316L Sanitary Heat-Exchange Coil Tube for Dairy Pasteurizers

Product Overview

The 316L sanitary heat-exchange coil tube (Coiltube) is a precision-engineered stainless steel tubing product specifically designed for use in pasteurizer heat-exchange systems within the dairy processing industry. This coil tube serves as the critical thermal transfer medium in pasteurization units, where raw milk is subjected to controlled thermal treatment at temperatures between 72–85°C for a minimum of 15 seconds to achieve pathogen elimination while preserving nutritional and organoleptic properties.

The product addresses one of the most persistent operational challenges in dairy pasteurization — protein fouling and scaling — caused by the thermal denaturation and adhesion of milk proteins (particularly whey proteins and casein micelles) onto the inner tube surface during sustained heating. Through advanced material selection, surface engineering, and hydrodynamic design optimization, this coil tube significantly extends cleaning intervals (CIP cycles), reduces energy consumption, and ensures consistent thermal processing performance over extended operational lifecycles.

Material & Properties

The coil tube is fabricated from ASTM A270 / AMS 5663 Grade 316L (UNS S31603) austenitic stainless steel, the industry-preferred alloy for sanitary food processing applications. The addition of 2.0–3.0% molybdenum provides superior resistance to chloride-induced pitting and crevice corrosion, which is critical in environments where milk residues, cleaning agents (caustic soda, nitric acid), and condensate may accumulate.

Specifications

Parameter Specification Standard / Reference
Material Grade 316L (UNS S31603) Austenitic Stainless Steel ASTM A270 / AMS 5663
Tube Type Sanitary Seamless Coil Tube —
Outer Diameter (OD) 12.7 mm (½") – 25.4 mm (1") — customizable ASTM A554 / ASME B36.19M
Wall Thickness 0.8 – 1.6 mm (tolerance ±10%) —
Coil Winding Diameter 300 – 1200 mm (configurable per heat exchanger design) —
Surface Roughness (Ra) ≤ 0.8 μm (inner surface); ≤ 0.4 μm available on request ASTM A269 / ISO 16232
Surface Finish Electro-polished / Passivated sanitary finish ASTM A967
Operating Temperature Up to 85°C (pasteurization); design margin to 120°C —
Operating Pressure Up to 1.0 MPa (10 bar) ASME B31.3
Hydrodynamic Design Turbulent flow profile (Reynolds number > 10,000) to inhibit fouling —
End Treatment Flat-cut, deburred; sanitary tri-clamp or welded fittings compatible 3-A Sanitary Standards
Coating / Passivation Acid pickling and passivation per ASTM A967 ASTM A967
Food Safety Certification 3-A Sanitary, FDA 21 CFR compliant, EC 1935/2004 —

Manufacturing Process

The production of this sanitary heat-exchange coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, surface integrity, and metallurgical purity:

  1. Material Selection & Incoming Inspection: 316L seamless tube stock is procured from certified mill sources with full chemical and mechanical test documentation. Each batch undergoes spectral analysis (PMI) for alloy verification and visual inspection for surface defects.
  2. Cold Drawing & Precision Sizing: Tubes are cold-drawn to precise OD and wall thickness tolerances, ensuring uniformity critical for consistent heat transfer performance throughout the coil length.
  3. Coil Winding (Coiling): Tubes are mechanically wound around precision mandrels to produce the required coil geometry. The winding process is controlled to avoid work-hardening, kinking, or ovality exceeding 1% of OD.
  4. Electro-Polishing: The inner tube surface is electro-polished to achieve a surface roughness of Ra ≤ 0.8 μm. This process removes the cold-worked surface layer, eliminates micro-voids and pits, and creates a smooth, non-porous surface that resists protein adhesion. The electro-polishing process simultaneously deposits a chromium-enriched passive oxide layer.
  5. Acid Pickling & Passivation: Post-polishing treatment per ASTM A967 using a citric acid or nitric acid-based passivation solution to remove free iron contamination and restore the protective chromium oxide film. The resulting passive layer provides long-term corrosion resistance.
  6. Hydrodynamic Optimization: The coil geometry and internal surface characteristics are engineered to promote turbulent flow conditions (Reynolds number > 10,000 at design flow velocities of 1.5–3.0 m/s). Turbulent flow continuously disrupts the boundary layer where protein deposition initiates, thereby delaying fouling onset and maintaining stable thermal transfer coefficients.
  7. Final Inspection & Testing: Each coil assembly undergoes hydrostatic pressure testing (1.5× design pressure), dimensional verification, surface roughness measurement (per ISO 16232), and visual inspection under magnification for surface defects.

Applications

This 316L sanitary heat-exchange coil tube is purpose-engineered for the following dairy processing applications:

Quality Certifications & Compliance

Products manufactured by Wenzhou Jixing Metal Materials Co., Ltd. conform to the following international standards and regulatory frameworks:

Unique Selling Points

Technical Note: In dairy pasteurization systems, protein fouling represents a critical operational concern. Milk proteins undergo thermal denaturation above 65°C, leading to aggregation and adhesion onto heated surfaces. The combination of a Ra ≤ 0.8 μm electro-polished surface and turbulent flow hydrodynamics in this coil tube design directly addresses this challenge, maintaining stable U-values (overall heat transfer coefficients) and reducing total cost of ownership through extended cleaning intervals and lower energy consumption.