Stainless Steel Coil Tube — Two-Pipe Fan Coil System Grade
Product Overview
The Stainless Steel Coil Tube (Product No. 743) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coil tube specifically designed for two-pipe fan coil unit (FCU) applications in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems. This product represents a high-performance solution for hydronic heat exchange, offering superior thermal conductivity, corrosion resistance, and mechanical durability compared to conventional carbon steel or copper coil alternatives.
As a fundamental component in two-pipe fan coil systems, this coil tube facilitates efficient heat transfer between the circulating water medium and the ambient air stream, enabling precise temperature regulation in controlled environments. The coil tube is formed into compact serpentine or spiral geometries that maximize surface area within constrained installation footprints, a critical requirement for modern architectural HVAC design.
Material & Properties
The coil tube is fabricated from austenitic stainless steel, primarily utilizing grades conforming to international metallurgical standards. The material selection ensures long-term operational reliability under aggressive environmental and chemical conditions.
- Primary Alloy Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 316L (UNS S31603)
- Chromium (Cr) Content: 18.0%–20.0% — provides exceptional oxidation resistance and passive film stability
- Nickel (Ni) Content: 8.0%–12.0% — ensures austenitic phase stability and ductility
- Molybdenum (Mo) Content: 2.0%–3.0% (in 316/316L grades) — enhances resistance to pitting and crevice corrosion
- Carbon (C) Content: ≤ 0.08% (304 grade); ≤ 0.03% (316L grade) — minimizes intergranular sensitization risk
- Density: 7.93 g/cm³
- Thermal Conductivity (at 20°C): 14.5–16.3 W/(m·K)
- Thermal Expansion Coefficient: 16.0–17.3 × 10⁻⁶ /K
- Yield Strength (Annealed): ≥ 205 MPa (304); ≥ 170 MPa (316L)
- Tensile Strength: ≥ 515 MPa (304); ≥ 485 MPa (316L)
- Operating Temperature Range: −196°C to +870°C (304); −273°C to +800°C (316L)
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Type | Stainless Steel Coil Tube (盘管 / Coil Tube) | — |
| Tube Outer Diameter (OD) | Φ9.52 mm / Φ12.7 mm / Φ15.88 mm (customizable) | ASME B36.19M |
| Tube Wall Thickness | 0.50 mm / 0.65 mm / 0.80 mm / 1.00 mm | ASME B36.19M |
| Coil Diameter (Pitch) | 15 mm – 50 mm (adjustable per design) | Manufacturer specification |
| Number of Rows | 1 – 4 rows (configurable) | ASHRAE Handbook — HVAC Systems and Equipment |
| Coil Length | 300 mm – 1,500 mm (standard); custom up to 3,000 mm | — |
| Surface Finish | Ba ≤ 0.5 μm (electropolished); Ra ≤ 0.8 μm (standard mill finish) | ASTM A967 |
| Connection Type | Flared, brazed, threaded, or welded end connections | ISO 11612 |
| Working Pressure | ≤ 1.6 MPa (standard); ≤ 2.5 MPa (reinforced) | EN 12828 |
| Water Flow Rate (typical) | 0.5 – 4.0 L/min per coil unit | ASHRAE 15 / ISO 5149 |
| Heat Transfer Coefficient | ≥ 450 W/(m²·K) (air side); ≥ 3,500 W/(m²·K) (water side) | ASHRAE Fundamentals |
| Corrosion Resistance | Pitting Resistance Equivalent Number (PREN) ≥ 19 (316L) | ASTM G48 |
| Dimensional Tolerance | ±0.1 mm (OD); ±0.05 mm (wall thickness) | ISO 1128 |
| Material Certification | Mill Test Certificate (MTC) per EN 10204 Type 3.1 | EN 10204 |
Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement: Cold-rolled stainless steel strip or seamless tubing is sourced from certified mills, with full chemical composition and mechanical property verification via spectroscopic analysis (OES) and tensile testing.
- Coil Forming / Tube Bending: Precision CNC-controlled bending machines form the straight tube into the required serpentine or spiral coil geometry. Bend radii are maintained at a minimum of 3× tube OD to prevent wall thinning or ovality exceeding 5%.
- Fin Attachment (if applicable): Aluminum or stainless steel fins are mechanically attached via fin-stamping or brazing processes, with fin density typically ranging from 8–12 fins per inch (FPI) to optimize heat transfer area.
- Welding / Brazing: Header connections and tube-to-header joints are fabricated using TIG (Tungsten Inert Gas) welding or silver brazing (BCuP-6) under controlled nitrogen atmosphere to prevent internal oxidation.
- Surface Treatment: Electropolishing or chemical passivation per ASTM A967 is applied to remove surface contaminants and establish a stable chromium oxide passive layer.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× the maximum working pressure, with a hold time of no less than 30 minutes, ensuring zero leakage.
