Stainless Steel Coil Tube — Dynamic-Response Optimized Fan Coil Tube
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., the Stainless Steel Coil Tube (Catalog No. 1042) is a precision-engineered coiled piping solution designed for fan coil unit (FCU) heat exchangers and thermofluid transport systems. This product line integrates metallurgical excellence with dynamic-response optimization, ensuring superior thermal-hydraulic performance under variable operational loads and external disturbances.
1. Product Overview
The Coil Tube is a continuously wound, helical stainless steel pipe formed into a compact coil configuration. Unlike straight-tube heat exchangers, coil tubes offer a significantly larger heat transfer surface area per unit volume, making them ideal for compact fan coil units, air handling systems, and industrial heat recovery applications. The dynamic-response characteristics of this coil tube have been rigorously studied under external disturbance conditions — including fluctuating inlet temperatures, variable flow rates, and transient pressure loads — resulting in a product optimized for stable thermal output during dynamic operating scenarios.
Key engineering insights derived from dynamic-response analysis inform the coil geometry, wall thickness distribution, and material selection, ensuring minimal thermal lag and rapid recovery from load perturbations.
2. Material & Properties
2.1 Base Material Composition
- Primary Grade: AISI 304 / ASTM A213 TP304 — the industry-standard austenitic stainless steel offering excellent corrosion resistance and formability.
- Alternative Grades: AISI 316L (enhanced chloride resistance), AISI 321 (stabilized for high-temperature service), and custom duplex grades upon request.
- Carbon Equivalent (CE): < 0.04% (low-carbon variant available for weldability-critical applications).
2.2 Mechanical Properties (Typical, Annealed Condition)
- Tensile Strength (UTS): ≥ 520 MPa (AISI 304)
- Yield Strength (0.2% Proof): ≥ 205 MPa
- Elongation (A50mm): ≥ 40%
- Hardness: ≤ 217 HB (annealed)
2.3 Thermal & Corrosion Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C
- Specific Heat Capacity: 479 J/(kg·K) at 20 °C
- Operating Temperature Range: −196 °C to +870 °C
- Corrosion Resistance: Immune to atmospheric corrosion, resistant to dilute acids, alkalis, and organic solvents; 316L grade offers superior resistance to chlorides and marine environments.
- Crystal Structure: Face-Centered Cubic (FCC) — non-magnetic in annealed condition, ensuring no interference with adjacent magnetic sensors in FCU control systems.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (¼" – 1") | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.4 mm – 2.0 mm | ASTM A269 / EN 10217 |
| Coil Diameter (Center-to-Center) | 150 mm – 600 mm | Custom per application |
| Coil Length (Developed Length) | 1 m – 50 m (continuous) | Custom per application |
| Number of Turns | 5 – 50 turns | Custom per application |
| Surface Finish | 2B (mill finish), BA (bright annealed), or No. 4 brushed | ASTM A480 |
| Surface Roughness (Ra) | ≤ 0.4 μm (BA finish); ≤ 1.6 μm (2B finish) | ISO 1302 |
| Roundness Tolerance | ± 0.5% of OD | ASTM A213 |
| Dimensional Tolerance (OD) | ± 0.1 mm (precision grade); ± 0.2 mm (standard grade) | GB/T 14976 |
| Dimensional Tolerance (Wall) | ± 10% of nominal wall thickness | ASTM A213 |
| Pressure Rating (Hydrostatic Test) | 2.5 × Working Pressure (minimum 1.0 MPa) | ASME B31.9 |
| Maximum Working Pressure | Up to 4.0 MPa (design-dependent) | Calculated per Barlow's formula |
| Dynamic Response Time (Thermal Lag) | ≤ 30 seconds (optimized coil geometry) | Internal test protocol |
| Recovery Time (Post-Disturbance) | ≤ 60 seconds to 95% steady-state output | Internal test protocol |
| Delivery Condition | Annealed (soft), Solution-Treated, or Cold Worked (½-H) | ASTM A213 |
| End Treatment | Plain cut, beveled (15°), or pre-soldered cap | Custom per application |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement & Inspection: Hot-rolled stainless steel strip or seamless tube blanks are sourced from certified mills (e.g., POSCO, Outokumpu, Taiyuan Stainless Steel). Each batch undergoes spectroscopic composition verification (OES), mechanical property testing, and surface inspection prior to processing.
- Blank Preparation: For welded coil tubes, strip is slit to precise width and subjected to edge-trimming and surface cleaning. For seamless coil tubes, bar stock is pierced and drawn to the target OD and wall thickness.
- Coil Forming: A CNC-controlled coil winding machine forms the tube into the specified helical geometry. The forming process is optimized to minimize residual stress and prevent work-hardening-induced loss of ductility. The coil pitch, diameter, and number of turns are controlled within ± 1.5 mm tolerance.
- Stress Relief Annealing: The formed coil is annealed at 1050–1100 °C in a protective atmosphere (hydrogen or nitrogen) to relieve forming stresses, restore full annealed mechanical properties, and enhance corrosion resistance through chromium carbide re-dissolution.
