Stainless Steel Coil Tube for HVAC Fan Coil Applications
Product Code: 1444 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Overview
The Stainless Steel Coil Tube (SSCT) is a precision-engineered continuous coil of seamless or welded stainless steel tubing, specifically designed for use in column-mounted fan coil units (FCUs) within vertical air conditioning systems. This product represents a critical heat exchange component in modern hydronic HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, delivering superior thermal performance, corrosion resistance, and long-term operational reliability in demanding commercial and industrial environments.
Unlike conventional carbon steel or copper coil tubes, the SSCT offers an exceptional balance of mechanical strength, hygienic surface finish, and resistance to both external environmental degradation and internal fluid-induced corrosion. The coil configuration allows for compact, high-surface-area heat exchanger designs that maximize heat transfer efficiency within the spatial constraints of vertical fan coil unit enclosures.
Material Composition & Physical Properties
The coil tube is manufactured from premium-grade austenitic stainless steel, selected for its outstanding combination of thermal conductivity, corrosion resistance, and formability. The following table summarizes the key material specifications:
| Property | Specification | Standard Reference |
|---|---|---|
| Base Material Grade | ASTM A269 / A270 Grade 304 (UNS S30400) or Grade 316 (UNS S31600) | ASTM International |
| Chemical Composition (304) | C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Cr 18.0–20.0%, Ni 8.0–10.5%, Fe Balance | ASTM A269 |
| Chemical Composition (316) | C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, Fe Balance | ASTM A269 |
| Tensile Strength | ≥ 515 MPa (74,700 psi) | ASTM A269 |
| Yield Strength (0.2% offset) | ≥ 205 MPa (29,700 psi) | ASTM A269 |
| Elongation (minimum) | ≥ 40% in 2 inches | ASTM A269 |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) (304); 14.6 W/(m·K) (316) | ASM Handbook |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C (304); 16.6 × 10⁻⁶ /°C (316) | ASM Handbook |
| Density | 8.00 g/cm³ (304); 8.03 g/cm³ (316) | ASM Handbook |
| Surface Finish | No. 1 Annealed (pickled) or No. 4 Brushed; optional electropolished | ASTM A478 / A479 |
| Maximum Operating Temperature | 870°C (1,598°F) in air; 425°C (797°F) in aqueous service | ASM Handbook |
| Minimum Operating Temperature | Cryogenic to −196°C (−321°F) with no loss of toughness | ASTM A269 |
Dimensional Specifications
The coil tube is available in a range of outer diameters (OD), wall thicknesses (WT), and coil configurations tailored to specific fan coil unit design requirements. Standard dimensional ranges are presented below:
| Parameter | Range / Options | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (¼") – 19.05 mm (¾") | ±0.15 mm (±0.006") |
| Wall Thickness (WT) | 0.50 mm – 1.50 mm (0.020" – 0.059") | ±10% of nominal |
| Coil Diameter (CD) | 150 mm – 600 mm (6" – 24") | ±5 mm (±0.20") |
| Coil Length per Spool | 10 m – 500 m (33 ft – 1,640 ft) | As ordered |
| Bend Radius (minimum) | 2.5× OD | — |
| Coil Pitch (spacing between turns) | 2.0 mm – 6.0 mm (adjustable) | ±0.5 mm |
| End Condition | Plain cut, notched, or flared per specification | — |
Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous, multi-stage manufacturing workflow adhering to international quality management standards:
- Raw Material Sourcing & Inspection: Hot-rolled stainless steel strip or round bar is procured from certified mills (e.g., Outokumpu, POSCO, or domestic equivalent). Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition and mechanical property testing to ensure compliance with ASTM A269/A270 specifications.
- Forming & Welding (for welded tube): The strip is fed through a roll-forming line where precision rollers shape it into a circular cross-section. A high-frequency induction welding (HFW) process is then applied, producing a fully fused longitudinal seam. The weld zone is subsequently ground and polished to eliminate surface discontinuities.
- Seamless Tube Production (for seamless variant): Austenitic stainless steel billets are heated to 1,100–1,200°C and pierced on a Mannesmann-type piercing mill to produce hollow tubes. Successive hot-rolling and cold-drawing operations reduce the tube to final dimensions while maintaining metallurgical integrity.
- Pipe Bending & Coiling: The straight tube sections are fed into a CNC-controlled pipe bending machine. The bending process employs a combination of mandrel support, wiper dies, and clamp dies to achieve precise coil geometry with minimum ovality distortion (≤ 2% of OD). The bend radius is carefully controlled to prevent wall thinning or wrinkling, particularly in thin-wall configurations.
- Heat Treatment & Annealing: Post-forming annealing is conducted at 1,010–1,120°C followed by rapid water quenching to restore full austenitic microstructure, relieve residual stresses, and achieve maximum ductility and corrosion resistance. The solution-treated tube is then pickled and passivated to remove surface scale and form a protective chromium oxide film.
- Surface Finishing: Depending on application requirements, the coil tube may undergo additional surface treatments including mechanical polishing (No. 4 finish, Ra ≤ 0.8 μm), electropolishing (Ra ≤ 0.4 μm), or chemical passivation using nitric acid or citric acid solutions to enhance passive layer stability.
- Quality Control & Testing: Each production lot is subjected to comprehensive inspection including dimensional verification (OD, WT, coil diameter), hydrostatic pressure testing (at 3–5× design pressure), dye penetrant testing (DPT) of weld seams, and visual inspection. Samples are retained for spectrographic re-analysis and mechanical property verification.
