Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous tube product supplied in coiled form, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for use in HVAC (Heating, Ventilation, and Air Conditioning) systems, particularly in Dry-State Fan Coil Unit (FCU) combined with Fresh Air System configurations. The coiltube serves as the core heat exchange medium, enabling efficient thermal transfer while maintaining low pressure drop and superior hygienic performance under dry operating conditions.
Unlike conventional finned tube assemblies, the stainless steel coiltube offers inherent resistance to corrosion, microbial growth, and scale formation, making it an ideal choice for energy-efficient air conditioning processes where condensation control and indoor air quality (IAQ) are critical design parameters.
2. Material & Properties
2.1 Base Material Composition
The coiltube is fabricated from high-grade austenitic stainless steel, conforming to the following material standards:
- AISI 304 (UNS S30400) — General-purpose corrosion-resistant grade with excellent formability
- AISI 316L (UNS S31603) — Enhanced molybdenum-bearing grade for aggressive environments
- Equivalent Chinese Standards: GB/T 12771, GB/T 14976
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa | ASTM A213 / GB/T 228 |
| Yield Strength (0.2% offset) | ≥ 205 MPa | ASTM A213 / GB/T 228 |
| Elongation at Break | ≥ 40% | ASTM A213 |
| Hardness (HV) | ≤ 220 | ASTM E92 |
| Thermal Conductivity (25°C) | 16.3 W/(m·K) | ASTM E153 |
| Operating Temperature Range | −196°C to +870°C | — |
2.3 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, fresh water, and mild chemical environments
- Resistance to pitting and crevice corrosion (particularly 316L grade) in chlorinated water systems
- No oxidation scaling under normal HVAC operating conditions
- Compliant with NSF/ANSI 61 for potable water contact applications
3. Technical Specifications
| Parameter | Specification / Range | Notes |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.7 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4"), 25.4 mm (1") | Custom sizes available upon request |
| Wall Thickness | 0.5 mm – 3.0 mm | Tolerance: ±0.05 mm |
| Coil Length | 20 m – 200 m per coil | Adjustable based on customer requirement |
| Coil Inner Diameter | 300 mm – 800 mm | Standard shipping coil ID: 500 mm |
| Surface Finish | Bright annealed / Polished (Ra ≤ 0.4 μm) | Low roughness for reduced fouling |
| End Condition | Plain / Beveled / Threaded / Flanged | Custom end preparation available |
| Max. Operating Pressure | 1.6 MPa (standard); 4.0 MPa (reinforced) | Hydrostatic test at 1.5× working pressure |
| Dimensional Tolerance | OD: ±0.1 mm; Wall: ±0.05 mm | Per ASTM A213 Class 1 |
| Heat Exchange Efficiency | U-value: 800–1500 W/(m²·K) | Dependent on flow regime and fin configuration |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Selection: Sourced from certified stainless steel mills (e.g., Outokumpu, POSCO, Taigang) with full mill test certificates (MTC) per EN 10204 3.1.
- Hot Rolling & Annealing: Billet or strip material is hot-rolled to approximate dimensions, followed by solution annealing at 1050°C – 1100°C in protective atmosphere to achieve full austenitic microstructure.
- Tube Forming (Seamless or Welded): Seamless tubes produced via pierce-rolling or capillary method; welded tubes via TIG (Tungsten Inert Gas) or EFW (Electric Resistance) welding with full-penetration welds.
- Cold Drawing / Mandrel Drawing: Tubes are cold-drawn over tungsten carbide dies to achieve precise dimensional tolerances and improved surface finish.
- Intermediate Annealing: Periodic annealing cycles to relieve cold-work hardening and maintain ductility for coil forming.
- Surface Treatment: Pickling and passivation to remove surface contaminants and establish a stable chromium oxide passive film.
- Coil Winding: Tubes are wound into coils using computer-controlled winding machines to ensure uniform coil geometry and prevent mechanical damage.
- Quality Inspection & Packaging: Each coil undergoes dimensional verification, visual inspection, and pressure testing before protective packaging.
