Stainless Steel Coil Tube (Coiltube) — Cylindrical Condensing Coil for Air-Source Heat Pump Water Heaters
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular component designed specifically for use as a cylindrical condensing coil within air-source heat pump water heater (ASHPWH) systems. This product represents a critical heat exchange element that facilitates the transfer of thermal energy from the refrigerant to the water stored within the insulated tank, thereby enabling efficient and reliable hot water production.
Based on extensive research into cylindrical condensing coil water temperature distribution within air-source heat pump water heaters, the design of this coil tube has been optimized to achieve uniform heat transfer, minimize thermal stratification, and maximize the coefficient of performance (COP) of the overall heating system. The coil geometry, tube diameter, pitch, and material selection are all carefully calibrated to ensure optimal thermodynamic performance across a wide range of operating conditions.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, which provides an exceptional combination of corrosion resistance, mechanical strength, and thermal conductivity. The primary material grades utilized include:
- SUS304 (UNS S30400) — General-purpose austenitic stainless steel offering excellent corrosion resistance in most atmospheric and aqueous environments. Contains approximately 18% chromium (Cr) and 8% nickel (Ni).
- SUS316 (UNS S31600) — Enhanced austenitic grade with 2–3% molybdenum (Mo) addition, providing superior resistance to pitting and crevice corrosion, particularly in chloride-containing water environments.
- SUS304L / SUS316L (Low Carbon Grades) — Low-carbon variants designed to resist intergranular corrosion during welding operations, ensuring long-term structural integrity at welded joints.
Key Material Properties
- Corrosion Resistance: Superior resistance to general corrosion, pitting corrosion, and stress corrosion cracking (SCC) in domestic hot water environments.
- Thermal Conductivity: Approximately 16–18 W/(m·K) at 20°C, providing adequate heat transfer performance while maintaining long service life.
- Mechanical Strength: Yield strength of ≥205 MPa (SUS304) and ≥170 MPa (SUS316), ensuring dimensional stability under thermal cycling and pressure loading.
- Temperature Range: Suitable for continuous operation from −196°C to +870°C, with practical operating limits in ASHPWH applications typically between 0°C and 95°C.
- Hygienic Performance: Non-toxic, non-reactive, and compliant with potable water contact standards.
Specifications
| Parameter | Specification / Value |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Material Grade | SUS304 / SUS316 / SUS304L / SUS316L |
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.7 mm (1/2"), 15.88 mm (5/8") — customizable |
| Wall Thickness | 0.5 mm – 1.5 mm (customizable based on application requirements) |
| Coil Inner Diameter (ID) | 100 mm – 500 mm (tailored to tank geometry) |
| Coil Length | Up to 100 m per continuous coil (seamless or welded) |
| Pitch (Center-to-Center Spacing) | 15 mm – 40 mm (optimized for heat transfer efficiency) |
| Number of Turns | Customizable based on required heat exchange area |
| Surface Finish | 2B (cold-rolled and annealed), BA (Bright Annealed), or custom polishing |
| Operating Pressure | Up to 1.6 MPa (232 psi) standard; higher pressures available on request |
| Operating Temperature Range | −40°C to +200°C (ASHPWH typical range: 5°C to 95°C) |
| End Connection Type | Threaded, flanged, brazed, or welded (customizable) |
| Applicable Refrigerants | R134a, R404A, R410A, R290 (propane), R1234ze — HFC/HFO compatible |
| Manufacturing Standard | GB/T 12771, ASTM A213/A269, EN 10217, JIS G3446 |
| Production Capacity | High-volume continuous production with flexible customization |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, mechanical integrity, and surface quality:
- Raw Material Selection and Inspection: High-purity stainless steel strip (coil) is procured from certified suppliers. Incoming material undergoes spectroscopic analysis to verify chemical composition and mechanical property certification.
- Coil Winding / Forming: The stainless steel tube is wound into the specified cylindrical geometry using precision CNC-controlled coil winding machines. The winding process maintains consistent pitch, turn-to-turn spacing, and concentricity throughout the entire coil length.
- Welding (if applicable): For coils requiring continuous seamless tubes, orbital TIG (Tungsten Inert Gas) welding or automatic resistance welding is employed to create leak-tight joints. Weld quality is verified through visual inspection and, where required, dye penetrant testing (DPT) or ultrasonic testing (UT).
- Heat Treatment: Post-welding annealing may be performed to relieve residual stresses and restore the austenitic microstructure, ensuring uniform corrosion resistance throughout the product.
- Surface Treatment: The coil surface undergoes pickling and passivation to remove any oxide scale or discoloration, forming a protective chromium oxide passive layer that enhances long-term corrosion resistance.
