Stainless Steel Coil Tube (盘管 / Coiltube) — HVAC & Industrial Applications
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Catalogue Reference: No. 1297
Classification: Literature Study & Technical Reference Series
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for thermal exchange, fluid conveyance, and structural applications in HVAC (Heating, Ventilation, and Air Conditioning) systems, industrial process plants, and building services. The product is supplied in continuous coil form, facilitating downstream forming, cutting, and assembly operations with minimal material waste.
This product line has been extensively studied and validated in conjunction with Two-Pipe Fan Coil Unit (二管制风机盘管) plus Fresh Air (新风) Systems used for air-conditioned inner and outer zones of commercial and industrial buildings. The theoretical analysis and practical implementation of such systems demonstrate that the coil tube's thermal performance, corrosion resistance, and mechanical integrity are critical to achieving optimal energy efficiency and long-term reliability in hydronic heating and cooling loops.
2. Material & Properties
2.1 Base Material Grades
- Austenitic Stainless Steel: SUS304 / ASTM 304 — General-purpose grade with excellent corrosion resistance, formability, and weldability.
- High-Nickel Austenitic Stainless Steel: SUS316 / ASTM 316 — Enhanced resistance to chloride-induced pitting and crevice corrosion; suitable for coastal or chemically aggressive environments.
- Low-Carbon Austenitic Stainless Steel: SUS304L / ASTM 304L — Reduced carbon content for superior weldability and resistance to intergranular corrosion in sensitized weld zones.
- Super-Austenitic Stainless Steel: SUS316L / ASTM 316L — Low-carbon variant of 316 with outstanding resistance in high-temperature and corrosive service conditions.
2.2 Key Physical & Mechanical Properties
- Density: 7.93 g/cm³ (7,930 kg/m³)
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
- Specific Heat Capacity: 500 J/(kg·K) at 20°C
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /K (20–100°C)
- Tensile Strength (UTS): ≥ 520 MPa (SUS304); ≥ 515 MPa (SUS316)
- Yield Strength (0.2% Proof): ≥ 205 MPa (SUS304); ≥ 205 MPa (SUS316)
- Elongation at Break: ≥ 40% (minimum)
- Hardness (Rockwell B): ≤ 95 HRB (annealed condition)
2.3 Corrosion Resistance Characteristics
The passive chromium oxide film (Cr₂O₃) formed on the surface provides inherent protection against atmospheric corrosion. In SUS316 and SUS316L grades, the addition of 2.0–3.0% Molybdenum (Mo) significantly improves resistance to localized corrosion in chloride-containing environments. The products comply with standard corrosion testing protocols including:
- ASTM G48: Pitting and Crevice Corrosion in 6% Ferric Chloride Solution
- ASTM A967: Passivation of Stainless Steel Parts
- ISO 3506: Corrosion Testing in Laboratory Atmospheres
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm – Φ50.8 mm (custom ranges available) | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A213 / EN 10216-5 |
| Coil Inner Diameter (ID) | Φ150 mm – Φ600 mm | Manufacturer Standard |
| Coil Length (per coil) | 50 m – 300 m (negotiable) | — |
| Surface Finish | 2B (Cold-Rolled & Annealed), BA (Bright Annealed), No.4 Brushed, Mirror (8K) | ASTM A480 / GB/T 3280 |
| Tolerance on OD | ±0.05 mm (precision grade); ±0.10 mm (commercial grade) | ASTM A213 / EN 10216-5 |
| Tolerance on Wall Thickness | ±10% (commercial); ±5% (precision) | ASTM A213 |
| Operating Temperature Range | −196°C to +870°C (SUS304/316); −196°C to +925°C (SUS316L) | ASME BPVC Section II |
| Maximum Working Pressure | Dependent on OD, wall thickness, and grade; typically up to 1.6 MPa (16 bar) for standard HVAC service | EN 10216-5 / ASME B31.9 |
| End Condition | Plain cut, beveled, or threaded (on request) | — |
| Chemical Composition (SUS304) | C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, Cr 18.0–20.0%, Ni 8.0–10.5%, P ≤ 0.045%, S ≤ 0.030% | ASTM A240 / JIS G4305 |
| Chemical Composition (SUS316) | C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, P ≤ 0.045%, S ≤ 0.030% | ASTM A240 / JIS G4305 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: High-purity stainless steel strip or seamless pipe blanks procured from certified mills, verified via spectroscopic analysis (OES — Optical Emission Spectrometry) for chemical composition compliance.
