Stainless Steel Helical Coil Tube — Surface Water Source Heat Pump Grade
Product Overview
The Stainless Steel Helical Coil Tube is a precision-engineered continuous tube formed into a helical (spiral) geometry, designed primarily for use in surface water source heat pump systems and geothermal thermal exchange applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube product combines the superior corrosion resistance of austenitic stainless steel with an optimized helical geometry to maximize heat transfer efficiency in submerged or buried thermal exchange configurations.
The helical coil configuration provides a significant increase in effective heat exchange surface area per unit of installation volume compared to straight pipe installations. This geometric advantage is particularly critical in underwater and subsurface heat pump applications where space constraints and environmental conditions demand high-performance thermal performance within compact footprints.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel grades, selected for their exceptional resistance to chloride-induced pitting and crevice corrosion in aqueous environments. The primary material grades employed include:
- 304 (UNS S30400 / 1.4301): General-purpose austenitic grade with excellent formability and corrosion resistance in most non-aggressive water environments. Composition: ≥18% Cr, ≥8% Ni, ≤0.08% C.
- 316 (UNS S31600 / 1.4401): Molybdenum-enhanced grade offering superior resistance to chloride pitting and stress corrosion cracking (SCC). Composition: ≥16.5% Cr, ≥10% Ni, ≥2% Mo, ≤0.08% C.
- 316L (UNS S31603 / 1.4404): Low-carbon variant of 316 with enhanced weldability and resistance to sensitization. Carbon content ≤0.03%.
Key Mechanical Properties (316L Grade):
- Tensile Strength: ≥515 MPa (74,700 psi)
- Yield Strength (0.2% Offset): ≥205 MPa (29,700 psi)
- Elongation: ≥40%
- Thermal Conductivity: 14.9 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
- Operating Temperature Range: −196°C to +870°C
Specifications
| Parameter | Specification / Range |
|---|---|
| Product Category | Helical Coil Tube (盘管 / Coil Tube) |
| Outer Diameter (OD) | 12 mm – 60 mm (configurable per project requirements) |
| Wall Thickness | 0.5 mm – 2.0 mm |
| Coil Pitch (Helical Spacing) | 15 mm – 80 mm (adjustable for flow/heat transfer optimization) |
| Coil Diameter | 100 mm – 600 mm |
| Tube Length (Per Coil) | Up to 120 m continuous coil |
| Material Grade | SUS 304 / 304L / 316 / 316L (default: 316L) |
| Surface Finish | Mill Finish (2B), Polished (No. 4), or Electropolished (Ra ≤ 0.4 μm) |
| End Forming | Plain, Threaded (G/BSP/NPT), Flanged, or Beveled for welding |
| Pressure Rating | Up to 1.6 MPa (standard); 4.0 MPa (reinforced wall thickness) |
| Applicable Standards | ASTM A213/A213M, GB/T 12771, EN 10216-5, JIS G3459 |
| Maximum Operating Temperature | +350°C (continuous); +870°C (intermittent) |
| Minimum Operating Temperature | −196°C (cryogenic capable, no ductile-to-brittle transition) |
| Corrosion Resistance | Pitting Resistance Equivalent Number (PREN): ≥24 (316L) |
| Coil Mass (Typical) | 50 kg – 300 kg per coil assembly |
Manufacturing Process
The production of stainless steel helical coil tubes follows a rigorously controlled multi-stage process to ensure dimensional accuracy, mechanical integrity, and corrosion performance:
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tube blanks conforming to ASTM A213 or GB/T 12771 specifications. Incoming materials undergo spectrographic analysis (OES) to verify chemical composition within specified limits.
- Coil Forming (Helical Bending): The straight tube is passed through precision helical forming dies using a progressive bending machine. The forming process maintains a controlled bending radius (typically ≥ 3× tube OD) to prevent wall thinning, ovality deformation, or internal buckling. Forming speed and die geometry are optimized to achieve uniform pitch and coil diameter tolerances.
- Post-Forming Heat Treatment: Where applicable, the formed coil undergoes solution annealing at 1050–1100°C followed by rapid quenching to restore full austenitic microstructure, eliminate cold-work hardening, and maximize corrosion resistance. For 316L grade, this step ensures carbide precipitation is avoided.
- Dimensional Inspection: Each coil is measured for outer diameter, wall thickness, coil diameter, pitch uniformity, and total length using coordinate measuring machines (CMM) and ultrasonic thickness gauges. Acceptance tolerances conform to EN 10216-5 dimensional requirements.
