Stainless Steel Coil Tube (Coiltube) — Antibacterial HVAC Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous stainless steel tubing product designed for use in heating, ventilation, and air conditioning (HVAC) systems, particularly in healthcare and cleanroom environments. This product category encompasses pre-formed coil tubes that are manufactured to exacting dimensional tolerances and surface finish standards, enabling their deployment in critical applications such as hospital ward air conditioning systems, medical gas distribution, and pharmaceutical process piping.
Building upon research documented in the study "Research on Antibacterial Coil Tube Air Conditioning Systems for Hospital Wards to Prevent SARS", this product line has been optimized for applications requiring antimicrobial surface properties, resistance to cross-contamination, and long-term structural integrity under cyclic thermal and mechanical loading conditions. The coil tube form factor offers advantages in storage, transportation, and on-site installation efficiency compared to straight-length tubing.
Material & Properties
Base Alloy Composition
The coil tubes are manufactured from austenitic stainless steel grades, with the following primary options available:
- AISI 304 (UNS S30400) — Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5%; general-purpose corrosion resistance
- AISI 316 (UNS S31600) — Chromium (Cr) 16–18%, Nickel (Ni) 10–14%, Molybdenum (Mo) 2–3%; enhanced resistance to chlorides and hospital disinfectants
- AISI 316L (UNS S31603) — Low-carbon variant of 316 with Carbon (C) ≤ 0.03%; superior weldability and resistance to intergranular corrosion
- AISI 321 (UNS S32100) — Titanium-stabilized grade for elevated temperature service
Key Mechanical & Physical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75,000 psi) | ASTM A270 / GB/T 12771 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,700 psi) | ASTM A270 / GB/T 12771 |
| Elongation at Break | ≥ 35% | ASTM A270 / GB/T 12771 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A270 |
| Density | 8.0 g/cm³ | — |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | — |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /°C | — |
| Corrosion Resistance (Pitting) | PREN ≥ 24 (for 316L grade) | ASTM G48 |
Surface Characteristics
- Surface Roughness (Ra): ≤ 0.4 μm for sanitary/polished finish; ≤ 0.8 μm for standard finish
- Surface Treatment Options: Electropolishing, mechanical polishing, passivation (citric acid or nitric acid), and antibacterial coating (silver-ion infused surface treatment)
- Passivation Film: Self-forming chromium oxide (Cr₂O₃) passive layer, ≥ 3 nm thickness, providing inherent corrosion and microbial resistance
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.175 mm – 114.3 mm (⅛" – 4") | ASTM A270 / GB/T 12771 |
| Wall Thickness (WT) | 0.25 mm – 6.0 mm (0.010" – 0.236") | ASTM A270 / GB/T 12771 |
| OD Tolerance | ± 0.02 mm (for OD ≤ 12.7 mm); ± 0.05% (for OD > 12.7 mm) | ASTM A270 |
| Wall Thickness Tolerance | ± 10% (for WT ≤ 1.0 mm); ± 5% (for WT > 1.0 mm) | ASTM A270 |
| Coil Core Diameter | 150 mm – 400 mm (6" – 16") | — |
| Maximum Coil Length | Up to 200 m (656 ft) per coil | — |
| Maximum Coil Weight | Up to 500 kg (1,100 lbs) per coil | — |
| Operating Temperature Range | −196°C to +870°C (−321°F to +1,598°F) | ASTM A270 |
| Operating Pressure (typical) | Up to 16 bar (232 psi) — depends on OD/WT combination | ASME B31.3 |
| End Condition | Plain, beveled, or thread-forming | — |
| Welding Compatibility | Orbital TIG (Tungsten Inert Gas), laser welding, resistance welding | ASME BPE / ISO 15530 |
Manufacturing Process
The production of precision stainless steel coil tubes follows a multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Hot-rolled stainless steel strip or seamless tube blanks are sourced from certified mills with full chemical composition traceability (mill test certificates per EN 10204 Type 3.1).
- Cold Drawing / Cold Forming: The tube is drawn through precision tungsten carbide or diamond dies to achieve exact OD and wall thickness specifications. Multiple drawing passes are employed for high-precision products.
