Stainless Steel Coil Tube (Coiltube) — Hospital HVAC Antibacterial Application Series
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1191), this stainless steel coil tube is engineered specifically for dry-coil air conditioning systems deployed in hospital wards and other high-hygiene environments. The product line addresses critical requirements for antimicrobial performance, corrosion resistance, and thermal efficiency in sensitive clinical infrastructure, drawing upon research findings related to hospital ward anti-SARS antibacterial dry coil tube air conditioning system studies.
1. Product Overview
The stainless steel coil tube (Coiltube) is a precision-manufactured tubular product formed into continuous coil configurations, designed primarily for use in evaporator coils, condenser coils, and heat exchange assemblies within commercial and medical HVAC (Heating, Ventilation, and Air Conditioning) systems. Unlike conventional carbon steel or copper tubing, this stainless steel variant offers superior resistance to biofilm formation, microbial colonization, and chemical degradation — making it particularly suitable for hospital ward environments where airborne pathogen control is paramount.
The product is supplied in continuous coil (spool) form, enabling downstream fabricators to cut and form tubes to exact specifications without generating weld seams or end-joint vulnerabilities that could compromise system integrity or serve as bacterial harborage sites.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, meeting or exceeding the following material standards:
- Base Alloy: AISI 304 / AISI 316L stainless steel (per ASTM A213 / ASTM A269)
- Chromium Content (Cr): ≥ 18% (provides passive oxide layer for corrosion resistance)
- Nickel Content (Ni): ≥ 8% (stabilizes austenitic microstructure)
- Molybdenum Content (Mo): ≥ 2.0% (in 316L grade; enhances pitting and crevice corrosion resistance)
- Carbon Content (C): ≤ 0.03% (low-carbon "L" grade minimizes intergranular corrosion risk)
- Surface Finish: Electropolished or passivated interior surface (Ra ≤ 0.4 μm) to inhibit biofilm adhesion
Key Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (AISI 304); ≥ 485 MPa (AISI 316L)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (HB): 120–180 (annealed condition)
- Operating Temperature Range: −196 °C to +870 °C
- Thermal Conductivity: 14.5–16.3 W/(m·K)
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 25.4 mm (¼" – 1") | ASTM A213 / A269 |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm (0.020" – 0.079") | ASTM A269 |
| Coil Length (per spool) | 100 m – 600 m (configurable) | Manufacturer specification |
| Coil Inner Diameter (ID) | 300 mm – 800 mm | Manufacturer specification |
| Surface Roughness (interior) | Ra ≤ 0.4 μm (electropolished) | ISO 4287 |
| Surface Roughness (exterior) | Ra ≤ 1.6 μm (pickled & passivated) | ISO 4287 |
| Pressure Rating | Up to 1.6 MPa (232 psi) at ambient temperature | ASME B31.5 |
| Material Grade Options | AISI 304 / 304L / 316 / 316L | ASTM A213 / A269 |
| Heat Treatment Condition | Annealed (Solution Treated) | ASTM A213 |
| End Treatment | Plain end / Beveled end / Formed end (per customer spec) | Customer requirement |
| Coating / Treatment | Passivation (Nitric acid or Citric acid based) | ASTM A967 / A380 |
| Antimicrobial Treatment | Optional: Silver-ion (Ag⁺) surface functionalization | ISO 22196 |
| Hydrostatic Test Pressure | 1.5× working pressure | ASME B31.5 |
| Packaging | Wooden reel / Steel drum with moisture-proof wrapping | ISO 4180 |
4. Manufacturing Process
The production of this stainless steel coil tube follows a multi-stage precision manufacturing process:
- Material Selection & Incoming Inspection: Hot-rolled stainless steel strip is procured from certified mills (e.g., Outokumpu, POSCO, Baowu) and subjected to spectroscopic verification (OES analysis) to confirm alloy composition compliance.
- Slitting & Leveling: The strip is slit to precise width and leveled to ensure dimensional consistency and flatness prior to forming.
- Forming (Seamless or Welded):
- Seamless route: The strip is wrapped around a mandrel and cold-rolled through a series of reducing rolls to achieve the target OD and wall thickness.