- Surface Cleaning & Passivation: Coils are cleaned using approved solvents to remove oils, scale, and handling contaminants. Chemical passivation (nitric acid or citric acid treatment) is performed to establish a protective chromium oxide passive film on the surface, ensuring long-term corrosion resistance.
- Hydrostatic Pressure Testing: Each coil undergoes hydrostatic testing at 1.5× the maximum design pressure for a minimum dwell time of 60 seconds to verify leak-free integrity and structural soundness.
- End Finishing & Packaging: Coil ends are machined, threaded, or flanged per customer specifications. Finished coils are wrapped in moisture-barrier protective film and strapped for secure transport.
Applications
The stainless steel helical coil tube is engineered for demanding thermal exchange applications, with particular emphasis on the following domains:
- Surface Water Source Heat Pumps: Submerged helical coil configurations serve as the primary heat exchanger in surface water (lake, river, reservoir) heat pump systems. The helical geometry increases turbulence and heat transfer coefficient compared to straight pipe, improving Coefficient of Performance (COP) by 15–25%. The stainless steel construction resists biofouling, scaling, and corrosion in variable-quality surface waters.
- Ground Source Heat Pumps (GSHP): Buried helical coils in boreholes or horizontal trenches provide efficient geothermal heat extraction or rejection with minimal land footprint.
- Industrial Process Cooling/Heating: Used in chemical processing, food and beverage pasteurization, pharmaceutical manufacturing, and semiconductor cooling loops where non-contaminating, corrosion-resistant tubing is mandatory.
- Marine and Offshore Systems: Seawater heat exchangers, ballast water treatment systems, and subsea thermal management where chloride resistance is critical.
- Central Heating and District Energy: Coil-based heat exchangers in district heating networks and building energy systems.
- Cryogenic Applications: Liquefied natural gas (LNG) heat exchangers and cryogenic fluid transfer systems where the austenitic stainless steel retains full ductility at temperatures below −196°C.
Unique Selling Points
- Superior Helical Geometry Optimization: Proprietary coil forming technology achieves pitch uniformity within ±0.5 mm across the entire coil length, ensuring consistent fluid dynamics and heat transfer performance. This level of precision is validated through performance testing consistent with methodologies described in published research on underwater helical coil heat exchangers.
- Enhanced Corrosion Durability: Default 316L material selection with PREN ≥ 24 provides exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-rich environments (surface water, seawater, brackish water). Expected service life exceeds 25 years in typical aqueous heat pump applications.
- Thermal Performance Advantage: The helical configuration induces secondary Dean vortices within the tube, significantly enhancing turbulent heat transfer. Measured heat transfer coefficients are 30–50% higher than equivalent straight-tube installations, reducing required coil length and system footprint.
- Full Traceability & Certification: Every coil batch is accompanied by a full material test certificate (MTC) in accordance with EN 10204 3.1, traceable to the steel mill heat number. Comprehensive documentation includes chemical analysis, mechanical test results, and dimensional inspection reports.
- Customizable Configurations: Flexible manufacturing capability allows customization of tube diameter, wall thickness, coil geometry, pitch, end connections, and surface finish to meet specific project engineering requirements.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality management and product certifications:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and quality assurance processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ISO/IEC 17025 — Laboratory accreditation for in-house testing capabilities including chemical analysis, mechanical testing, and dimensional metrology.
- Product Standards Compliance: ASTM A213/A213M (Seamless and Welded Austenitic Stainless Steel Tubing), GB/T 12771 (Stainless Steel Seamless Tubes for General Purposes), EN 10216-5 (Seamless and Welded Stainless Steel Tubes for Pressure Purposes), JIS G3459.
- Material Certifications: Full EN 10204 Type 3.1 material test certificates for each production batch, including spectrometric chemical analysis, tensile testing, impact testing (where applicable), and hydrostatic test records.
- Non-Destructive Testing (NDT): Available upon request — eddy current testing (ECT) for surface and near-surface defect detection; ultrasonic testing (UT) for volumetric flaw detection.
Technical Note: Performance data referenced in this specification, particularly regarding heat transfer enhancement factors and COP improvements for helical coil configurations, are derived from validated experimental methodologies consistent with published research on surface water source heat pump underwater helical coil performance testing (《地表水源热泵的水下螺旋盘管性能测试》). Field performance may vary depending on water quality, flow velocity, temperature differential, and system design parameters. Wenzhou Jixing Metal Materials Co., Ltd. recommends detailed engineering consultation for project-specific applications.