Stainless Steel Coil Tube (Coiltube) — HVAC & Thermal Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product designed for demanding thermal management applications, particularly within heating, ventilation, and air conditioning (HVAC) systems. This product is specifically engineered for integration into fan coil unit (FCU) assemblies, cooling tower supply loops, and office building chilled water distribution networks. The coil tube provides efficient heat transfer through its compact helical geometry, maximizing surface-area-to-volume ratio while maintaining structural integrity under cyclic thermal loading conditions.
As a critical component in the thermal circuit of commercial and industrial HVAC installations, the coil tube facilitates the transfer of thermal energy between working fluids (water, glycol solutions, or refrigerants) and the surrounding medium. The product is manufactured to meet stringent dimensional tolerances and metallurgical specifications, ensuring reliable long-term performance in continuous-duty applications.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, mechanical strength, and weldability. The primary material grades available include:
- AISI 304 / SUS 304 / 1.4301 — General-purpose austenitic stainless steel with excellent corrosion resistance and formability. Suitable for standard HVAC and potable water applications.
- AISI 316L / SUS 316L / 1.4404 — Low-carbon austenitic grade with added molybdenum (Mo) content for superior resistance to chlorides, pitting, and crevice corrosion. Ideal for cooling tower circuits and coastal environments.
- AISI 321 / SUS 321 / 1.4541 — Titanium-stabilized grade offering enhanced resistance to intergranular corrosion at elevated temperatures.
Key Material Properties (AISI 316L Reference):
- Chemical Composition: C ≤ 0.03%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, Mn ≤ 2.0%, Si ≤ 1.0%
- Thermal Conductivity: 16.3 W/(m·K) at 25°C
- Specific Heat Capacity: 500 J/(kg·K)
- Density: 8,000 kg/m³
- Tensile Strength: ≥ 515 MPa (as-supplied, cold-worked condition)
- Yield Strength: ≥ 205 MPa (0.2% offset)
- Operating Temperature Range: −196°C to +400°C
- Surface Finish: 2B, BA (Bright Annealed), or custom polished (Ra ≤ 0.4 μm)
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Product Category | HVAC Thermal Exchange Components |
| Material Grades | AISI 304, 316L, 321, 304L, 316 |
| Tube Outer Diameter (OD) | 6.0 mm – 25.4 mm (1/4" – 1") |
| Tube Wall Thickness | 0.5 mm – 1.5 mm |
| Coil Diameter | 200 mm – 1,500 mm (configurable) |
| Coil Pitch (Turn Spacing) | 8 mm – 25 mm (customizable per design) |
| Coil Length | 5 m – 100 m per coil (standard) |
| Dimensional Tolerance (OD) | ±0.05 mm (precision cold-drawn) |
| Dimensional Tolerance (Wall) | ±0.02 mm |
| End Condition | Plain end, threaded, flanged, or crimped (per request) |
| Surface Treatment | Passivated, pickled, or custom finish |
| Maximum Operating Pressure | ≤ 2.5 MPa (depending on OD and wall thickness) |
| Maximum Operating Temperature | ≤ 200°C (standard); ≤ 400°C (grade-dependent) |
| Applicable Standards | ASTM A213, ASTM A269, ASME B36.19M, EN 10216-5, GB/T 12771 |
| Order Quantity (MOQ) | Negotiable based on specification |
| Customization | Available — diameter, pitch, length, end treatment, and material grade |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorously controlled multi-stage process to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Raw Material Selection: Virgin stainless steel wire rod or seamless tube stock is procured from certified mills. Incoming material undergoes spectroscopic verification (PMI — Positive Material Identification) to confirm chemical composition compliance with ASTM/EN specifications.
- Cold Drawing: Seamless tube stock is cold-drawn through precision tungsten carbide dies to achieve the target outer diameter and wall thickness within tight tolerances. This process enhances mechanical properties through strain hardening and produces a smooth internal and external surface finish.
- Intermediate Annealing: At specified reduction stages, the tube is annealed in a controlled atmosphere (protective gas or vacuum) to relieve cold-work stresses, restore ductility, and prevent work hardening-induced cracking. Annealing temperatures are maintained between 1,050°C and 1,150°C with rapid cooling to prevent grain coarsening.
- Coiling / Helical Forming: The straight tube is helically formed around precision mandrels using CNC-controlled coiling machines. The forming process is performed at ambient temperature to preserve the cold-worked mechanical properties. Coil diameter, pitch, and turn count are controlled to ±0.5 mm accuracy.
- Welding (if applicable): For continuous coil tube configurations, butt welds or orbital TIG welds are applied at tube joints. Weld quality is verified through visual inspection and, where required, radiographic testing (RT) or dye penetrant testing (PT).
- Pickling and Passivation: The formed coil tube is subjected to acid pickling (nitric/hydrofluoric acid mixture) to remove oxide scale and contaminants. A subsequent passivation treatment (nitric acid or citric acid) forms a protective chromium oxide film, enhancing long-term corrosion resistance.
- Final Inspection and Testing: Each coil tube undergoes dimensional verification (OD, wall thickness, coil diameter, pitch), surface quality assessment, pressure testing (hydrostatic or pneumatic), and chemical composition verification. Non-destructive testing (NDT) is performed as specified.
Applications
The stainless steel coil tube is deployed across a wide range of thermal and fluid transport applications, with particular emphasis on the following domains:
- Fan Coil Units (FCU): The coil tube serves as the primary heat exchange element in fan coil units installed in commercial office buildings, hotels, hospitals, and institutional facilities. The helical coil configuration optimizes heat transfer between the chilled or heated water circuit and the forced-air stream, enabling precise indoor temperature control.
