Stainless Steel Coil Tube — Ground Source Heat Pump Heat Exchanger Coil

Product Overview

The Stainless Steel Coil Tube (Coil Tube) is a precision-engineered tubular heat exchanger component manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into Ground Source Heat Pump (GSHP) Air Conditioning Systems. This product represents a critical component in the thermal exchange subsystem, where the coil tube facilitates efficient heat transfer between the circulating refrigerant or water medium and the surrounding ground loop or building heating/cooling infrastructure.

Based on extensive simulation and experimental validation of ground source heat pump systems, the coil tube geometry, material selection, and dimensional tolerances have been optimized to maximize heat exchange efficiency (HX Efficiency) while minimizing pressure drop (ΔP) across the coil. The product is engineered to withstand the cyclic thermal loading, mechanical stress, and long-term corrosion exposure inherent in geothermal energy applications.

Material & Properties

The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior combination of corrosion resistance, thermal conductivity, mechanical strength, and long-term durability in geothermal environments.

• Base Alloy: Austenitic stainless steel conforming to ASTM A213 / GB/T 14976 standards, with primary grades including 304 (06Cr19Ni10), 316 (06Cr17Ni12Mo2), and 321 (06Cr18Ni11Ti).
• Corrosion Resistance: Exceptional resistance to chloride-induced pitting (Pitting Resistance Equivalent Number, PREN ≥ 19 for 316 grade), intergranular corrosion, and stress corrosion cracking (SCC) in geothermal brine and soil-contact environments.
• Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, providing adequate heat transfer performance while maintaining structural integrity under thermal cycling.
• Mechanical Properties: Tensile strength (UTS) ≥ 520 MPa; Yield strength (YS) ≥ 205 MPa; Elongation (A₅₀) ≥ 40%; ensuring resistance to ground settlement loads and thermal expansion stresses.
• Operating Temperature Range: −196°C to +870°C, accommodating the full thermal envelope of GSHP systems including defrost cycles and peak heating/cooling loads.
• Surface Finish: Electropolished or passivated inner surface (Ra ≤ 0.4 μm) to minimize fouling, reduce fluid friction losses, and enhance heat transfer coefficients.

Specifications

Parameter	Specification	Standard / Reference
Product Name	Stainless Steel Coil Tube (Coil Tube)	Internal designation: No. 1135
Manufacturer	Wenzhou Jixing Metal Materials Co., Ltd	—
Material Grade	SUS 304 / 316 / 321 (Austenitic SS)	ASTM A213 TP304/316/321; GB/T 14976
Outer Diameter (OD)	Φ 9.52 mm, Φ 12.7 mm, Φ 15.88 mm, Φ 19.05 mm (customizable)	ASTM A213; EN 10216-5
Wall Thickness	1.00 mm – 3.00 mm (typical: 1.24 mm / 1.65 mm)	ASTM A213 tolerances
Coil Pitch (Helical Spacing)	15 mm – 50 mm (optimized per system design)	Simulation-validated per GSHP thermal model
Coil Diameter (Bundle OD)	Φ 200 mm – Φ 1200 mm (customizable)	Per engineering design specification
Coil Length / Turns	Up to 50 m continuous coil; multi-turn configurations	—
End Preparation	Deburred, beveled, or threaded (per customer requirement)	ASME B1.20.1 (threaded); ISO 228
Dimensional Tolerance	OD: ±0.05 mm; Wall thickness: ±0.05 mm	ASTM A213; GB/T 14976
Maximum Working Pressure	2.5 MPa (standard); up to 6.3 MPa (reinforced)	ASME BPV Code Section VIII
Hydrostatic Test Pressure	1.5× Working Pressure (minimum 3.75 MPa)	ASME BPV Code; EN 12452
Surface Treatment	Electropolished / Passivated / Shot-blasted (inner/outer)	ASTM A967; ASTM B571
Heat Transfer Coefficient (U)	≥ 800 W/(m²·K) (optimized coil geometry)	Simulation-validated per GSHP model
Pressure Drop (ΔP)	≤ 15 kPa per meter (at design flow rate)	Hydraulic simulation validated
Design Service Life	≥ 25 years (geothermal application)	Based on corrosion rate analysis & field data

Manufacturing Process

The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and performance reliability:

1. Raw Material Selection & Inspection:

   Virgin stainless steel seamless tubes are sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) for chemical composition verification, ultrasonic testing (UT) for internal defect detection, and visual inspection for surface quality.

2. Tube Straightening & Calibration:

   Seamless tubes are straightened and calibrated to precise OD and wall thickness tolerances using hydraulic expansion or cold-drawing equipment, ensuring uniform cross-sectional geometry prior to coiling.

