Stainless Steel Coil Tube (Coiltube) — HVAC Fan Coil Unit Application
Product No.: 1317 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous coil form of stainless steel tubing specifically designed for use in Heating, Ventilation, and Air Conditioning (HVAC) systems, with primary application in Fan Coil Units (FCUs). As a critical heat exchanger component, the coil tube facilitates efficient thermal transfer between circulating fluids (water or refrigerant) and ambient air, enabling precise temperature regulation in commercial and residential environments.
Unlike discrete tube segments, the coil tube is supplied in continuous spiral or helical form, eliminating the need for field welding or brazing at intermediate joints. This continuous configuration significantly reduces the risk of leakage points, enhances system reliability, and minimizes installation labor. The product represents an advancement over traditional copper coil tubes in terms of corrosion resistance, hygienic performance, and long-term durability, particularly in environments with high humidity or exposure to aggressive atmospheric conditions.
2. Material & Properties
2.1 Material Grades
- Grade 304 (UNS S30400 / 1.4301) — Austenitic stainless steel with excellent general corrosion resistance; the most widely specified grade for HVAC coil tubes.
- Grade 316L (UNS S31603 / 1.4404) — Low-carbon austenitic stainless steel with added molybdenum content; superior resistance to chloride-induced pitting corrosion, recommended for coastal or industrial environments.
- Grade 304L (UNS S30403 / 1.4307) — Low-carbon variant of Grade 304; enhanced resistance to intergranular corrosion during welding or heat treatment operations.
2.2 Mechanical Properties (Typical, Annealed Condition)
| Property | Grade 304 | Grade 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 480 MPa | ASTM A269 / EN 10216-5 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ASTM A269 / EN 10216-5 |
| Elongation (A50) | ≥ 40 % | ≥ 40 % | ASTM A269 |
| Hardness (HBW) | ≤ 200 | ≤ 200 | ISO 6506 |
| Impact Energy (−196 °C) | ≥ 47 J (Charpy V) | ≥ 47 J (Charpy V) | ASTM E23 |
2.3 Physical & Chemical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C (Grade 304); 14.6 W/(m·K) at 20 °C (Grade 316L)
- Specific Heat Capacity: 500 J/(kg·K) at 20 °C
- Linear Thermal Expansion Coefficient: 17.3 × 10−6 /°C (20–100 °C)
- Density: 7.93 g/cm³ (Grade 304); 8.00 g/cm³ (Grade 316L)
- Chromium (Cr): ≥ 18.0 % (Grade 304); ≥ 16.0 % (Grade 316L)
- Nickel (Ni): ≥ 8.0 % (Grade 304); ≥ 10.0 % (Grade 316L)
- Molybdenum (Mo): — (Grade 304); 2.0–3.0 % (Grade 316L)
- Carbon (C): ≤ 0.08 % (Grade 304); ≤ 0.03 % (Grade 316L)
2.4 Surface Finish
The coil tube is supplied in a 2B cold-rolled and annealed finish (Ra ≤ 0.5 μm) or electropolished finish (Ra ≤ 0.25 μm) upon request. The electropolished variant offers a superior hygienic surface, minimizing bacterial adhesion — a critical requirement in pharmaceutical and food-grade HVAC applications.
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (¼"), 9.53 mm (⅜"), 12.70 mm (½"), 15.88 mm (⅝"), 19.05 mm (¾") | ASTM A269 / EN 10216-5 |
| Wall Thickness | 0.50 mm – 1.50 mm (typical range for HVAC coil applications) | ASTM A269 |
| Tolerance on OD | ±0.10 mm | ISO 4629 |
| Tolerance on Wall Thickness | ±10 % of nominal | EN 10216-5 |
| Coil Inner Diameter (ID) | 300 mm – 600 mm (standard); up to 900 mm upon request | — |
| Coil Length (Continuous) | Up to 3000 m per coil (single continuous length) | — |
| Roundness (Ovality) | ≤ 0.1 % of OD | ISO 4629 |
| Surface Defects | No cracks, pitting, laminations, or excessive oxidation permitted | ASTM A269 |
| Heat Treatment | Solution annealing (1050–1150 °C) followed by water quench | ASTM A269 |
| Packing | Wooden crate or export-grade corrugated packaging with moisture barrier | ISO 4180 |
| Applicable Standards | ASTM A269, EN 10216-5, GB/T 12771, JIS G3459 | — |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes follows a rigorously controlled multi-stage manufacturing sequence:
- Raw Material Selection — Virgin stainless steel strip or hot-rolled coil is procured from certified mills, with full chemical composition and mechanical property verification via Spectroscopic Analysis (OES — Optical Emission Spectroscopy).
- Cold Rolling (Cold Reduction) — The strip undergoes multi-pass cold rolling to achieve the target wall thickness with tight dimensional tolerances. Inter-pass annealing may be applied to prevent work hardening.