4.2 Key Process Controls
- Grain Size Control: Annealing parameters optimized to achieve grain size 6–8 (ASTM E112), ensuring good fatigue resistance
- Intergranular Corrosion Resistance: Carbon content ≤ 0.03% (L-grade) or stabilized grades to prevent chromium carbide precipitation
- Weld Seam Integrity: 100% eddy current testing (ECT) or ultrasonic testing (UT) on welded tubes
- Surface Roughness: Monitored via laser profilometry; target Ra ≤ 0.4 μm for reduced biofilm adhesion
5. Applications
5.1 Primary Application — HVAC Systems
The stainless steel coiltube is the principal heat transfer component in Dry-State Fan Coil Unit (FCU) plus Fresh Air System configurations. In this design paradigm:
- The FCU operates in dry mode (sensible cooling only), where the coil surface temperature remains above the dew point of the supply air, eliminating condensation formation
- Moisture removal is handled by a dedicated fresh air handling unit with deep dehumidification capability
- This separation of sensible and latent loads enables superior indoor air quality, reduced energy consumption, and elimination of microbial growth on coil surfaces
- The stainless steel coiltube's smooth surface and corrosion resistance make it particularly well-suited for this application, as it prevents the biofilm formation and corrosion pitting associated with traditional carbon steel coils in cyclic wet-dry environments
5.2 Additional Applications
- Commercial Building HVAC: Chilled water coils in medium and large-scale air conditioning systems
- Food & Beverage Industry: Heat exchangers, pasteurization coils, and hygienic process piping (3-A sanitary grade available)
- Pharmaceutical Manufacturing: CIP (Clean-In-Place) compatible coil assemblies for GMP environments
- Marine & Coastal Applications: Seawater-cooled heat exchangers leveraging 316L grade pitting corrosion resistance
- Geothermal Systems: Ground source heat exchanger loops operating in closed-loop configurations
- Industrial Process Cooling: Precision temperature control in semiconductor fabrication, laser processing, and chemical reactors
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ASME B31.5 | Pressure Piping — Process Piping |
| ASTM A213 / A269 | Standard Specifications for Seamless & Welded Austenitic Stainless Steel Tubing |
| GB/T 12771-2019 | Chinese National Standard — Seamless Stainless Steel Tubes |
| EN 10216-5 | European Standard — Welded Stainless Steel Tubes |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects |
| CE Marking | European Conformity — Pressure Equipment Directive (PED 2014/68/EU) |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 — Chemical & Mechanical Analysis |
7. Unique Selling Points (USPs)
- Superior Hygienic Performance: The polished stainless steel surface (Ra ≤ 0.4 μm) minimizes bacterial adhesion and biofilm formation, critical for dry-state HVAC applications where coil surfaces are never fully drained
- Exceptional Service Life: 25–50 year design life with no degradation of mechanical or thermal properties under normal HVAC operating conditions — significantly outperforming copper and carbon steel alternatives
- Thermal Stability in Dry-State Operation: Maintains consistent heat transfer coefficients without the fouling and scale buildup that degrades traditional coil performance over time
- Full Traceability: Each coil is traceable to its mill heat number with complete chemical and mechanical test data, enabling rigorous quality assurance in regulated industries
- Customization Flexibility: Available in a wide range of diameters, wall thicknesses, and coil lengths to accommodate specific system design requirements from residential to large commercial installations
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, contributing to green building certification credits (LEED, BREEAM, CASBEE)
Design Note: In the context of the dry-state FCU plus fresh air system, the stainless steel coiltube enables a system architecture where the sensible cooling load is handled by the dry FCU coil while the latent (dehumidification) load is managed by a separate fresh air unit. This decoupled approach, combined with the corrosion-resistant and hygienic properties of stainless steel, results in a system that achieves energy savings of 15%–30% compared to conventional all-coil systems while delivering superior indoor air quality and occupant comfort.
8. Ordering Information
Customers are advised to specify the following parameters when placing orders:
- Material grade (AISI 304 / 316L / custom)
- Outer diameter and wall thickness (with tolerance requirements)
- Required coil length and coil inner diameter
- Surface finish requirement (bright annealed / polished / sanitary grade)
- End condition (plain / beveled / threaded / flanged)
- Applicable standard and certification requirements
- Intended application and operating conditions
Wenzhou Jixing Metal Materials Co., Ltd. offers comprehensive technical support, sample provision, and custom engineering consultation for all coiltube products. Contact the sales engineering team for detailed quotations and application-specific design assistance.