Density (20°C) | 8.00 g/cm³ | 8.03 g/cm³ |
| Thermal Conductivity (50°C) | 16.3 W/(m·K) | 16.3 W/(m·K) |
| Thermal Conductivity (300°C) | 21.6 W/(m·K) | 22.7 W/(m·K) |
| Linear Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ /K | 16.6 × 10⁻⁶ /K |
| Chromium (Cr) Content | 18.0 – 20.0% | 16.0 – 18.0% |
| Nickel (Ni) Content | 8.0 – 10.5% | 10.0 – 14.0% |
| Molybdenum (Mo) Content | — | 2.0 – 3.0% |
| Carbon (C) Maximum | 0.08% | 0.03% |
2.3 Corrosion Resistance
Both AISI 304 and AISI 316L exhibit excellent resistance to oxidation and general corrosion in food-grade environments. The molybdenum addition in 316L provides superior resistance to chloride-induced pitting corrosion, making it particularly suitable for UHT applications involving salt-containing media or aggressive CIP (Clean-In-Place) cleaning agents such as caustic soda (NaOH) and nitric acid (HNO₃) solutions.
2.4 Surface Finish
- Internal Surface: Electro-polished or mechanically polished to achieve a surface roughness of Ra ≤ 0.4 μm (hygienic grade), ensuring minimal product adhesion and facilitating CIP cleaning
- External Surface: Mill finish or pickled-and-passivated finish, Ra ≤ 1.6 μm
- Passivation: Nitric acid passivation per ASTM A967 or ASTM A380 to establish a stable chromium oxide protective layer
3. Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (盘管Coiltube) — Ref. No. 634 |
| Tube Outer Diameter (OD) | 6.0 mm / 8.0 mm / 10.0 mm / 12.0 mm / 14.0 mm / 16.0 mm (customizable) |
| Wall Thickness (t) | 0.5 mm – 2.0 mm |
| Coil Inner Diameter (D) | 25 mm – 200 mm (depending on application geometry) |
| Coil Length (L) | Up to 2,000 m continuous coil (custom lengths available) |
| Coil Pitch (p) | 1.2 × OD to 2.5 × OD (optimized for heat transfer efficiency) |
| Operating Temperature Range | -200°C to +870°C (continuous); UHT peak: 135–150°C |
| Operating Pressure | Up to 2.0 MPa (gauge); design pressure up to 3.0 MPa |
| Helix Angle | 10° – 30° (adjustable for flow characteristics) |
| End Connections | Welded (TIG/Orbital), flanged, or sanitary tri-clamp fittings |
| Applicable Standards | ASTM A312, ASME SA-312, EN 10217-7, GB/T 13296 |
| Food-Grade Compliance | 3-A Sanitary Standards, FDA 21 CFR 178.301, EU 1935/2004 |
| Heat Transfer Coefficient (U) | 800 – 1,500 W/(m²·K) (depending on flow regime and media) |
| Pressure Drop (ΔP) | 0.05 – 0.3 MPa (at nominal flow velocity of 2–4 m/s) |
4. Manufacturing Process
4.1 Material Preparation
Raw material is sourced as cold-drawn seamless stainless steel tube, conforming to ASTM A312 / ASME SA-312. Incoming material undergoes rigorous inspection including spectroscopic chemical analysis (OES — Optical Emission Spectroscopy), dimensional verification, and visual examination for surface defects.
4.2 Coil Forming
The coil forming process employs high-precision CNC-controlled coiling machines capable of producing consistent helical geometries with tight dimensional tolerances. The process involves:
- Straightening: The incoming tube is passed through a straightening mill to ensure uniform straightness (≤ 0.5 mm/m deviation)
- Heating (if required): For larger diameters or thicker walls, the tube may be locally heated to 200–400°C to reduce forming resistance and prevent work hardening
- Helical Coiling: The tube is guided through precision-forming rollers that impart a uniform helical curvature. The coil pitch and diameter are controlled to ±0.5 mm tolerance
- Springback Compensation: The forming machine incorporates springback compensation algorithms to ensure dimensional accuracy after elastic recovery
4.3 Post-Forming Treatment
- Solution Annealing: For coils exhibiting excessive work hardening, solution annealing at 1050–1100°C followed by rapid quenching (air or water) restores full austenitic structure and ductility
- Pickling: Immersion in a mixed acid bath (HNO₃/HF or HNO₃/HCl) to remove oxide scale and surface contaminants
- Passivation: Final treatment with dilute nitric acid (10–20% HNO₃) to regenerate the passive chromium oxide film
- Electro-polishing (EP): For hygienic internal surfaces, electro-polishing is performed at 50–60°C in a phosphoric acid/electrolyte solution to achieve Ra ≤ 0.4 μm
4.4 End Processing and Assembly
Coin ends are prepared according to the specific application requirements: orbital TIG welding for seamless joints, hydraulic expansion for tube-to-header connections, or mechanical sanitary fittings (Tri-Clamp, Dimple-Grip) for easy disassembly and cleaning.
