Stainless Steel Fan Coil Tube — Coil Pipe for HVAC Systems
1. Product Overview
The Stainless Steel Fan Coil Tube (Coil Pipe) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product designed specifically for large-scale fan coil units (FCUs) used in commercial and industrial heating, ventilation, and air conditioning (HVAC) systems. This product category, catalogued under reference number 1684, represents a high-performance solution for thermal exchange applications where corrosion resistance, thermal conductivity, and mechanical durability are paramount.
Unlike conventional carbon steel coil tubes, the stainless steel variant offers superior resistance to condensation-induced corrosion, extended service life in humid environments, and compliance with stringent hygiene standards required in pharmaceutical, food processing, and cleanroom applications. The coil geometry facilitates compact installation within fan coil unit housings while maximizing heat transfer surface area per unit volume.
2. Material & Properties
2.1 Base Alloy Grades
- AISI 304 (UNS S30408) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability. Chromium (Cr) content of 18–20% and Nickel (Ni) content of 8–10.5% provide robust passive film stability in most ambient and HVAC operating environments.
- AISI 316 (UNS S31608) — Enhanced austenitic grade with 2–3% Molybdenum (Mo) addition for superior resistance to pitting and crevice corrosion, particularly in chloride-rich or coastal environments.
- AISI 316L (UNS S31603) — Low-carbon variant of 316 (C ≤ 0.03%) offering improved weldability and resistance to intergranular corrosion following welding operations.
- AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade providing enhanced resistance to sensitization at elevated temperatures, suitable for high-temperature HVAC applications.
2.2 Mechanical Properties (Annealed Condition)
| Property | AISI 304 | AISI 316 | AISI 316L | AISI 321 |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 520 | ≥ 485 | ≥ 520 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 205 | ≥ 170 | ≥ 205 |
| Elongation (% min.) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 14.6 | 14.6 | 16.3 |
| Thermal Expansion (×10⁻⁶/K, 20–100°C) | 17.3 | 16.0 | 16.0 | 17.3 |
| Density (kg/m³) | 8.00 | 8.03 | 8.03 | 8.00 |
2.3 Surface Finish Options
- 2B Finish — Cold-rolled and annealed with a matte, slightly reflective surface; suitable for general HVAC applications.
- No. 4 Brushed Finish — Medium-grit polishing providing a uniform satin appearance with directional grain pattern.
- Mirror Polish (8K) — High-gloss reflective surface achieved through electrolytic polishing; ideal for sanitary and food-grade applications.
- Pickled & Passivated (P&P) — Chemically cleaned and passivated surface free of scale and iron contamination; enhances corrosion resistance.
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | Ø6.0 mm – Ø35.0 mm (custom sizes available) |
| Wall Thickness | 0.30 mm – 1.50 mm |
| Coil Pitch | 6 mm – 25 mm (adjustable per design requirements) |
| Coil Diameter | Ø50 mm – Ø150 mm |
| Coil Length | 1.0 m – 6.0 m (standard); up to 12.0 m (special order) |
| Coil Turns | 10 – 80 turns per assembly |
| Material Grades | AISI 304, 304L, 316, 316L, 321 |
| Operating Temperature Range | −196°C to +450°C |
| Maximum Operating Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) |
| Surface Roughness (Ra) | ≤ 0.8 µm (2B); ≤ 0.2 µm (Mirror Polish) |
| Dimensional Tolerance (OD) | ±0.05 mm |
| Dimensional Tolerance (Wall Thickness) | ±0.02 mm |
| Applicable Standards | ASTM A269, ASTM A270, EN 10217-7, GB/T 12771 |
| End Treatment | Plain cut, flared, threaded, or brazed joints |
| Packaging | Wooden crate / export-grade carton with desiccant |
4. Manufacturing Process
4.1 Process Flow Overview
- Strip Preparation — Cold-rolled stainless steel strip (coil) is unwound, levelled, and inspected for surface defects, thickness uniformity, and chemical composition via Optical Emission Spectroscopy (OES).
- Forming & Coiling — The flat strip is fed through a progressive die set or roll-forming station that imparts the helical coil geometry. Forming forces are precisely controlled to prevent strain hardening and ensure dimensional accuracy.
- Heat Treatment (Annealing) — For cold-worked coils requiring improved ductility, solution annealing is performed at 1050–1150°C in a protective atmosphere (argon or dissociated ammonia) followed by controlled cooling to restore full austenitic structure and eliminate residual stresses.
- Pickling & Passivation — The annealed coils are immersed in a mixed acid bath (HNO₃ + H₂SO₄) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide passive layer.
- Finishing — Surface finishing (brushing, polishing, or electrolytic polishing) is applied according to customer specifications.
- Quality Inspection — Comprehensive testing including dimensional measurement (OD, wall thickness, coil pitch), hydrostatic pressure testing, ultrasonic flaw detection, and chemical analysis.
- Packaging & Dispatch — Final products are individually wrapped, packed with moisture-absorbing desiccants, and secured in export-grade wooden crates.
4.2 Critical Process Parameters
- Forming Temperature: Room temperature (cold forming) for grades 304/316; pre-heating to 200–300°C may be employed for thicker wall sections to reduce forming forces.
