Stainless Steel Coil Tube for Seawater-Source Heat Pump Heat Exchangers

Product Code: JX-CT-965 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component specifically designed for integration into coil-type heat exchangers utilized in seawater-source heat pump (SWHP) systems. This product represents a critical thermal transfer element that operates under the demanding conditions of marine environments, where prolonged exposure to chlorinated seawater, temperature cycling, and hydraulic pressure necessitates exceptional corrosion resistance and mechanical durability.

Based on extensive numerical simulation research—including Computational Fluid Dynamics (CFD) and Conjugate Heat Transfer (CHT) analyses—the coil tube geometry has been optimized to maximize heat transfer efficiency while minimizing pressure drop across the heat exchanger bundle. The spiral winding configuration provides a high surface-area-to-volume ratio, enabling compact heat exchanger assemblies with superior thermal performance in space-constrained installations.

2. Material & Properties

The coil tube is fabricated from austenitic stainless steel grades engineered to withstand the aggressive electrochemical environment of seawater. The following material specifications are maintained:

Mechanical Properties (AISI 316L, Annealed Condition)

3. Technical Specifications

Parameter Specification Standard Reference
Tube Outer Diameter (OD) 8 mm / 10 mm / 12 mm / 16 mm ASTM A213 / GB/T 12771
Wall Thickness 0.5 mm – 1.5 mm (tolerance ± 10%) ASTM A269
Coil Winding Diameter 25 mm – 200 mm (configurable) Custom per application
Coil Pitch (Helical Spacing) 5 mm – 25 mm (adjustable) CFD-optimized per design
Coil Length (Unwound) 1 m – 50 m (custom orders available) —
Number of Turns 10 – 500 turns Per heat exchanger design
Maximum Working Pressure 1.6 MPa – 6.3 MPa (depending on wall thickness) EN 10216 / ASME B31.3
Hydrostatic Test Pressure 1.5× Working Pressure ISO 11114
Winding Tolerance ± 0.5 mm (diameter), ± 0.3 mm (pitch) Internal QC standard
End Preparation Plain end, beveled, flanged, or threaded Per customer specification
Heat Transfer Coefficient 2,500 – 6,500 W/(m²·K) (typical, seawater-to-refrigerant) CFD simulation validated
Pressure Drop (ΔP) ≤ 50 kPa at design flow rate Optimized via numerical simulation
Surface Roughness (Ra) ≤ 0.4 μm (electropolished); ≤ 0.8 μm (2B finish) ASTM A490

4. Manufacturing Process

The production of the Stainless Steel Coil Tube follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and corrosion resistance:

  1. Raw Material Selection & Inspection: Austenitic stainless steel wire or seamless tube stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition, along with hardness testing and visual inspection per ASTM E10 and ASTM E165.
  2. Cold Drawing / Cold Forming: The tube stock is cold-drawn through calibrated tungsten carbide dies to achieve precise outer diameter and wall thickness. This process work-hardens the material, improving mechanical strength while maintaining ductility for subsequent coiling.
  3. Intermediate Annealing: Where required, the drawn tube is solution-annealed at 1,050–1,100 °C followed by rapid air cooling to restore full austenitic microstructure and relieve accumulated residual stresses.
  4. Precision Spiral Coiling: The tube is wound onto a CNC-controlled helical coiling machine using a mandrel and forming rollers. The winding parameters (diameter, pitch, number of turns) are programmed based on CFD-optimized heat exchanger design data. Real-time tension control ensures uniform spring-back compensation and consistent coil geometry.
  5. Stress Relief Annealing: Post-coiling annealing at 350–450 °C eliminates residual stresses introduced during the forming process, stabilizing the coil geometry and preventing dimensional drift during service.
  6. Pickling & Passivation: The coil tube is immersed in a mixed acid solution (HNO₃/HF) to remove oxide scale, followed by passivation treatment to establish a uniform chromium-rich passive film. This step is critical for seawater service applications.
  7. Electropolishing (Optional): For high-performance applications requiring minimized biofouling and enhanced corrosion resistance, the tube interior and exterior surfaces are electropolished to achieve Ra ≤ 0.4 μm. This process removes the contaminated surface layer and increases the Cr:Fe ratio at the surface.
  8. Non-Destructive Testing (NDT): Each coil tube undergoes 100% eddy current testing (ECT) per ASTM E3092 to detect wall thickness variations, surface defects, and subsurface discontinuities. Additional ultrasonic testing (UT) may be applied per customer requirements.
  9. Hydrostatic Pressure Testing: All coils are pressure-tested at 1.5× the maximum working pressure with a hold time of minimum 10 seconds. Zero leakage is the acceptance criterion.
  10. Final Inspection & Packaging: Dimensional verification using calipers, micrometers, and coordinate measuring machines (CMM). Protective end caps and moisture-absorbent packaging materials are applied before shipment.

5. Applications

The Stainless Steel Coil Tube is engineered for a wide range of thermal management applications, with particular emphasis on the following domains:

5.1 Seawater-Source Heat Pump Systems

Primary application domain. The coil tube serves as the heat transfer element in seawater-to-refrigerant heat exchangers. Numerical simulation studies have demonstrated that the helical coil geometry achieves a Nusselt number (Nu) enhancement of 30–60% compared to straight-tube configurations under turbulent flow conditions (Reynolds number Re > 10,000). The compact coil design reduces the overall heat exchanger footprint while maintaining high thermal efficiency (Carnot efficiency utilization > 85%).

5.2 Marine Cooling & Condenser Systems

Used in shipboard HVAC systems, marine engine cooling loops, and offshore platform thermal management systems where space is at a premium and corrosion resistance is paramount.

5.3 Industrial Process Heating & Cooling

Integration into shell-and-coil heat exchangers for chemical processing, food and beverage pasteurization, pharmaceutical sterilization, and power plant condensate recovery systems.

5.4 Geothermal & Ground-Source Heat Exchangers

Deployment in closed-loop geothermal well systems where the coil tube is installed in boreholes for ground-source heat exchange, leveraging the high thermal conductivity and corrosion resistance of austenitic stainless steel.

5.5 Solar Thermal Collector Systems

Application in evacuated tube solar collectors and flat-plate solar thermal systems where the coil tube interfaces with heat transfer fluids (HTF) under high-temperature cycling conditions.

6. Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring full traceability and compliance with international standards:

7. Unique Selling Points

8. Ordering Information

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.

Product Code: JX-CT-965

Minimum Order Quantity (MOQ): 500 meters (standard specifications); negotiable for custom configurations

Lead Time: 15–30 calendar days for standard orders; 45–60 days for custom-engineered coils

Warranty: 5-year performance guarantee against corrosion-related failure under specified operating conditions