- Seam Welding — The rolled strip is precisely joined via TIG (Tungsten Inert Gas) welding or automatic orbital welding under inert gas shielding (argon or argon-helium mixture) to ensure a defect-free, leak-tight seam with a smooth internal weld profile.
- Solution Annealing — The welded tube is subjected to solution annealing at 1050–1150 °C followed by rapid water quenching. This process dissolves carbide precipitates, restores full austenitic microstructure, and maximizes corrosion resistance and ductility.
- Pickling & Passivation — The tube surface is treated with a nitric-hydrofluoric acid pickling solution to remove scale and oxide films, followed by a passivation step to establish a protective chromium oxide layer.
- Hydrostatic Testing — Each coil is subjected to a hydrostatic pressure test at a minimum of 2.5× the maximum working pressure to verify seam integrity and detect any micro-voids or porosity.
- Coiling & Winding — The continuous tube is wound into a helical coil using a precision winding machine with controlled tension to prevent deformation, kinking, or permanent set. The coil is stabilized with steel banding and protective end caps.
- Final Quality Inspection — Incoming and outgoing quality control includes dimensional verification (caliper, micrometer), surface inspection (visual and dye penetrant testing per ASTM E709), and spectroscopic material verification.
5. Applications
5.1 Primary Application — Fan Coil Units (FCUs)
The coil tube serves as the core heat exchanger element in Fan Coil Units, which are modular HVAC terminal devices used to condition air in individual rooms or zones. In this application:
- Cooling Mode: Chilled water (typically 6–12 °C) circulates through the coil tubes while a fan draws room air across the tube bundle, extracting heat and delivering cooled air to the space.
- Heating Mode: Hot water (typically 45–70 °C) circulates through the coil tubes, transferring thermal energy to the airstream for space heating.
- Dehumidification: The cold coil surface condenses moisture from the airstream, reducing relative humidity to comfortable levels.
Stainless steel coil tubes offer a significant advantage over traditional copper alternatives in FCUs, particularly in corrosive environments (e.g., coastal regions, chemical processing facilities, and hospitals) where copper may suffer from accelerated corrosion due to interaction with condensate water containing dissolved chlorides or ammonia-based cleaning agents.
5.2 Secondary Applications
- Condensers & Evaporators in refrigeration and air conditioning systems
- Chilled Water Pipelines in commercial building HVAC distribution networks
- Heat Recovery Units (HRUs) for energy-efficient ventilation systems
- Pharmaceutical Cleanroom HVAC systems requiring hygienic-grade tubing
- Food Processing Industry HVAC and process cooling circuits
- Marine HVAC Systems where chloride resistance is paramount
- Industrial Process Heating/Cooling circuits requiring long-term reliability without maintenance downtime
6. Unique Selling Points
- Superior Corrosion Resistance — Stainless steel coil tubes exhibit exceptional resistance to atmospheric corrosion, condensate water corrosion, and chemical attack, extending service life well beyond 20 years compared to 8–12 years for copper coil tubes in aggressive environments.
- Continuous Coil Configuration — The elimination of field joints and brazing points reduces the probability of system leaks by an estimated 60–80 %, lowering lifecycle maintenance costs.
- Hygienic Surface — The electropolished finish provides a smooth, non-porous surface that inhibits biofilm formation, meeting NSF/ANSI 61 standards for potable water contact.
- Low Carbon Footprint — Stainless steel is 100% recyclable with no loss of material properties, aligning with Green Building Council (LEED/BREEAM) sustainability requirements.
- Low Maintenance — No galvanic corrosion concerns when paired with stainless steel fins, eliminating the need for periodic replacement.
- Design Flexibility — Available in a wide range of OD and wall thickness combinations to accommodate diverse design pressures and flow rates.
7. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing operations |
| ISO 14001:2015 | Environmental Management System certification |
| EN 10204 3.1 | Third-party certified material test report with full chemical and mechanical data |
| CE Marking | Compliance with European Directive 2014/68/EU (Pressure Equipment Directive) where applicable |
| NSF/ANSI 61 | Health effects testing for materials in contact with potable water |
| ASTM A269 / A270 | Standard specification for austenitic stainless steel seamless and welded tubing |
| GB/T 12771 | Chinese national standard for welded austenitic stainless steel tubes for general purposes |
| Mill Test Certificate (MTC) | Provided with every shipment, documenting material grade, heat number, and test results |
Technical Note: When specifying stainless steel coil tubes for Fan Coil Unit applications, it is critical to verify compatibility between the tube material grade and the fin material (aluminum, stainless steel, or coated steel) to prevent galvanic corrosion. In environments with chloride concentrations exceeding 500 ppm (e.g., coastal areas), Grade 316L is strongly recommended over Grade 304. For high-temperature heating applications exceeding 150 °C, additional consideration should be given to creep resistance and thermal fatigue performance of the selected grade.
Document prepared based on product knowledge reference: Wenzhou Jixing Metal Materials Co., Ltd. — Product No. 1317, Coiltube (盘管). Application context derived from: "Application and Analysis of Fan Coil Units in Air Conditioning Engineering."