- Packaging & Dispatch: Completed coil tubes are wrapped in protective polyethylene film, secured on wooden or steel spools, and labeled with material certificates (MTC), heat numbers, and dimensional data prior to shipment.
Applications
The Stainless Steel Coil Tube is engineered for deployment in a wide spectrum of HVAC and fluid handling applications, with particular emphasis on the following domains:
- Column-Mounted Fan Coil Units (FCUs) in Vertical Air Conditioning Systems: The primary application domain. The coil tube serves as the hydronic heat exchanger core within vertical FCUs installed in commercial office buildings, hospitals, laboratories, and hospitality facilities. The stainless steel construction ensures long-term resistance to corrosion from treated water, glycol-based antifreeze solutions, and humid ambient conditions.
- Commercial & Institutional HVAC Systems: Used in chillers, boilers, and heating/cooling distribution loops where the tube functions as a secondary-side heat exchanger element. The material's compatibility with potable water systems makes it suitable for direct-contact applications.
- Food & Beverage Processing: The hygienic surface finish (electropolished, Ra ≤ 0.4 μm) and compliance with FDA 21 CFR requirements render the SSCT ideal for heat exchangers in pasteurization, sterilization, and CIP (Clean-in-Place) systems.
- Pharmaceutical & Biotechnology: GMP (Good Manufacturing Practice) compliant coil tubes are employed in cleanroom HVAC systems, process water loops, and steam sterilization circuits where material purity and corrosion resistance are critical.
- Marine & Offshore HVAC: Grade 316 coil tubes with molybdenum-enhanced pitting resistance are specified for HVAC systems on naval vessels, offshore platforms, and coastal installations exposed to saltwater-laden atmospheres.
- Industrial Process Cooling & Heating: The SSCT is integrated into custom heat exchanger assemblies for chemical processing, semiconductor fabrication, and data center cooling systems where aggressive process fluids or high-purity requirements preclude the use of carbon steel or copper.
- Domestic & Residential HVAC: In premium residential applications, stainless steel coil tubes are used in high-efficiency condensing boilers and radiant floor heating systems, offering extended service life compared to copper alternatives.
Unique Selling Points
- Exceptional Corrosion Resistance: The austenitic stainless steel matrix provides inherent resistance to general corrosion, pitting, crevice corrosion, and intergranular corrosion—significantly outperforming carbon steel and even copper in chloride-containing or chemically aggressive environments.
- Hygienic & Food-Grade Compliance: Available with electropolished surfaces meeting FDA 21 CFR 184.1860, EU 1935/2004, and 3-A Sanitary Standards, making the SSCT suitable for the most demanding sanitary applications without risk of microbial contamination or material leaching.
- Design Flexibility: The coil tube can be custom-configured in terms of OD, wall thickness, coil diameter, and pitch to match specific heat exchanger design requirements, enabling optimized thermal performance and compact integration within vertical FCU enclosures.
- Long Service Life & Low Maintenance: With proper installation and maintenance, the SSCT offers a service life exceeding 25–30 years in hydronic HVAC applications, substantially reducing lifecycle costs compared to carbon steel alternatives that require frequent replacement due to corrosion.
- Thermal Cycling Resilience: The austenitic microstructure maintains ductility and fatigue resistance through repeated thermal cycling, preventing crack initiation and propagation in systems subject to frequent start-stop operation.
- Environmental Sustainability: Stainless steel is 100% recyclable with no degradation of material properties, supporting circular economy objectives and reducing the environmental footprint of HVAC infrastructure over its full lifecycle.
Quality Certifications & Compliance
The Stainless Steel Coil Tube is manufactured and tested in accordance with the following international standards and certifications:
| Standard / Certification | Scope | Authority |
|---|---|---|
| ASTM A269 | Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Tubes for Chemical and Heat-Exchanging Equipment | ASTM International |
| ASTM A270 | Specification for Seamless and Welded Austenitic Stainless Steel Tubes for General Applications | ASTM International |
| EN 10216-5 | Non-ferrous metallic tubes and their fittings for pressure purposes — Technical delivery conditions — Part 5: Seamless austenitic stainless steel tubes | CEN |
| ISO 9001:2015 | Quality Management Systems — Requirements | ISO |
| ISO 14001:2015 | Environmental Management Systems — Requirements | ISO |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for pressure-containing applications | European Union |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects (where applicable) | NSF International |
| Material Test Certificate (MTC) | EN 10204 Type 3.1 — Full material certification with heat number traceability | EN 10204 |
| TÜV / SGS Inspection | Third-party verification of manufacturing process and product conformity | TÜV Rheinland / SGS |
Technical Notes & Installation Guidelines
Note: When integrating the Stainless Steel Coil Tube into fan coil unit heat exchangers, it is critical to maintain material compatibility throughout the hydronic circuit. Avoid direct electrical contact between stainless steel components and dissimilar metals (e.g., carbon steel, aluminum) to prevent galvanic corrosion. If mixed-metal assemblies are unavoidable, use insulating gaskets or apply conformal coatings at junction points. Additionally, ensure that the water treatment program includes appropriate inhibitors (e.g., silicates, molybdates) to protect the passive chromium oxide layer and prevent chloride-induced pitting in Grade 304 applications. For chloride-rich environments exceeding 200 ppm Cl⁻, Grade 316 or duplex stainless steel (e.g., UNS S32205) is recommended.
Wenzhou Jixing Metal Materials Co., Ltd. maintains full traceability from raw material heat number through final product dispatch, ensuring complete supply chain accountability and enabling end-users to verify material provenance and compliance documentation for regulatory and warranty purposes.