Stainless Steel Coil Tube (Coiltube) — HVAC Fresh Air Unit Series
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., the Stainless Steel Coil Tube is a precision-engineered tubular component designed for integration into fresh air handling units (Fresh Air Units, FAUs), heat exchangers, and thermal energy transfer systems. This product represents a critical component in the HVAC (Heating, Ventilation, and Air Conditioning) industry, engineered to withstand demanding thermal cycling conditions while maintaining structural integrity and corrosion resistance over extended service life.
Product Overview
The Stainless Steel Coil Tube is supplied in continuous coil form, allowing downstream manufacturers to cut, bend, and form the tubing to precise configurations required for fin-and-tube heat exchanger assemblies, evaporator coils, condenser coils, and fresh air unit heat recovery modules. The coil form factor provides significant advantages in terms of material utilization efficiency, reduced waste during fabrication, and consistent mechanical properties along the entire length of the tube.
This product is specifically engineered with consideration for freeze protection mechanisms and anti-freeze performance, addressing the well-documented risk of coil tube rupture caused by ice formation and hydraulic expansion in cold-climate HVAC applications. The design philosophy incorporates enhanced wall thickness tolerances, optimized thermal conductivity, and material selection criteria that collectively mitigate the freeze-induced failure modes identified in industry research on fresh air unit coil freezing mechanisms.
Material & Properties
Base Material Specification
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to international material standards. The primary material grades offered include:
- ASTM A269 / ASTM B462 — Standard austenitic stainless steel seamless and welded tubing
- EN 10216-5 — European standard for austenitic stainless steel tubing
- JIS G3459 — Japanese Industrial Standard for austenitic stainless steel tubing
Chemical Composition (Typical — Grade 304/06Cr19Ni10)
| Element | Specification |
|---|---|
| Carbon (C) | ≤ 0.08% |
| Chromium (Cr) | 18.00% – 20.00% |
| Nickel (Ni) | 8.00% – 10.50% |
| Manganese (Mn) | ≤ 2.00% |
| Silicon (Si) | ≤ 0.75% |
| Phosphorus (P) | ≤ 0.035% |
| Sulfur (S) | ≤ 0.030% |
| Nitrogen (N) | ≤ 0.030% |
| Iron (Fe) | Balance |
Mechanical & Physical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa (75,400 psi) | ASTM A269 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,730 psi) | ASTM A269 |
| Elongation (at Break) | ≥ 40% | ASTM A269 |
| Thermal Conductivity (at 25°C) | 16.3 W/(m·K) | — |
| Thermal Conductivity (at 100°C) | 21.5 W/(m·K) | — |
| Thermal Conductivity (at 200°C) | 25.2 W/(m·K) | — |
| Linear Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ /K | — |
| Density | 7.93 g/cm³ | — |
| Operating Temperature Range | −196°C to +870°C | — |
| Cold Work Formability | Excellent (continuous coil drawing) | — |
Corrosion Resistance Characteristics
The austenitic stainless steel composition provides superior resistance to:
- Atmospheric Corrosion — Resistance to oxidation and rust formation in ambient conditions
- Acid Corrosion — Resistance to dilute sulfuric acid, phosphoric acid, and organic acids
- Chloride-Induced Pitting — Moderate resistance to pitting corrosion in chloride-containing environments
- Intergranular Corrosion — Resistance to sensitization when properly heat-treated (solution annealed)
- Stress Corrosion Cracking (SCC) — Improved SCC resistance compared to lower-alloy grades, particularly relevant in frozen-thaw cycling scenarios
Specifications
Dimensional Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4"), 25.40 mm (1") | ± 0.05 mm |
| Wall Thickness | 0.50 mm, 0.80 mm, 1.00 mm, 1.20 mm, 1.50 mm | ± 10% |
| Inner Diameter (ID) | Calculated based on OD and wall thickness | ± 0.05 mm |
| Coil Inner Diameter (Coil ID) | 100 mm – 500 mm (customizable) | ± 5 mm |
| Coil Outer Diameter (Coil OD) | Up to 1,200 mm | ± 10 mm |
| Tube Straightness | ≤ 1.5 mm/m | — |
| Surface Roughness (Ra) | ≤ 0.8 μm (interior), ≤ 1.6 μm (exterior) | — |
| End Condition | Plain cut, beveled, or crimped (as specified) | — |
Manufacturing Standards & Compliance
| Standard | Applicability |
|---|---|
| ASTM A269 / A269M | Welded austenitic stainless steel tubing |
| ASTM B462 / B462M | Welded austenitic stainless steel tubing (general) | ASTM A778 / A778M | Welded austenitic stainless steel tubing (cold-drawn) |
| EN 10216-5 | Austenitic stainless steel tubing (European) |
| GB/T 12771 | Stainless steel seamless and welded tubing (Chinese National Standard) |
| GB/T 14976 | Seamless stainless steel tubing for pressure applications |
Manufacturing Process
Process Flow Overview
- Raw Material Selection & Inspection — Incoming stainless steel strip or coil is inspected for chemical composition (via Optical Emission Spectrometry, OES), surface quality, and dimensional accuracy. Mill test certificates (Mill Test Reports, MTRs) are verified against specified grade requirements.