4.5 Quality Control
- Dimensional Inspection: OD, wall thickness, coil diameter, and pitch verified via laser scanning and CMM (Coordinate Measuring Machine)
- Non-Destructive Testing (NDT): Eddy current testing (ECT) per ASTM E309 for wall thickness mapping; penetrant testing (PT) per ASTM E165 for surface crack detection
- Pressure Testing: Hydrostatic testing at 1.5× design pressure per ASME B31.3
- Surface Metrology: Surface roughness measurement per ISO 4287; profilometer verification
- Chemical Analysis: Confirmation of alloy composition via OES or PMI (Positive Material Identification)
5. Applications
5.1 UHT Sterilization Systems
The primary application of this stainless steel coil tube is within Ultra-High Temperature (UHT) sterilization equipment used in the food and beverage industry. Key application areas include:
- Tetra Pak Coil-Type UHT Sterilizers: The coil tube serves as the heating and holding tube, where the product is rapidly heated to 135–150°C and held for 2–5 seconds to achieve commercial sterility (12-log reduction of Clostridium botulinum spores)
- Tetra Pak Scraped-Film UHT Sterilizers: The coil tube functions as a heat-exchange surface in the pre-heating and cooling sections, with a rotating scraper assembly preventing product contact time exceeding 1 second on the tube wall
- Plate Heat Exchanger (PHE) Alternative: In applications where fouling resistance is critical, the coil tube offers superior cleaning characteristics compared to plate-and-frame designs
5.2 Other Industrial Applications
- Pharmaceutical Sterilization: Terminal sterilization of pharmaceutical solutions and parenteral products
- Cosmetics Processing: UHT treatment of liquid cosmetic formulations requiring extended shelf-life
- Chemical Heat Exchangers: Corrosion-resistant heat exchange in aggressive chemical environments
- Energy Sector: Solar thermal collector coils and heat recovery systems
- Refrigeration: Evaporator and condenser coils in industrial refrigeration systems
6. Quality Certifications & Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — Design, Manufacturing, and Supply |
| ISO 22000 / HACCP | Food Safety Management System — Food-Grade Equipment Components |
| 3-A Sanitary Standards (ANSI/3-A) | Sanitary Design for Food Equipment — Surface Finish and Construction |
| ASME BPE (Bioprocessing Equipment) | Hygienic Design for Bioprocessing Applications |
| CE Marking (EU Directive 2014/68/EU) | Pressure Equipment Directive — Category I (where applicable) |
| NSF/ANSI 61 | Health Effects for Drinking Water System Components |
| FDA 21 CFR 178.301 | Food Contact Materials — Stainless Steel Compliance |
| EU Regulation 1935/2004 | Framework Regulation on Materials and Articles in Contact with Food |
| GB/T 13296 (China National Standard) | Stainless Steel Tubes for General and Heat-Exchange Purposes |
| EN 10217-7 | Austenitic Stainless Steel Tubes for Pressure Purposes |
7. Unique Selling Points
- Superior Heat Transfer Efficiency: The helical coil geometry induces Dean vortices within the tube, promoting turbulent flow even at lower Reynolds numbers (Re > 2,300), thereby enhancing convective heat transfer coefficients by 20–40% compared to straight tubes of equivalent length.
- Compact Footprint: The coiled design achieves 3–5× the heat transfer surface area per unit volume compared to straight-tube configurations, enabling significant space savings in process plant layout.
- Low Fouling Tendency: Secondary flow patterns within the coil prevent boundary layer stagnation, reducing product deposition and fouling accumulation on the tube wall.