- Pickling & Passivation: The annealed coil is pickled (HNO₃/HF mixed acid) to remove oxide scale, followed by passivation (dilute HNO₃) to form a protective chromium oxide layer (≥ 0.5 μm thickness).
- Surface Finishing: Bright Annealing (BA) is performed in a reducing atmosphere for applications requiring low surface roughness and high aesthetic quality. Electropolishing is available upon request for critical sanitary or chemical applications.
- Quality Inspection: Each coil undergoes hydrostatic pressure testing (per ASME B31.9), dimensional verification (laser micrometer and coordinate measuring machine), surface defect inspection (visual + magnetic particle for ferromagnetic grades), and dynamic-response thermal testing on sampled units.
- Packaging & Shipping: Coils are wrapped in moisture-barrier film, secured on wooden pallets with steel strapping, and labeled with mill test certificates (MTC), heat numbers, and dimensional data.
4.2 Dynamic-Response Optimization
Based on experimental research into the dynamic response of fan coil units under external disturbances (fluctuating air-side temperatures, variable refrigerant flow rates, and step-load changes), the coil geometry parameters — including pitch, turn spacing, and developed length — are optimized to minimize thermal inertia and maximize transient heat transfer efficiency. This results in a coil tube that achieves steady-state thermal output within 30 seconds of a step disturbance and recovers to ≥ 95% of nominal performance within 60 seconds of a sustained perturbation.
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCU): Core heat exchanger element in commercial HVAC systems for office buildings, hospitals, hotels, and retail spaces. The optimized dynamic response ensures rapid temperature stabilization when occupants enter or leave zones.
- Air Handling Units (AHU): Chilled water and hot water coil sections for large-scale ventilation and air conditioning systems.
- Industrial Heat Recovery: Exhaust heat recovery systems in manufacturing facilities, leveraging the corrosion-resistant properties of 316L grade for flue gas environments.
- Food & Beverage Processing: Sanitary-grade heat exchangers for pasteurization, CIP (Clean-In-Place) systems, and process heating/cooling, utilizing BA or electropolished finishes meeting FDA and 3-A Sanitary standards.
- Pharmaceutical & Biotech: GMP-compliant fluid transport and heat exchange in cleanroom environments.
- Marine & Offshore: Seawater cooling coils and ballast water system components, utilizing 316L grade for chloride-induced stress corrosion crack (SCC) resistance.
5.2 Emerging Applications
- Data Center Cooling: Precision cooling loops for server rack-level liquid cooling systems, where rapid thermal response is critical to maintaining IT equipment within thermal limits.
- Renewable Energy Systems: Heat transfer coils in solar thermal collectors and ground-source heat pump loops.
- Automotive Thermal Management: EV battery thermal management loop components.
6. Quality Certifications & Compliance
6.1 Certifications
- ISO 9001:2015 — Quality Management System certification covering the entire production chain from raw material intake to finished product dispatch.
- ISO 14001:2015 — Environmental Management System certification, ensuring sustainable manufacturing practices and waste minimization.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- NADCAP — Special processes accreditation (welding, heat treatment, and surface treatment) for aerospace and defense supply chain eligibility.
- CE Marking — Conformity with European Union directives (PED 2014/68/EU for pressure equipment; Machinery Directive 2006/42/EC for FCU integration).
- UL / CSA — Underwriters Laboratories certification for components used in listed HVAC equipment.
6.2 Material Certifications
- EN 10204 3.1 / 3.2 — Mill Test Certificates (MTC) with full chemical composition and mechanical property data per heat number.
- EN 10204 3.1 — Third-party inspection certificates available upon request.
- Material Traceability: Full heat-number traceability from mill of origin through all processing stages, with digital documentation accessible via the company's ERP system.
6.3 Standards Compliance
| Standard | Scope |
|---|---|
| ASTM A213 / A213M | Seamless stainless steel tubes for high-temperature service |
| ASTM A269 / A269M | Welded austenitic stainless steel tubes for chemical and heat-exchange service |
| EN 10217-7 | Non-ferrous seamless tubes for heat exchange (stainless steel) |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes for fluid transport |
| ASME B31.9 | Pressure Piping — Refrigeration and Air-Conditioning |
| EN 12729 | Stainless steel tubes for heat exchangers |
| 3-A Sanitary Standards | Sanitary design and construction for food, dairy, and pharmaceutical equipment |
7. Unique Selling Points
- Dynamic-Response Optimized Geometry: Coil pitch, turn spacing, and developed length are engineered based on validated transient thermal-hydraulic models, achieving thermal lag ≤ 30 seconds and recovery time ≤ 60 seconds — significantly outperforming standard coil geometries.
- Full Material Traceability: Every coil tube is traceable to its originating mill heat number, with digital documentation of composition, mechanical properties, and processing history at each stage.
- Multi-Grade Flexibility: Availability in 304, 316L, 321, and custom duplex grades allows precise matching of material properties to the service environment, from atmospheric HVAC to aggressive marine and chemical applications.
- Precision Dimensional Control: CNC