Stainless Steel Coil Tube (Coil Tube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (also referred to as 盘管 / Coil Tube) is a precision-engineered heat transfer component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed for use in coil-type condensers, evaporators, and various heat exchange systems where compact geometry, high thermal efficiency, and corrosion resistance are critical performance parameters. The coil tube represents a helically wound continuous tube configuration that offers superior heat transfer characteristics compared to traditional straight-tube arrangements, particularly in shell-and-coil condenser applications.
Based on comparative experimental research between coil-type condensers and shell-and-tube condensers, coil tubes demonstrate distinct advantages in terms of heat transfer coefficient enhancement, reduced pressure drop, and compact volumetric design. These properties make the stainless steel coil tube an ideal selection for demanding industrial and commercial refrigeration, HVAC, and chemical processing applications.
2. Material & Properties
2.1 Base Material Grades
- ASTM A269 / AMS 5663 — Primary specification for stainless steel seamless and welded tubing
- Grade 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- Grade 316 (UNS S31600) — Enhanced corrosion resistance with molybdenum addition for chloride-rich environments
- Grade 316L (UNS S31603) — Low-carbon variant suitable for welding applications requiring reduced sensitization risk
- Grade 321 (UNS S32100) — Titanium-stabilized grade for high-temperature service
2.2 Mechanical Properties (Typical — Grade 304)
| Property | Specification | Unit |
|---|---|---|
| Tensile Strength (Minimum) | ≥ 515 | MPa |
| Yield Strength (0.2% Offset, Minimum) | ≥ 205 | MPa |
| Elongation (in 50 mm gauge length, Minimum) | ≥ 40 | % |
| Density | 8.00 | g/cm³ |
| Thermal Conductivity (at 20°C) | 16.3 | W/(m·K) |
| Thermal Conductivity (at 100°C) | 16.3 | W/(m·K) |
| Thermal Conductivity (at 500°C) | 21.5 | W/(m·K) |
| Coefficient of Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ | 1/K |
| Specific Heat Capacity (at 20°C) | 500 | J/(kg·K) |
| Maximum Service Temperature | 870 | °C |
| Minimum Service Temperature | -196 | °C (Cryogenic capable) |
2.3 Chemical Composition (ASTM A269 — Grade 304)
| Element | Maximum (%) | Element | Specification (%) |
|---|---|---|---|
| Carbon (C) | 0.08 | Chromium (Cr) | 18.00 – 20.00 |
| Nickel (Ni) | 8.00 – 10.50 | Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 | Sulfur (S) | ≤ 0.030 |
| Silicon (Si) | ≤ 1.00 | Iron (Fe) | Balance |
2.4 Key Material Advantages
- Corrosion Resistance: The chromium oxide passive film provides inherent resistance to atmospheric, chemical, and aqueous corrosion
- Magnetic Properties: Non-magnetic in annealed condition, suitable for sensitive instrumentation environments
- Hygienic Surface: Achievable surface roughness as low as Ra ≤ 0.4 μm for pharmaceutical and food-grade applications
- Weldability: Excellent welding characteristics with minimal post-weld treatment required (especially Grade 316L)
- Formability: Superior cold-working capability enabling tight coil winding radii without cracking
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 50.8 mm (1/8" – 2") | ASTM A269 / EN 10217 |
| Wall Thickness | 0.3 mm – 3.0 mm | ASTM A269 |
| Coil Winding Diameter | 50 mm – 500 mm (adjustable per application) | Custom / Client-Specified |
| Coil Pitch (Helical Spacing) | 10 mm – 50 mm | Custom / Client-Specified |
| Coil Length (Unwound) | 3 m – 50 m (standard); up to 200 m (custom) | — |
| Minimum Bending Radius | ≥ 3D (D = outer diameter) | ASTM A269 |
| Dimensional Tolerance (OD) | ± 0.05 mm (precision); ± 0.1 mm (standard) | ASTM A269 / AMS 5663 |
| Dimensional Tolerance (Wall Thickness) | ± 10% of nominal | ASTM A269 |
| Surface Finish | Ba & Le (Bright & Annealed); No. 4; Electropolished (Ra ≤ 0.4 μm) | ASTM A269 |
| End Condition | Plain, threaded, flanged, or custom fittings | ASME B1.20.1 / B16.11 |
3.2 Performance Characteristics (Coil-Type Condenser Configuration)
| Performance Parameter | Coil-Type Condenser | Shell-and-Tube Condenser | Relative Advantage |
|---|---|---|---|
| Heat Transfer Coefficient | 1,200 – 2,500 W/(m²·K) | 800 – 1,800 W/(m²·K) | Coil type: +30% to +60% |
| Pressure Drop (per unit length) | Lower (smooth helical flow) | Higher (turbulent tube-side) | Coil type: -15% to -35% |
| Specific Surface Area (m²/m³) | 150 – 350 | 80 – 200 | Coil type: +75% to +100% |
| Footprint Efficiency | High (compact helical geometry) | Lower (larger shell diameter) | Coil type: -20% to -40% volume |
| Maintenance Accessibility | Coil removable as single unit | Tube cleaning requires pulling | Coil type: Easier inspection |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection: Certified stainless steel seamless or welded tube stock procured in compliance with ASTM A269, AMS 5663, or EN 10217-7. Incoming material undergoes spectroscopic analysis (PMI — Positive Material Identification), dimensional verification, and visual inspection.
