Stainless Steel Coil Tube for Marine Refrigeration Evaporators

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for use as evaporator coils in marine refrigeration systems, particularly within refrigerated fish holds aboard fishing vessels. These coil tubes are formed from seamless or welded stainless steel pipe stock into continuous helical coil configurations, serving as critical heat exchange surfaces in evaporative cooling systems where reliability, corrosion resistance, and thermal efficiency are paramount.

Unlike conventional straight-tube heat exchangers, coil tubes offer a compact volumetric footprint while maximizing surface area for heat transfer. In marine refrigeration applications, these coils are exposed to aggressive environments characterized by salt-laden air, high humidity, and frequent condensation, making stainless steel the material of choice for long-term structural integrity and hygienic compliance.

Material and Properties

Coil tubes are fabricated from austenitic stainless steel grades selected to balance corrosion resistance, mechanical strength, and thermal conductivity. The following grades are commonly employed:

• SAE 304 / UNS S30400 (18/8 Stainless Steel): The industry-standard grade offering excellent general corrosion resistance, good formability, and satisfactory performance in most refrigeration environments. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
• SAE 316L / UNS S31603 (18/10/2.5 Stainless Steel): Enhanced grade with 2.5% Molybdenum (Mo) addition, providing superior resistance to chloride-induced pitting and crevice corrosion — critical for marine and brine-exposed applications.
• SAE 321 / UNS S32100: Titanium-stabilized variant offering improved resistance to intergranular corrosion at elevated temperatures, suitable for high-duty evaporator applications.

Key physical and mechanical properties typical of the 316L grade used in marine coil tubes include:

• Thermal Conductivity (λ): 16.3 W/(m·K) at 20°C — adequate for refrigerant heat transfer with appropriate flow geometry
• Density (ρ): 8,000 kg/m³
• Yield Strength (R_eL): ≥ 205 MPa (annealed condition)
• Tensile Strength (R_m): ≥ 515 MPa
• Elongation (A₅): ≥ 40%
• Operating Temperature Range: −196°C to +315°C
• Maximum Working Pressure: Typically 1.6–2.5 MPa (gauge), depending on wall thickness and coil geometry

Technical Specifications

Parameter	Specification
Product Name	Stainless Steel Coil Tube (盘管 / Coiltube)
Material Grade	SAE 304, SAE 316L, SAE 321 (customizable)
Outer Diameter (OD)	6 mm – 25 mm (standard range)
Wall Thickness	0.5 mm – 2.0 mm (customizable)
Coil Diameter (CD)	100 mm – 600 mm (adjustable per application)
Coil Length	Up to 200 m per continuous coil
Surface Finish	No. 4 Brushed, Mirror (Ra ≤ 0.2 μm), or Matte
End Condition	Plain end, Flanged, Threaded, or Socket Weld
Heat Treatment	Solution Annealed and Pickled (Acid Passivated)
Refrigerant Compatibility	R-404A, R-407C, R-134a, R-507, Ammonia (NH₃), CO₂ (R-744)
Standard Reference	GB/T 12771, ASTM A213/A269, EN 10216-5
Application Pressure Rating	Up to 2.5 MPa (gauge)
Application Temperature Range	−40°C to +120°C (typical refrigeration duty)
Coating Options	Bare Stainless, PTFE (Teflon) Coated, or Epoxy Lined
Packaging	Wooden crate with moisture-proof wrapping and desiccant

Manufacturing Process

The production of stainless steel coil tubes involves a multi-stage process combining precision metal forming, thermal treatment, and rigorous quality control:

1. Raw Material Procurement: Seamless stainless steel pipe (per ASTM A213 TP316L) or welded pipe (per ASTM A269) is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition and mechanical testing to confirm tensile properties.
2. Coil Forming: Pipe stock is fed through a CNC-controlled coil forming machine that imparts a helical geometry. The forming process is designed to minimize work hardening and ovalization, maintaining dimensional accuracy within ±0.5 mm of nominal coil diameter. For larger coil diameters, a cold-forming or warm-forming approach is selected based on material grade and wall thickness.
3. Heat Treatment (Solution Annealing): Formed coils are subjected to solution annealing at 1,050–1,150°C followed by rapid quenching to restore the full austenitic microstructure, eliminate residual stresses, and maximize corrosion resistance. This step is critical to prevent sensitization (chromium carbide precipitation) at grain boundaries.
4. Pickling and Passivation: Annealed coils undergo acid pickling (nitric/hydrofluoric acid blend) to remove mill scale and oxidation, followed by passivation to restore the protective chromium oxide layer. This ensures the surface meets hygienic and corrosion-performance requirements.
5. Surface Finishing: Depending on application requirements, coils may receive additional surface treatment including mechanical brushing, electropolishing, or application of protective coatings (PTFE, epoxy).
6. End Preparation: Coil ends are cut to length and prepared with the specified termination type — flanged connections for bolted assembly, threaded ends for direct fitting, or plain ends for welding into a header manifold.
7. Quality Inspection: Each coil undergoes hydrostatic pressure testing (typically at 1.5× working pressure), dimensional verification, and visual inspection. For critical marine applications, dye penetrant testing (DPT) or eddy current testing may be performed to detect surface or near-surface defects.