- Final Inspection: Dimensional verification, visual inspection, and (where applicable) dye penetrant testing (PT) per ASTM E165 are conducted to confirm compliance with specified tolerances and defect-free surfaces.
Applications
The Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd. is engineered for demanding hydronic heat exchange applications, particularly within two-pipe fan coil systems. Key application domains include:
- Commercial HVAC Systems: Office buildings, hotels, hospitals, and retail complexes requiring precise indoor climate control through two-pipe (hot/cold water) distribution.
- Industrial Process Cooling: Heat rejection in manufacturing facilities where corrosion resistance is critical (e.g., food processing, pharmaceutical, chemical plants).
- Marine and Offshore Environments: HVAC installations on vessels and offshore platforms where resistance to saltwater-induced pitting and crevice corrosion is paramount (316L grade recommended).
- Cleanroom and Laboratory Environments: Ultra-low particulate environments where surface finish quality directly impacts air quality standards.
- Residential High-End HVAC: Premium residential installations requiring silent, efficient, and maintenance-free coil performance over extended service lives.
- District Heating and Cooling Networks: Terminal heat exchange units connected to centralized energy distribution systems.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and holds the following certifications and compliances, ensuring product reliability and international market acceptance:
- ISO 9001:2015 — Quality Management Systems certification for consistent production quality and process control.
- ISO 14001:2015 — Environmental Management Systems, demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems.
- CE Marking — Conformity with European Health, Safety, and Environmental Protection standards (EU Directive 2014/68/EU — Pressure Equipment Directive).
- ASME B36.19M Compliance — Wrought Austenitic Stainless Steel Pipe and Tube specifications.
- EN 10216-5 — European standard for welded stainless steel tubes for heat exchangers and heat sinks.
- ASME BPV Code (Section I) — Power Boilers and Pressure Vessels compliance for pressure-containing components.
- Mill Test Certificates (MTC) — Issued per EN 10204 Type 3.1 for every production batch, documenting chemical composition, mechanical properties, and heat treatment records.
- NACE MR0175 / ISO 15156 — Compliance for resistance to sulfide stress cracking in sour service environments (where applicable).
Unique Selling Points
1. Superior Corrosion Resistance: Unlike carbon steel coils requiring protective coatings, the austenitic stainless steel construction provides inherent, long-lasting corrosion resistance without degradation, eliminating the need for periodic repainting or replacement in aggressive environments.
2. Extended Service Life: With proper installation and maintenance, the coil tube offers a service life exceeding 25–30 years, significantly outperforming copper or carbon steel alternatives in corrosive conditions.
3. Design Flexibility: Available in multiple alloy grades (304, 316, 316L), tube diameters, wall thicknesses, and coil geometries to accommodate diverse system design requirements and thermal load calculations.
4. Food-Grade and Pharmaceutical Compatibility: 316L grade coils meet sanitary requirements for direct contact with potable water and food-grade process fluids, ensuring regulatory compliance in sensitive industries.
5. Precision Manufacturing: CNC-controlled forming and welding processes ensure consistent dimensional accuracy and joint integrity, reducing field installation challenges and system leakage risks.
6. Environmental Sustainability: Stainless steel is 100% recyclable, contributing to circular economy objectives and reducing the overall carbon footprint of HVAC system life-cycle costs.
Selection Methodology — Two-Pipe Fan Coil Sizing
Proper selection of the stainless steel coil tube for two-pipe fan coil applications requires systematic thermal and hydraulic analysis. The following methodology aligns with ASHRAE Handbook — HVAC Systems and Equipment guidelines:
- Heat Load Determination: Calculate total cooling and heating loads for each served zone, accounting for sensible and latent components separately.
- Entering/Leaving Air Conditions: Define design air temperatures at coil inlet (room air) and outlet (supply air), ensuring the coil can achieve the required temperature differential (ΔT).
- Water Side Parameters: Specify supply and return water temperatures (e.g., 7°C/12°C for cooling; 45°C/40°C for heating) and allowable pressure drop.
- Air Side Parameters: Determine air flow rate (CFM or m³/h), face velocity, and allowable air-side pressure drop across the coil.
- Coil Selection: Based on the above parameters, select the appropriate tube OD, wall thickness, number of rows, fin density, and overall coil dimensions using manufacturer performance curves or computational tools.
- Verification: Confirm that the selected coil meets capacity requirements with adequate safety margin (typically 10–15%) and that condensate drainage provisions are adequate for cooling applications.
Note: All specifications are subject to modification without prior notice. For project-specific requirements, consult Wenzhou Jixing Metal Materials Co., Ltd. engineering team for detailed technical consultation and custom design support.