- Cold Drawing / Precision Sizing: Tube stock is cold-drawn to achieve precise dimensional tolerances and enhanced mechanical properties. Multiple drawing passes ensure uniform wall thickness and roundness.
- Heat Treatment (Annealing): Solution annealing at 1050–1150°C followed by controlled cooling to achieve the desired microstructure, relieve residual stresses, and restore full corrosion resistance. For Grade 316L, annealing at 1050°C is standard.
- Precision Coil Winding: The annealed tube is helically wound using CNC-controlled coil winding machinery to achieve exact winding diameter, pitch, and number of turns. The winding process is programmed to avoid kinking, ovality, or wall thinning at bend locations.
- End Fitting & Connection: Tube ends are prepared for connection via welding (TIG/Orbital), threading, or flanging depending on the application requirement. All welds are performed in inert gas (argon) atmosphere to prevent oxidation.
- Surface Treatment: Options include passivation (nitric or citric acid), electropolishing (for Ra ≤ 0.4 μm), or passivation + electropolishing combination for maximum surface integrity.
- Non-Destructive Testing (NDT): All welds undergo 100% visual inspection, dye penetrant testing (PT), and hydrostatic pressure testing. Radiographic testing (RT) or ultrasonic testing (UT) available upon request.
- Pressure Testing: Hydrostatic pressure testing at 1.5× working pressure for a minimum of 30 seconds with no leakage or permanent deformation.
- Final Inspection & Packaging: Dimensional verification, surface finish measurement, and certification documentation. Protective end caps and moisture-absorbent packaging for shipment.
4.2 Quality Control Checkpoints
- Incoming material certification (Mill Test Report — MTR) verification
- In-process dimensional monitoring at each winding station
- Post-winding dimensional audit (coil diameter, pitch, total turns)
- 100% hydrostatic pressure test at 1.5× design pressure
- Surface roughness measurement (Ra) for electropolished products
- Corrosion testing (ASTM A967 passivation verification) for all product lots
5. Applications
5.1 Primary Application Areas
- Industrial Refrigeration: Coil-type condensers for ammonia, R-134a, R-410A, and CO₂ transcritical refrigeration systems. The stainless steel construction provides corrosion resistance against ammonia and prevents contamination of refrigerant circuits.
- Heat Exchangers & Chillers: Compact coil heat exchangers for process cooling, chiller condensers, and evaporator coils in industrial cooling systems.
- Chemical Processing: Heat transfer coils for chemical reactors, distillation columns, and process fluid conditioning where resistance to acids, alkalis, and chlorides is required.
- Pharmaceutical & Food Industry: Hygienic-grade coil tubes for pasteurizers, condensers, and CIP (Clean-in-Place) compatible heat exchange systems. Electropolished surfaces prevent bacterial adhesion.
- Power Generation: Condenser coils in cogeneration systems, waste heat recovery units, and small-scale steam condensation systems.
- Cryogenic Applications: Stainless steel coil tubes maintain ductility at cryogenic temperatures (-196°C), suitable for LNG (Liquefied Natural Gas) processing and cryogenic separation.
- Marine & Offshore: Seawater-cooled condensers and heat exchangers where resistance to chloride-induced pitting and crevice corrosion is essential (Grade 316/316L recommended).
- HVAC Systems: Compact coil condensers for commercial air conditioning and heat pump systems requiring high efficiency in limited installation spaces.
5.2 Comparative Advantage in Condenser Applications
Experimental research comparing coil-type condensers with shell-and-tube condensers has demonstrated that coil-type configurations achieve 30–60% higher overall heat transfer coefficients due to the inherent turbulence enhancement from the helical curvature of the tube. The centripetal force generated by the coil geometry promotes secondary flow patterns (Dean vortices) within the tube, effectively disrupting the thermal boundary layer and enhancing convective heat transfer. Additionally, coil-type condensers exhibit 15–35% lower pressure drops compared to equivalent shell-and-tube designs, resulting in improved system COP (Coefficient of Performance) and reduced compressor energy consumption.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Title / Scope | Applicability |
|---|---|---|
| ASTM A269 / A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severities of Service | Primary material specification |
| AMS 5663 | Aerospace Material Specification — Stainless Steel Tubing, Seamless | High-performance applications |
| EN 10217-7 | Non-ferrous metal tubes and profiles |