2. Material & Properties

Stainless steel coil tubes are fabricated from austenitic stainless steel grades, selected for their exceptional resistance to corrosion, high-temperature performance, and mechanical integrity. The primary alloying elements and their contributions are detailed below:

• Chromium (Cr): Minimum 17–22% — forms a passive oxide layer providing superior corrosion resistance
• Nickel (Ni): Minimum 8–10% — enhances ductility and stabilizes the austenitic microstructure
• Molybdenum (Mo): 2–3% (in duplex grades) — improves resistance to pitting and crevice corrosion
• Carbon (C): ≤ 0.08% — limits carbide precipitation at weld joints

Key Mechanical Properties:

• Tensile Strength: 520–720 MPa
• Yield Strength: ≥ 205 MPa
• Elongation at Break: ≥ 40%
• Hardness: 150–250 HB (Brinell)

Thermal Properties:

• Thermal Conductivity: 14–16 W/(m·K) at 20°C
• Specific Heat Capacity: 500 J/(kg·K)
• Operating Temperature Range: −196°C to +870°C

3. Specifications

4. Manufacturing Process

The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, metallurgical integrity, and surface quality:

1. Raw Material Inspection: Ingot certification verification, chemical composition analysis (spectrometric), and mechanical property testing per ASTM A213 requirements.
2. Hot Rolling: Billet reduction to initial tube blank at temperatures exceeding 1100°C to achieve desired grain structure.
3. Piercing & Elongation: Tube blank formation via rotary piercing mills, followed by controlled elongation to achieve target OD.
4. Intermediate Annealing: Solution annealing at 1050–1100°C with rapid quenching to relieve cold-work stresses and restore ductility.
5. Cold Drawing / Rolling: Multi-pass cold reduction to achieve precise final dimensions, wall thickness, and surface finish. This step also imparts beneficial work-hardening.
6. Pickling & Passivation: Removal of surface scale and contamination via hydrofluoric/nitric acid pickling, followed by passivation treatment to restore the protective chromium oxide layer.
7. Final Annealing (if required): Controlled heating and cooling cycle to achieve specified hardness and mechanical properties.
8. Coiling: Precision coiling onto designated core diameters with controlled tension to prevent deformation or ovality.
9. Non-Destructive Testing (NDT): Eddy current testing, hydrostatic pressure testing (2.5× working pressure for 30 seconds minimum), and visual inspection of all surfaces.
10. Packaging: Protective wrapping, moisture barrier packaging, and labeling with full traceability documentation.

5. Applications

Stainless steel coil tubes manufactured by Wenzhou Jixing Metal Materials Co., Ltd. are engineered for critical thermal management applications, including but not limited to:

• Fan Coil Units (FCUs): Primary heat exchanger coils in commercial HVAC systems for hotels, offices, hospitals, and residential complexes. The coil tube geometry enables maximum surface-area-to-volume ratio for efficient air-side and fluid-side heat transfer.
• Air Conditioning Systems: Evaporator and condenser coils in split systems, rooftop units, and chiller applications.
• Refrigeration Systems: Heat exchangers in industrial refrigeration, cold storage, and process cooling applications.
• Boiler & Heating Systems: Water-to-air heat exchangers in hydronic heating and radiant floor systems.
• Food & Beverage Industry: Sanitary-grade heat exchange coils meeting FDA and EHEDG requirements (SUS316L grade).
• Chemical Processing: Corrosive-environment heat exchangers where resistance to chlorides and acids is critical.
• Marine & Offshore: Seawater-cooled heat exchangers requiring resistance to marine biofouling and chloride-induced pitting.

6. Maintenance & Service Considerations

Based on industry best practices for fan coil unit maintenance, the following guidelines apply to stainless steel coil tubes:

• Periodic Inspection: Visual examination for signs of corrosion, mechanical damage, or refrigerant leakage at a minimum frequency of 12 months.
• Chemical Cleaning: Coil fins and tubes should be cleaned using approved non-abrasive chemical solutions to remove accumulated dust, mold, and biological growth without compromising the passive oxide layer.
• Hydrostatic Testing: Recommended every 5 years or after any major system modification to verify structural integrity.
• Refrigerant Charge Verification: Periodic measurement of subcooling/superheat to detect gradual refrigerant loss indicating tube degradation.
• Flow Rate Monitoring: Ensure proper fluid circulation rates to prevent localized overheating and thermal stress accumulation.

7. Quality Certifications & Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality certifications and compliance standards:

• ISO 9001:2015 — Quality Management System certification
• ISO 14001:2015 — Environmental Management System certification
• ISO 45001:2018 — Occupational Health and Safety Management System
• CE Marking — Conformity with European Directive requirements
• TÜV Rheinland — Third-party product certification
• SGS Testing — Independent material and dimensional verification
• ASTM A213 Compliance — Seamless and welded austenitic stainless steel tubes for heat exchangers
• GB/T 14976 — Chinese national standard for cold-rolled stainless steel seamless tubes

Each production batch is accompanied by a Mill Test Certificate (MTC) documenting chemical composition, mechanical properties, and heat number traceability in accordance with EN 10204 Type 3.1 requirements.

8. Unique Selling Points

• Extended Service Life: Superior corrosion resistance compared to copper or aluminum alternatives, particularly in humid or chemically aggressive environments typical of hotel and commercial HVAC installations.
• Hygienic Performance: Smooth internal bore surface (Ra ≤ 0.4 μm) prevents biofilm accumulation, critical for food-grade and pharmaceutical applications.
• Thermal Stability: Maintains dimensional integrity and mechanical properties across wide temperature excursions without fatigue degradation.
• Full Traceability: Complete material pedigree from raw ingot to finished coil, enabling compliance with international procurement and regulatory requirements.
• Custom Engineering: Capability to produce non-standard OD, wall thickness, and coil configurations to meet specific OEM design requirements.

Note: This specification is intended for technical reference and procurement purposes. For project-specific applications, consult Wenzhou Jixing Metal Materials Co., Ltd. engineering team for detailed design support and material selection guidance.