Applications

Stainless steel coil tubes are deployed in a wide range of thermal management and fluid transfer applications, with particular emphasis on the following sectors:

• Marine Refrigeration (Fishing Vessels): Evaporator coils installed in refrigerated fish holds to maintain fish products at sub-zero temperatures (typically −18°C to −25°C). The compact coil geometry enables efficient air-side heat transfer across the hold volume while resisting corrosion from saltwater spray and high-humidity environments.
• Commercial Refrigeration: Display case evaporators, blast freezers, and cold storage room cooling systems in food processing and retail.
• Process Heat Exchange: Compact evaporators and condensers in chemical, pharmaceutical, and food processing plants where product-contact surfaces must meet sanitary standards.
• Automotive and Aerospace Thermal Management: Condenser coils and evaporator assemblies in HVAC systems.
• Heat Pump Systems: Evaporator coils in ground-source and air-source heat pump units.
• Industrial Fluid Transport: Coiled tubing for subsea wellhead connections, oil and gas production systems, and chemical dosing lines.

Unique Selling Points

• Superior Corrosion Resistance in Marine Environments: The 316L grade with Molybdenum addition provides exceptional resistance to chloride pitting and crevice corrosion, significantly extending service life in saltwater-spray and brine-exposed conditions compared to carbon steel or 304-grade alternatives.
• Optimized Heat Transfer Geometry: The helical coil configuration enhances turbulence and convective heat transfer coefficients on the refrigerant side, resulting in higher evaporator capacity per unit volume — a critical advantage in space-constrained marine installations.
• Sanitary and Hygienic Compliance: Available with mirror-polished inner surfaces (Ra ≤ 0.2 μm) and electropolished finishes, meeting FDA, 3-A, and EHEDG sanitary standards for direct food-contact applications.
• Wide Refrigerant Compatibility: Designed for compatibility with HFC, HFO, and natural refrigerants including ammonia (NH₃) and carbon dioxide (R-744), supporting the industry transition toward low-GWP refrigeration systems.
• Customizable Specifications: Wenzhou Jixing Metal Materials Co., Ltd offers flexible customization of coil diameter, pitch, tube size, wall thickness, and end connections to match specific evaporator manifold designs and installation constraints.
• Thermal Simulation-Validated Performance: Product designs are informed by computational fluid dynamics (CFD) and thermal performance simulation studies, including validated research on evaporator coil heat transfer characteristics in refrigerated fish holds, ensuring predictable and optimized thermal performance.

Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and product certification portfolio to assure customer confidence:

• ISO 9001:2015 — Quality Management System certification ensuring consistent manufacturing quality and process control.
• ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
• ASME Stamp Authorization — Where applicable, pressure-containing components are manufactured under ASME Section VIII Div. 1 or Div. 2 guidelines.
• CE Marking — Conformity with European directives including the Pressure Equipment Directive (PED 2014/68/EU) and Machinery Directive (2006/42/EC).
• Material Certification: Each batch of coil tubes is accompanied by a Mill Test Certificate (MTC) per EN 10204 Type 3.1, documenting chemical composition, mechanical properties, and heat treatment records.
• Hydrostatic Testing: All coils are pressure-tested at 1.5× the design working pressure and certified with individual test reports.
• Compliance with GB/T 12771 — Chinese national standard for welded stainless steel seamless and welded tubes, ensuring dimensional and mechanical conformity.
• Compliance with ASTM A213 / A269 — American standards for seamless and welded austenitic stainless steel tubes used in boiler, heat exchanger, and similar service.
• DNV-GL / Lloyd's Register Approval — Marine classification society approval for components intended for installation on certified vessels.

Note: All specifications listed herein represent typical values and standard configurations. Wenzhou Jixing Metal Materials Co., Ltd provides customized engineering solutions and technical consultation for specialized applications. Final product specifications should be confirmed through a formal technical inquiry and sample verification process.