- Cooling Tower Supply Circuits: In office building HVAC systems employing cooling tower configurations, the coil tube is utilized in the condenser and evaporator loops, where it withstands continuous exposure to water with variable mineral content, dissolved oxygen, and biological contaminants.
- Chilled Water Distribution: The coil tube is integrated into secondary chilled water loops, providing efficient thermal distribution to terminal units across multi-story commercial buildings.
- Industrial Heat Exchangers: Compact coil tube assemblies are employed in shell-and-tube heat exchangers, plate-and-frame heat exchangers, and air-to-fluid heat exchangers in manufacturing processes requiring precise temperature regulation.
- Refrigeration and Air Conditioning Systems: The coil tube functions as a refrigerant-side or water-side component in vapor-compression refrigeration cycles, where its corrosion resistance ensures long service life in the presence of ammonia, HFC, or HFO refrigerants.
- Domestic Hot Water and Sanitary Systems: In residential and commercial plumbing applications, the coil tube is used in underfloor heating systems, radiant floor heating circuits, and domestic hot water recirculation loops.
- Food Processing and Pharmaceutical Equipment: The hygienic surface finish and corrosion resistance of AISI 316L coil tubes make them suitable for sanitary heat exchangers in food, beverage, and pharmaceutical manufacturing.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all coil tube products meet international standards and regulatory requirements:
- ISO 9001:2015 — Quality Management System certification demonstrating adherence to internationally recognized quality management principles.
- ISO 14001:2015 — Environmental Management System certification ensuring environmentally responsible manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- CE Marking — Conformity with European Union directives for pressure equipment and construction products.
- Material Traceability: Each production batch is accompanied by a Material Test Certificate (MTC / EN 10204 3.1) documenting chemical composition, mechanical properties, and heat treatment history.
- Pressure Vessel Testing: Hydrostatic pressure testing performed in accordance with ASME Section VIII / EN 13445 requirements, with test pressure typically set at 1.5× the maximum design pressure.
- Non-Destructive Testing (NDT): Available upon request — including radiographic testing (RT), ultrasonic testing (UT), and magnetic particle inspection (MT) for weld and tube body integrity verification.
- Applicable Standards Compliance: ASTM A213 (seamless austenitic stainless steel tube), ASTM A269 (wrought austenitic stainless steel tube), ASME B36.19M (welded and seamless wrought stainless steel pipe), EN 10216-5 (welded hollow sections of stainless steel), GB/T 12771 (Chinese national standard for welded stainless steel tubes).
Unique Selling Points
- Superior Corrosion Resistance: The austenitic stainless steel matrix, particularly in AISI 316L grade with molybdenum alloying, provides exceptional resistance to pitting, crevice corrosion, and general attack in cooling tower water, glycol solutions, and industrial process fluids — significantly extending service life compared to carbon steel alternatives.
- Optimized Thermal Performance: The precision-coiled helical geometry maximizes the heat transfer surface area per unit volume, enabling compact and efficient heat exchanger designs ideal for space-constrained commercial HVAC installations.
- Dimensional Precision: CNC-controlled coiling processes ensure coil diameter, pitch, and tube geometry accuracy within ±0.5 mm, facilitating seamless integration into pre-engineered fan coil unit and heat exchanger assemblies.
- Hygienic Surface Quality: Available in Bright Annealed (BA) and polished finishes with surface roughness as low as Ra ≤ 0.4 μm, meeting sanitary requirements for food, pharmaceutical, and medical applications.
- Customization Capability: Flexible manufacturing infrastructure supports bespoke coil diameters, pitches, tube lengths, end treatments, and material grades to accommodate specific project requirements and engineering designs.
- Full Traceability and Documentation: Comprehensive quality documentation, including MTCs, NDT reports, and dimensional inspection records, ensures full supply chain traceability and regulatory compliance for critical infrastructure projects.
- Environmental Sustainability: The use of recyclable stainless steel materials and adherence to ISO 14001 environmental management standards aligns with global sustainability objectives and green building certification requirements (LEED, BREEAM).
Design Considerations for Cooling Tower Supply Applications
In the context of office building HVAC systems utilizing cooling tower supply configurations with fan coil units, the selection and design of coil tube components must account for several critical engineering parameters:
The cooling tower supply water temperature directly influences the thermal load on fan coil unit coils. Typical cooling tower supply temperatures range from 28°C to 32°C, with the coil tube operating within a secondary chilled water circuit at 6°C to 12°C supply and 16°C to 22°C return. The stainless steel coil tube must therefore withstand thermal cycling between ambient conditions and refrigerated water temperatures while resisting scaling and biofilm formation in the cooling tower water loop.
- Thermal Cycling Fatigue: The coil tube is designed to withstand repeated thermal expansion and contraction cycles without degradation of mechanical properties or joint integrity.
- Scaling Resistance: The smooth internal surface finish of cold-drawn stainless steel tube minimizes mineral scale deposition, maintaining consistent flow characteristics and heat transfer coefficients over the service life.
- Legionella Mitigation: The corrosion-resistant surface and smooth bore geometry reduce biofilm adhesion, supporting water quality management protocols required to mitigate Legionella pneumophila risk in cooling tower systems.
- Flow Resistance Optimization: The coil pitch and tube diameter are selected to balance heat transfer efficiency against acceptable pressure drop, ensuring that the circulating pump operates within its design envelope.