Stainless Steel Coil Tube (Coiltube) — HVAC-Grade Seamless Tubing
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Reference No.: 1344
Category: Precision Coil Tubing for Central Air Conditioning Fan Coil Units (FCU)
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-formed, continuous-length stainless steel tubing engineered specifically for integration into central air conditioning fan coil units (Fan Coil Units, FCU) and related hydronic heat exchange systems. Unlike conventional straight-length tubing, the Coiltube is manufactured in a pre-coiled configuration, enabling direct installation into evaporator and condenser assemblies without the need for on-site bending or forming operations. This product line leverages the superior corrosion resistance, thermal conductivity, and mechanical integrity of austenitic stainless steel to deliver long-service-life performance in demanding HVAC (Heating, Ventilation, and Air Conditioning) environments.
The Coiltube is designed to serve as the primary fluid-carrying element within fan coil unit heat exchangers, where it interfaces with refrigerant or water circuits. Its coil geometry maximizes surface area within a compact footprint, facilitating efficient heat transfer between the circulating fluid and the ambient air stream. The product is particularly suited for applications requiring hygienic fluid handling, resistance to microbial growth, and compliance with indoor air quality standards.
Material & Properties
Base Material
The Coiltube is fabricated from high-purity austenitic stainless steel, conforming to recognized international standards. The primary grade options include:
- SAE 304 (UNS S30400): General-purpose grade offering excellent corrosion resistance in non-aggressive environments. Chromium (Cr) content of 18–20% with Nickel (Ni) content of 8–10.5%.
- SAE 316 (UNS S31600): Enhanced grade with Molybdenum (Mo) addition (2–3%) providing superior resistance to pitting and crevice corrosion, particularly in chloride-rich or humid indoor air environments.
- SAE 316L (UNS S31603): Low-carbon variant of 316 (Carbon ≤ 0.03%) recommended for welded assemblies to minimize sensitization and intergranular corrosion risks.
Mechanical Properties (Typical, Annealed Condition)
| Property | SAE 304 | SAE 316 / 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75 ksi) | ≥ 485 MPa (70 ksi) | ASTM A213 / A269 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (30 ksi) | ≥ 170 MPa (25 ksi) | ASTM A213 / A269 |
| Elongation (% at Break) | ≥ 40% | ≥ 35% | ASTM A213 / A269 |
| Hardness (HRB, Max) | ≤ 95 | ≤ 95 | ASTM A955 |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | ASTM E153 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /K | 16.8 × 10⁻⁶ /K | ASTM E228 |
Corrosion Resistance Characteristics
- Resistance to atmospheric corrosion in indoor environments: Excellent (Passivation layer stable at pH 4–10)
- Pitting Resistance Equivalent Number (PREN): SAE 304 — 19; SAE 316 — 24–26; SAE 316L — 24–26
- Resistance to deionized water and treated cooling water circuits: Excellent
- Resistance to common HVAC sanitizing agents (quaternary ammonium compounds, hydrogen peroxide-based): Good (316/316L preferred for aggressive formulations)
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 9.52 mm (3/8") to 25.4 mm (1") — standard; custom upon request | ASTM A269 |
| Wall Thickness (WT) | 0.5 mm to 1.5 mm (0.020" to 0.059") | ASTM A213 |
| Coil Inner Diameter (CID) | 300 mm to 600 mm (12" to 24") — configurable per application | Manufacturer Specification |
| Tubing Length per Coil | 15 m to 100 m (50 ft to 330 ft) per continuous coil | Manufacturer Specification |
| Surface Finish | Bright Annealed (BA) / Pickled & Passivated (P&P); Ra ≤ 0.4 μm | ASTM A478 |
| Tolerance — OD | ±0.05 mm (±0.002") | ASTM A269 |
| Tolerance — Wall Thickness | ±10% of nominal | ASTM A213 |
| End Condition | Plain, beveled, or crimped (per customer requirement) | Manufacturer Specification |
| Operating Temperature Range | −40°C to +250°C (−40°F to +482°F) | ASME BPV Code |
| Maximum Working Pressure | 1.6 MPa (232 psi) at 25°C (typical, OD 9.52 mm, WT 0.8 mm) | ASME BPV VIII |
| Hydrostatic Test Pressure | 1.5 × Maximum Working Pressure | ASTM A213 |
| Coil Winding Tension | Controlled to prevent permanent deformation; residual stress < 30% of yield | Internal QC Protocol |
Manufacturing Process
The production of the Stainless Steel Coiltube follows a rigorous multi-stage process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: High-purity stainless steel wire rod or strip is procured from certified mill suppliers, with full traceability to heat number. Incoming material undergoes spectrographic analysis (Optical Emission Spectrometry, OES) to verify chemical composition compliance with ASTM A240 / JIS G4305.