- Cold Rolling & Annealing: Strip is cold-rolled to precise thickness and subsequently annealed in a controlled atmosphere (nitrogen or vacuum) to achieve the desired grain structure and mechanical properties.
- Coil Forming (Tube Drawing & Forming): Flat strip is formed into tubular cross-section using precision roll-forming dies. For seamless coil tubes, the process involves cold-drawing through a die to achieve the required OD and wall thickness.
- Welding (if applicable): For welded coil tubes, TIG (Tungsten Inert Gas) welding or laser welding is employed with argon shielding to maintain a clean, oxidation-free weld seam. Weld seam quality is verified by 100% eddy current inspection.
- Coiling: The formed tube is wound onto a precision mandrel to create the final coil geometry. Tension-controlled coiling ensures uniform curvature and prevents kinking or flattening.
- Surface Treatment: Pickling and passivation treatment removes mill scale and surface contaminants, restoring the passive chromium oxide film for maximum corrosion resistance.
- Quality Inspection: Each coil undergoes dimensional verification (OD, wall thickness, coil ID), visual inspection, and non-destructive testing (NDT) including eddy current and hydrostatic pressure testing.
- Packaging & Shipping: Coils are wrapped in protective plastic film, banded with steel strapping, and placed on wooden pallets or custom steel crates for international shipping.
4.2 Process Control Parameters
- Annealing Temperature: 1050–1150°C for solution treatment, followed by controlled cooling rate ≤ 50°C/min
- Forming Reduction Ratio: 30–60% per pass, depending on material grade and target dimensions
- Hydrostatic Test Pressure: 1.5 × maximum working pressure, held for minimum 5 seconds
- Surface Roughness (Ra): ≤ 1.6 μm (2B finish); ≤ 0.4 μm (BA finish); ≤ 0.2 μm (Mirror finish)
5. Applications
5.1 HVAC Systems (Primary Application Domain)
The coil tube is a core component in Two-Pipe Fan Coil Units (FCUs) integrated with fresh air supply systems for air-conditioned buildings. The theoretical analysis and practical implementation of such systems (二管制风机盘管加新风系统兼用于空调内外区) demonstrate that:
- The coil tube serves as the heat exchange medium in hydronic cooling/heating loops, transferring thermal energy between the circulating fluid (water or glycol) and the ambient air drawn across the coil by a fan.
- In dual-zone configurations (inner and outer zones of a building), the coil tube's uniform heat transfer characteristics enable simultaneous heating and cooling operations, improving occupant comfort and energy efficiency.
- The stainless steel material eliminates the risk of internal corrosion, scale formation, and fouling that would degrade heat transfer performance over time — a critical advantage over carbon steel alternatives in long-term service.
5.2 Additional Application Areas
- Industrial Process Heating & Cooling: Heat exchangers, condensers, evaporators, and radiators in chemical, pharmaceutical, and food processing industries.
- Refrigeration & Cryogenics: Refrigerant coils for commercial refrigeration units, cold storage facilities, and cryogenic equipment (SUS304/316 grades with proven low-temperature toughness down to −196°C).
- Building Services: Radiator tubes, underfloor heating loops, and plumbing systems requiring corrosion-resistant, hygienic piping.
- Marine & Offshore: Seawater cooling coils, ballast water system components, and desalination plant heat exchangers (SUS316/316L grades preferred for chloride resistance).
- Medical & Laboratory: Equipment housings, fluid delivery lines, and sterilizable process loops requiring biocompatible, non-toxic materials.
- Automotive & Transportation: Exhaust system components, fuel lines, and thermal management systems in high-performance and electric vehicles.
6. Quality Certifications & Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- CE Marking — Conformity with European Union directives for pressure equipment (PED 2014/68/EU)
- EN 10204 3.1 — Inspection Certificate issued by authorized quality inspector
- Mill Test Certificate (MTC) — Provided per shipment, including chemical analysis and mechanical test results
6.2 Standards Compliance
| Standard | Scope of Compliance |
|---|---|
| ASTM A213 / A269 | Austenitic stainless steel seamless and welded tubes for boiler, heat exchanger, and general heat transfer service |
| EN 10216-5 | Non-alloy and alloy steel tubes for pressure purposes — austenitic stainless steel |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for fluid conveyance |
| JIS G4305 | Japanese Industrial Standard for austenitic stainless steel tubes |
| ASME SA-213 / SA-269 | American Society of Mechanical Engineers standard for austenitic stainless steel tubes |
| NSF/ANSI 61 | Drinking water system components — health effects (where applicable for potable water service) |