- Welded route: The strip is formed into a tube blank and welded via TIG (Tungsten Inert Gas) welding with 100% helium leak detection (helium partial pressure ≤ 1×10⁻⁷ Pa·m³/s).
- Cold Drawing / Precision Sizing: Tubes are drawn through calibrated dies to achieve tight dimensional tolerances (OD tolerance: ±0.05 mm; WT tolerance: ±0.05 mm).
- Heat Treatment (Annealing): Tubes are solution-annealed at 1050–1150 °C followed by rapid water quenching to restore full austenitic microstructure and eliminate cold-work hardening.
- Pickling & Passivation: Surface oxide scale is removed via acid pickling (HNO₃/HF blend or citric acid), followed by passivation to establish a uniform chromium-rich passive film (Cr₂O₃) that provides inherent corrosion resistance.
- Electropolishing (Interior Surface): Selected grades undergo interior electropolishing to achieve Ra ≤ 0.4 μm, critical for minimizing biofilm adhesion in hospital applications.
- Antimicrobial Functionalization (Optional): Silver-ion (Ag⁺) or copper-based antimicrobial coatings may be applied to the interior surface, providing sustained biocidal activity against bacteria (including SARS-CoV-2, E. coli, S. aureus) per ISO 22196 testing protocols.
- Coiling & Packaging: Finished tubes are coiled onto precision-wound reels, protected with moisture-barrier film, and packed for shipment.
5. Applications
- Hospital HVAC Systems: Primary application in dry-coil air conditioning units for hospital wards, ICU (Intensive Care Units), operating theatres, and clean rooms. The antimicrobial surface properties directly address airborne pathogen control requirements identified in research on anti-SARS hospital ventilation systems.
- Pharmaceutical & Biotech Facilities: Cleanroom HVAC coils, CIP (Clean-In-Place) systems, and process piping in GMP-regulated environments.
- Food & Beverage Processing: Heat exchangers, pasteurization coils, and refrigeration systems requiring hygienic-grade tubing.
- Marine & Offshore HVAC: Condenser and evaporator coils in marine air conditioning systems where chloride-induced corrosion is a concern (316L grade recommended).
- Commercial Refrigeration: Cold storage evaporators and display case refrigeration coils.
- Medical Equipment: Tubing components in sterilizable medical devices, dialysis machines, and laboratory equipment.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality management and product certifications:
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 22196 — Antimicrobial Testing (for treated variants)
- EN 10204 3.1 — Material Test Certificates (Mill Test Reports)
- CE Marking — Conformity with European standards for pressure equipment
- ASME Stamp — Where applicable for pressure-containing applications
- RoHS & REACH Compliance — Restriction of hazardous substances for EU market access
- NACE MR0175 — Suitability for sour service (where applicable)
7. Unique Selling Points
- Inherent Antimicrobial Performance: The combination of electropolished surface finish (Ra ≤ 0.4 μm) and optional silver-ion functionalization provides sustained reduction of microbial contamination — validated against SARS-CoV-2 and other respiratory pathogens, directly addressing the concerns raised in academic research on hospital anti-SARS ventilation systems.
- Superior Corrosion Resistance: AISI 316L grade offers exceptional resistance to chlorides, condensation water, and cleaning chemicals commonly encountered in hospital environments.
- Seamless Coil Configuration: Eliminates weld joints along the tube length, reducing potential failure points and eliminating crevices where biofilms can establish.
- Full Traceability: Every coil is traceable to its mill heat number with complete chemical and mechanical test documentation.
- Customization Capability: Flexible OD, wall thickness, coil length, and end-treatment options to meet specific OEM requirements.
- Hygienic Design: Interior surface finish meets FDA 21 CFR Part 178 and EU 1935/2004 food-contact material regulations.
Note: The product development of this coil tube series is informed by research findings from the study titled "Research on Hospital Ward Anti-SARS Antibacterial Dry Coil Tube Air Conditioning System," as well as subsequent academic critiques and validations of that research. Wenzhou Jixing Metal Materials Co., Ltd. continues to invest in R&D to advance antimicrobial stainless steel tubing technology for critical healthcare infrastructure applications.