- Intermediate Annealing: When required to relieve accumulated cold work, the tube undergoes controlled atmosphere annealing at 1050–1150°C followed by controlled cooling to restore ductility and recrystallize the grain structure.
- Precision Sizing & Straightening: Final sizing is performed through calibration rollers or mandrel drawing to achieve tight dimensional tolerances.
- Surface Finishing: The tube interior and exterior are subjected to electropolishing (removing 10–20 μm of surface layer) or mechanical polishing to achieve the required surface roughness. Passivation is applied using citric acid (preferred for medical applications) or nitric acid solutions.
- Antibacterial Treatment (Optional): For healthcare applications, a silver-ion (Ag⁺) antimicrobial coating or nano-silver composite layer may be applied to the inner surface, providing sustained release of antimicrobial ions against bacteria including Mycobacterium tuberculosis, Staphylococcus aureus, and Escherichia coli.
- Coiling & Packaging: The finished tube is coiled around a protective core, wrapped in anti-corrosion paper or polyethylene film, and secured with stainless steel strapping. Each coil is labeled with heat number, dimensions, grade, and lot traceability information.
- Quality Inspection: 100% inspection for dimensional compliance, plus sampling for chemical analysis, mechanical testing, hydrostatic pressure testing, and surface finish verification.
Applications
Healthcare & Medical Facilities
- Hospital ward HVAC coil tubes for infection control (SARS, COVID-19, and other airborne pathogen mitigation)
- Operating room (OR) ventilation and cleanroom air distribution systems
- Medical gas supply piping (oxygen, nitrogen, medical air, vacuum)
- Pharmaceutical cleanroom piping per ISO 14644 cleanroom classification standards
Industrial & Process Engineering
- Food and beverage processing equipment (dairy, brewing, juice processing)
- Chemical process piping and heat exchanger tubes
- Automotive fuel and exhaust system components
- Oil and gas downstream processing
Building Services
- Commercial HVAC chilled water and hot water coil tubes
- Domestic hot water recirculation systems
- Radiant heating floor systems
Quality Certifications & Standards Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| ASTM A270 / A269 | Standard specification for austenitic stainless steel seamless, welded, and heavily cold-worked tubing |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes |
| EN 10217-7 | European standard for seamless austenitic stainless steel tubes |
| ASME BPE | BioPharmaceutical Equipment and Systems (for pharmaceutical-grade applications) |
| NSF/ANSI 61 | Drinking water system components — health effects |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance (where applicable) |
| EN 10204 Type 3.1 | Material inspection documents (test reports based on specific inspection) |
Unique Selling Points
1. Proven Healthcare Infection Control Performance: Validated through research on antibacterial coil tube HVAC systems for hospital wards, demonstrating effective pathogen mitigation including resistance against SARS-CoV-related aerosol transmission pathways.
2. Precision Coil Form Factor: Continuous coil delivery eliminates field splices, reduces installation labor by up to 40%, and minimizes potential leak points in critical applications.
3. Dual Protection Architecture: Combines the inherent passive corrosion resistance of austenitic stainless steel with optional active antimicrobial surface treatment for comprehensive microbial defense.
4. Full Traceability: Every coil is traceable to its heat number, chemical composition, mechanical test results, and surface treatment batch, ensuring complete supply chain accountability.
5. Multi-Grade Flexibility: Availability in 304, 316, 316L, and 321 grades allows engineers to optimize material selection based on service environment, cost, and performance requirements.
Technical Notes & Installation Guidance
- Coil tubes should be stored in a dry, indoor environment away from direct contact with carbon steel to prevent galvanic contamination.
- During installation, use only stainless steel or compatible tools to avoid iron contamination of the passive surface.
- Welding of coil tube assemblies should be performed using orbital TIG welding with argon (Ar) internal purge gas at a minimum flow rate of 0.5 L/min to maintain interior surface quality.
- Post-installation passivation is recommended for systems exposed to aggressive water chemistry or chlorinated disinfectants.
- For HVAC coil applications, a minimum water velocity of 0.5 m/s is recommended to prevent sedimentation and biofilm formation.