- Reduction Ratio: Controlled at ≤ 25% per pass to minimize work hardening and maintain formability.
- Interpass Annealing: Performed when cumulative strain exceeds 20% to prevent cracking during subsequent forming operations.
- Coil Springback Compensation: Forming dies are pre-set with calculated compensation angles (typically 2°–5°) to achieve target coil geometry after elastic recovery.
5. Applications
5.1 Primary Application Domains
- Large Fan Coil Units (FCUs): The principal application domain. Stainless steel coil tubes serve as the heat exchange element in FCUs for commercial buildings, hospitals, laboratories, and industrial facilities. The coil's compact geometry and high surface-area-to-volume ratio ensure efficient heat transfer between the circulating fluid (water or refrigerant) and the airstream.
- Pharmaceutical & Biotechnology: GMP (Good Manufacturing Practice) compliant environments require coil tubes with sanitary-grade surface finishes and corrosion resistance to withstand aggressive cleaning agents (CIP — Clean-In-Place systems).
- Food & Beverage Processing: Compliance with FDA and EHEDG (European Hygienic Engineering Design Group) standards for hygienic HVAC systems in food production facilities.
- Marine & Offshore HVAC: AISI 316/316L grades provide essential resistance to salt spray and chloride-induced corrosion in marine environments.
- Semiconductor Cleanrooms: Ultra-low particulate generation and chemical inertness make stainless steel coil tubes suitable for ISO Class 1–5 cleanroom HVAC systems.
- Data Center Cooling: High-efficiency thermal management for server room environmental control systems.
5.2 Performance Advantages in Fan Coil Applications
"The selection and application of large fan coil tubes requires careful consideration of material grade, coil geometry, and operating conditions to optimize thermal performance while ensuring long-term reliability and minimal maintenance." — Adapted from industry best practices for large FCU design and selection.
- Corrosion Resistance: Eliminates the risk of condensation-induced rust and tube failure common in carbon steel alternatives, particularly in high-humidity environments.
- Hygienic Performance: Smooth internal surfaces prevent biofilm formation and facilitate effective CIP cleaning cycles.
- Thermal Stability: Maintains mechanical integrity and dimensional stability across the full HVAC operating temperature range.
- Long Service Life: Expected service life of 20–25 years under normal operating conditions, significantly exceeding carbon steel alternatives (8–12 years).
- Low Maintenance: Reduced frequency of replacement and servicing, resulting in lower total cost of ownership (TCO).
6. Quality Certifications & Compliance
6.1 Manufacturing Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to environmental stewardship.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 — Certificate Type 3.1 (Third-party inspection) available upon request.
6.2 Product Standards Compliance
| Standard | Description | Applicability |
|---|---|---|
| ASTM A269/A269M | Standard Specification for Seamless Austenitic Stainless Steel Tubing for Boilers, Heaters, and Exchangers | Material & mechanical requirements |
| ASTM A270/A270M | Standard Specification for Seamless and Wrought Austenitic Stainless Steel Tubing, Pipes, and Fittings | General tubing requirements |
| EN 10217-7 | Heat-exchange tubes, pipes and fittings — Part 7: Austenitic stainless steels | European heat exchanger applications |
| GB/T 12771 | Stainless steel seamless tubes for general purposes (Chinese National Standard) | Domestic market compliance |
| ASME B31.5 | Power Piping | Pressure system design reference |
6.3 Testing & Inspection Protocols
- Hydrostatic Pressure Testing: All coils tested at 1.5× maximum operating pressure for minimum 10 seconds with zero leakage tolerance.
- Ultrasonic Testing (UT): Non-destructive examination for internal defects, wall thickness uniformity, and seam integrity (where applicable).
- Spectrographic Analysis: Confirmed chemical composition via OES or XRF (X-ray Fluorescence) for each heat lot.
- Intergranular Corrosion Testing: ASTM A262 Practice No. 1E (Acid Solution) for grades requiring sensitization resistance verification.
- Surface Roughness Measurement: Contact profilometry per ASTM E19 for finish verification.
7. Unique Selling Points
- Precision Coil Geometry: Computer-controlled forming ensures consistent coil pitch, diameter, and turn count with tolerances of ±0.1 mm, enabling seamless integration into FCU assemblies.
- Grade Versatility: Full range of austenitic stainless steel grades available from a single supplier, simplifying procurement and ensuring material consistency across projects.
- Custom Engineering Support: Technical team available for coil geometry optimization based on specific FCU thermal load calculations and airflow requirements.
- Export-Ready Packaging: Robust packaging design ensures damage-free transit to international destinations with full traceability documentation.
- Traceability: Each coil lot is traceable to the mill heat number, enabling full supply chain traceability for quality assurance and regulatory compliance.
8. Ordering Information
When placing orders for Stainless Steel Fan Coil Tubes from Wenzhou Jixing Metal Materials Co., Ltd, customers should specify the following parameters:
- Material grade (e.g., AISI 304, AISI 316L)
- Outer diameter and wall thickness
- Coil pitch and coil diameter