3. Coiling / Spiral Forming:

   Tubes are wound into helical coils using CNC-controlled coiling machines. The coil pitch, diameter, and turn count are programmed per the engineering design specification. Real-time monitoring ensures consistent helical geometry and minimizes plastic deformation during forming.

4. Welding & Joining:

   Where continuous coil length requires splicing, high-purity argon-shielded TIG welding (GTAW) is employed in accordance with ASME Section IX. Weld joints are ground flush and subjected to 100% visual and dye penetrant inspection (DPI).

5. Stress Relief Annealing:

   Coils undergo controlled heat treatment (1050°C–1150°C for 304/316 grades) in inert atmosphere to relieve residual stresses from forming, restore full austenitic microstructure, and maximize corrosion resistance and ductility.

6. Surface Finishing:

   Electropolishing or chemical passivation is applied to the inner and outer surfaces to remove scale, oxides, and residual contaminants. This step is critical for geothermal applications where fluid cleanliness directly impacts heat transfer efficiency and long-term fouling resistance.

7. Hydrostatic & Non-Destructive Testing:

   Each coil undergoes 100% hydrostatic pressure testing at 1.5× the maximum working pressure, held for a minimum dwell time per ASME BPV Code. Additional UT and eddy current testing (ECT) are performed on weld joints and critical sections.

8. Final Dimensional Inspection & Packaging:

   Finished coils are measured for OD, wall thickness, coil pitch, and total length using precision calipers, ultrasonic thickness gauges, and laser profilometry. Products are packaged with desiccant protection and clearly marked with material certificates, traceability numbers, and test reports.

Applications

The stainless steel coil tube is engineered for demanding thermal exchange applications, with primary deployment in the following sectors:

• Ground Source Heat Pump (GSHP) Systems:

  Primary application domain. The coil tube serves as the heat exchanger element in vertical and horizontal ground loop configurations, transferring thermal energy between the circulating fluid (water/antifreeze) and the subsurface geothermal reservoir. Simulation-validated coil geometry ensures optimal heat capture during winter heating cycles and heat rejection during summer cooling cycles.

• Geothermal Water-to-Water Heat Exchangers:

  Shell-and-coil heat exchanger configurations where the stainless steel coil tube is mounted within a pressure vessel, exchanging heat between geothermal brine and district heating/cooling water loops.

• Industrial Process Heating & Cooling:

  Application in chemical processing, food and beverage production, and pharmaceutical manufacturing where corrosion-resistant heat exchange is required for process fluid temperature control.

• Marine & Offshore Heat Exchangers:

  Utilization in shipboard HVAC systems and offshore platform thermal management, leveraging the superior chloride corrosion resistance of 316/316L grade stainless steel.

• Refrigeration & Air Conditioning Systems:

  Evaporator and condenser coils in commercial and industrial refrigeration units, where the coil tube provides high-efficiency phase-change heat transfer under cyclic thermal loading.

• Renewable Energy Systems:

  Integration into solar thermal collectors, air-source heat pump units, and hybrid energy systems requiring durable, high-performance tubular heat exchange components.

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring that every coil tube product meets international standards and regulatory requirements:

• ISO 9001:2015 — Quality Management System certification ensuring consistent process control and continuous improvement.
• ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
• ASME BPV Code Section VIII — Compliance for pressure-containing components, including hydrostatic testing and material traceability.
• EN 10216-5 — European standard for stainless steel tubes for heat exchangers and general heat transfer applications.
• ASTM A213 — American standard for seamless austenitic stainless steel tubes for heat exchangers and similar high-temperature service.
• GB/T 14976 — Chinese national standard for seamless stainless steel tubes for heat exchangers and general heat transfer.
• CE Marking — Conformity with European Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU).
• TÜV Certification — Independent third-party inspection and certification of manufacturing processes and product quality.
• Mill Test Certificates (MTC) — EN 10204 Type 3.1 certificates provided with each shipment, documenting chemical composition, mechanical properties, and test results.

Unique Selling Points: The coil tube product line from Wenzhou Jixing Metal Materials Co., Ltd is distinguished by its simulation-validated thermal design, derived from rigorous computational fluid dynamics (CFD) and thermal modeling of ground source heat pump systems. This ensures that each coil geometry is optimized for maximum heat transfer efficiency (U-value) and minimum hydraulic resistance (ΔP) at the system level — not merely at the component level. Combined with strict adherence to international material and fabrication standards, full traceability from raw material to finished product, and a proven track record in geothermal energy applications, this product offers a reliable, high-performance solution for next-generation sustainable HVAC and thermal management systems.