- Coil Forming & Welding — Cold-rolled stainless steel strip is precisely formed into a tubular configuration. The longitudinal seam is welded using Advanced Autogenous TIG (Tungsten Inert Gas) welding, ensuring a clean, high-integrity weld joint free of filler metal contamination. Weld parameters are controlled to minimize heat-affected zone (HAZ) distortion.
- Weld Annealing (Solution Heat Treatment) — The welded tube coil undergoes solution annealing at temperatures between 1050°C and 1150°C, followed by rapid quenching. This process dissolves carbide precipitates at the weld and grain boundaries, restoring full austenitic microstructure and maximizing corrosion resistance.
- Cold Drawing & Sizing — The annealed tube is cold-drawn through precision tungsten carbide (WC) dies to achieve exact final outer diameter and wall thickness dimensions. Cold working introduces beneficial work hardening, improving yield strength while maintaining ductility.
- Pickling & Passivation — The drawn tube is subjected to acid pickling (typically using a citric acid or dilute nitric/hydrofluoric acid solution) to remove surface scale and discoloration. Subsequent passivation treatment forms a stable, protective chromium oxide (Cr₂O₃) passive film on the surface.
- Surface Cleaning & Polishing — Interior and exterior surfaces are cleaned using ultrasonic methods or mechanical brushing to achieve the specified surface roughness values. Electropolishing is available as an optional finish for critical applications requiring ultra-smooth internal surfaces.
- Coiling & Packaging — The finished tube is coiled into the specified coil configuration using automated coiling equipment. Each coil is wrapped in protective film, placed in moisture-proof packaging, and secured for transport. Each coil is tagged with a unique identification label referencing the batch number, material grade, and heat treatment lot.
- Final Quality Inspection — Comprehensive final inspection includes dimensional verification (OD, wall thickness, straightness), surface quality assessment, hydrostatic pressure testing, and spectroscopic analysis for material verification.
Anti-Freeze Design Considerations in Manufacturing
Informed by research on fresh air unit coil freezing mechanisms, the manufacturing process incorporates specific design and quality control measures to address freeze-related failure modes:
- Wall Thickness Uniformity Control — Tighter tolerance control on wall thickness (± 10%) ensures consistent hydraulic resistance and thermal performance, reducing the risk of localized flow stagnation that can precipitate ice formation.
- Enhanced Hydrostatic Testing — All coils undergo hydrostatic pressure testing at 1.5× the maximum working pressure (MWP) to verify weld integrity and structural soundness under conditions that simulate freeze-induced hydraulic expansion forces.
- Material Selection for Low-Temperature Performance — The austenitic stainless steel grade maintains ductility and toughness at cryogenic temperatures (down to −196°C), preventing brittle fracture during freeze-thaw cycling.
- Surface Quality for Flow Efficiency — Low surface roughness specifications minimize flow resistance, promoting uniform fluid distribution through the coil and reducing stagnation zones where ice nucleation is most likely to occur.
Applications
Primary Application Domains
- Fresh Air Units (FAUs) — Heat exchanger coils for air handling units providing conditioned fresh air in commercial buildings, hospitals, laboratories, and clean rooms. The coil tubes serve as the heat transfer medium for both heating and cooling circuits.
- HVAC Heat Exchangers — Evaporator and condenser coils for rooftop units (RTUs), packaged terminal air conditioners (PTACs), chiller systems, and heat pump systems.
- Industrial Process Cooling — Coil assemblies for industrial process chillers, refrigeration systems, and thermal management in manufacturing facilities.
- Food & Beverage Industry — Heat exchanger coils for pasteurization systems, beverage cooling, ice-making equipment, and food processing thermal management (FDA-compliant grades available).
- Marine & Offshore Applications — Heat exchanger coils for marine HVAC systems, ballast water treatment systems, and offshore platform thermal management (marine-grade 316L available upon request).
- Pharmaceutical & Biotechnology — Clean-in-place (CIP) compatible coil assemblies for pharmaceutical manufacturing, bioreactor thermal control, and ultra-pure water (UPW) systems.
- Cold Storage & Refrigeration — Evaporator coils for cold storage warehouses, blast freezers, and refrigerated transportation systems, where freeze protection and low-temperature performance are critical.
Critical Performance in Freeze-Prone Environments
The Stainless Steel Coil Tube is particularly suited for applications where freeze risk is elevated, including:
- Unheated or poorly insulated air handling units in cold climates
- Direct expansion (DX) evaporator coils exposed to high humidity and low ambient temperatures
- Heat recovery wheels and plate heat exchangers operating near the dew point
- Outdoor unit installations in regions with sub-zero winter temperatures
Quality Certifications & Compliance
Product Certifications
| Certification | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering manufacturing, quality control, and continuous improvement processes |
| ISO 14001:2015 | Environmental Management System certification demonstrating commitment to environmentally responsible manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System certification |
| EN 10204 3.1 | Third-party inspection certificate for material and product conformity |
| CE Marking | Conformity with European directives for product safety and compliance |
| NACE MR0175 (Available) | Oil and gas industry material certification ( |