- Pressure Testing: Each coil unit is subjected to hydrostatic or pneumatic pressure testing at 1.5 times the maximum operating pressure to verify leak-tightness and structural integrity.
- Final Inspection and Packaging: Dimensions, surface finish, and mechanical properties are verified against specifications. Conforming products are packaged with protective wrapping to prevent mechanical damage during transport.
Applications
The stainless steel coil tube serves as a critical component in a diverse range of thermal management and heat exchange applications:
- Air-Source Heat Pump Water Heaters (ASHPWH): Primary application as the condensing coil within the insulated storage tank, where refrigerant heat is transferred to domestic hot water.
- Domestic Water Heating Systems: Integration into residential and commercial water heating units requiring durable, hygienic heat exchange surfaces.
- Industrial Process Heating: Use in food and beverage processing, pharmaceutical manufacturing, and chemical plants where stainless steel's hygienic and corrosion-resistant properties are mandated.
- Solar-Assisted Water Heating Systems: Hybrid configurations combining solar thermal energy with heat pump technology for enhanced energy efficiency.
- Refrigeration and HVAC Systems: Condenser and evaporator coils in commercial refrigeration units and air conditioning systems.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring that all products meet or exceed international standards:
- ISO 9001:2015 — Quality Management Systems certification, demonstrating a commitment to consistent quality and continuous improvement.
- ISO 14001:2015 — Environmental Management Systems certification, reflecting responsible environmental practices throughout the manufacturing lifecycle.
- CE Marking — Conformity with European Union directives for products intended for the European market.
- GB/T Standards (Chinese National Standards): Compliance with GB/T 12771 (seamless stainless steel tubes for heat exchangers), GB/T 4237 (cold-rolled stainless steel plates and sheets), and related specifications.
- ASTM Standards: Material and product compliance with ASTM A213 (welded and seamless austenitic stainless steel tubes for heat exchangers) and ASTM A269 (welded austenitic stainless steel tubing for chemical and similar severe service).
- EN Standards: Conformity with EN 10217 (seamless stainless steel tubes for heat exchangers and similar applications).
- NSF/ANSI 61: Compliance with drinking water system components standards where applicable.
Unique Selling Points
1. Optimized Thermal Performance Through Research-Driven Design
Unlike conventional coil designs, this product incorporates findings from rigorous academic research on cylindrical condensing coil water temperature distribution within air-source heat pump water heaters. The coil geometry, pitch, and tube arrangement have been specifically engineered to minimize thermal stratification within the storage tank, ensuring more uniform water temperature distribution and higher overall system COP.
2. Superior Corrosion and Fatigue Resistance
The use of high-purity austenitic stainless steel (SUS304/SUS316) provides exceptional resistance to both general corrosion and chloride-induced pitting corrosion. This translates to a significantly extended service life — typically exceeding 15–20 years — compared to copper or aluminum coil alternatives, particularly in hard-water or coastal environments.
3. Hygienic and Food-Safe Construction
The stainless steel surface is inherently non-toxic, non-reactive, and resistant to biofilm formation. This makes the product suitable for applications involving potable water, food processing, and pharmaceutical manufacturing without the need for additional internal coatings or linings.
4. Full Customization and Engineering Flexibility
Wenzhou Jixing Metal Materials Co., Ltd offers comprehensive customization capabilities, including tailored coil diameter, pitch, tube dimensions, material grade selection, and end-connection configurations. This allows OEM (Original Equipment Manufacturer) partners to integrate the coil tube seamlessly into their proprietary system designs.
5. Environmentally Responsible Manufacturing
Stainless steel is 100% recyclable without degradation of material properties. The manufacturing process adheres to ISO 14001 environmental management standards, minimizing waste generation, energy consumption, and carbon footprint throughout the production lifecycle.
6. Competitive Total Cost of Ownership
While the initial material cost may be higher than copper alternatives, the exceptional durability, resistance to corrosion, and minimal maintenance requirements of stainless steel coil tubes result in a significantly lower total cost of ownership (TCO) over the product's service life. The elimination of failure-related downtime and replacement costs further enhances the economic advantage.
Technical Note: The performance of the cylindrical condensing coil within an air-source heat pump water heater is directly influenced by the coil's geometric parameters and the resulting water temperature distribution pattern. Research has demonstrated that optimized coil configurations can improve the volumetric heat transfer coefficient by 15–30% compared to standard designs, directly translating to reduced compressor energy consumption and enhanced user comfort through more consistent hot water delivery.
Technical Support and After-Sales Service
Wenzhou Jixing Metal Materials Co., Ltd provides comprehensive technical support including:
- Custom engineering consultation for coil design optimization
- Material certification and mill test reports (MTR) for every batch
- On-site installation guidance and commissioning support
- Ongoing technical advisory for system performance optimization
- Warranty coverage with clear terms and responsive service response