- Coil Forming (Cold Bending): Straight stainless steel tubing (pre-manufactured via seamless piercing or cold-drawn extrusion) is fed through a precision bending machine equipped with CNC-controlled guides and tensioners. The tube is incrementally wound into the target coil diameter with controlled bending radii (minimum bend radius ≥ 3× OD) to prevent wall thinning, ovalization, or kinking. Tension is actively managed to ensure uniform coil geometry and prevent inter-coil contact damage.
- Stress Relief Annealing (Optional): For applications requiring reduced residual stress, the coiled tube may undergo a low-temperature stress relief anneal at 400–500°C in a protective atmosphere (nitrogen or vacuum) to eliminate work-hardening effects introduced during the coiling operation.
- Pickling & Passivation: The coiled tubing is subjected to an acid pickling bath (typically a mixed HNO₃/HF solution) to remove mill scale, discoloration, and surface contaminants. This is followed by a nitric acid passivation step to establish a chromium-rich passive oxide film (Cr₂O₃) on the surface, enhancing corrosion resistance. Post-passivation, the tube is rinsed with deionized water and dried.
- End Preparation: Coil ends are cut to length and prepared per customer specification — options include plain cut ends, chamfered/beveled ends for brazing or welding, or crimped ends for mechanical fitting connections.
- Quality Inspection: Each coil undergoes 100% dimensional inspection (OD, WT, coil diameter, length), visual surface examination, and hydrostatic pressure testing. Sample lots are subjected to eddy current testing (per ASTM E709) to detect internal and external surface defects. Chemical composition is verified via XRF (X-ray Fluorescence) or OES analysis.
- Packaging & Dispatch: Coils are wrapped in protective film, secured with strapping, and packed in wooden crates or export-grade cartons with desiccant to prevent moisture ingress during transit.
Applications
The Stainless Steel Coiltube finds primary application in the following domains:
- Central Air Conditioning Fan Coil Units (FCU): Serves as the refrigerant or water-carrying tube in evaporator and condenser heat exchangers of commercial and residential FCU systems. The coil configuration allows direct integration into fin-tube heat exchanger assemblies, reducing manufacturing time and improving thermal performance.
- VRF (Variable Refrigerant Flow) Systems: Used in multi-split and VRF indoor unit heat exchangers where compact coil geometry and high-efficiency heat transfer are critical.
- Chilled Water Circulation Systems: Employed in terminal unit piping and heat recovery coils for energy-efficient HVAC systems.
- Medical and Pharmaceutical HVAC: In facilities requiring hygienic fluid handling and resistance to microbial contamination, the passivated stainless steel surface inhibits biofilm formation, supporting compliance with GMP (Good Manufacturing Practice) and ISO 14644 cleanroom standards.
- Food Processing and Beverage Cooling: Suitable for refrigeration coils in food-grade environments where contact with food-safe fluids is required.
- Marine HVAC Systems: SAE 316/316L grades provide resistance to salt-laden atmospheric conditions in shipboard air conditioning applications.
Quality Certifications & Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — manufacturing process control and continuous improvement |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing practices |
| ASTM A213 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High Temperature Service |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and General Lines at High Temperatures |
| ASME BPV Code (Section VIII) | Pressure vessel and piping component qualification for mechanical design and pressure testing |
| JIS G4305 | Japanese Industrial Standard for Stainless Steel Tubes for General Use |
| EN 10216-5 | European Standard for Technical Delivery Conditions for Welded Stainless Steel Tubes for General Purposes |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects (applicable for potable water and food-grade applications) |
| RoHS 2.0 / REACH | Restriction of Hazardous Substances and Registration, Evaluation, Authorisation and Restriction of Chemicals compliance |
Unique Selling Points
- Pre-Coiled Configuration: Eliminates on-site bending operations, reducing installation time by up to 40% and minimizing the risk of bending-induced defects (kinking, wall thinning) that can compromise heat exchanger performance and leak integrity.
- Enhanced Hygienic Performance: The passivated austenitic stainless steel surface provides a smooth, non-porous finish (Ra ≤ 0.4 μm) that resists biofilm adhesion — a critical advantage over copper and carbon steel alternatives in HVAC applications where indoor air quality (IAQ) is paramount.
- Superior Corrosion Resistance: In humid indoor environments with exposure to sanitizing agents and condensate, the Coiltube exhibits negligible corrosion rates compared to traditional materials, extending service life beyond 20 years under normal operating conditions.
- Thermal Efficiency: The precise coil geometry ensures uniform fin spacing and optimal air-side heat transfer coefficients, contributing to higher COP (Coefficient of Performance) in FCU systems.
- Full Trace