Stainless Steel Coil Tube for Fan Coil Unit (FCU) Applications

Product Overview

The Stainless Steel Coil Tube (Product No. 1074) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component specifically designed for use in Fan Coil Unit (FCU) systems within Heating, Ventilation, and Air Conditioning (HVAC) installations. This coil tube serves as the primary heat exchange conduit, facilitating efficient thermal transfer between the circulating refrigerant or hot water medium and the ambient air drawn across the finned surface by the unit's axial or centrifugal fan.

A critical engineering challenge in FCU applications is the management of condensate (condensation water) formation on the coil tube outer surface when the tube temperature falls below the dew point of the surrounding air. Wenzhou Jixing Metal Materials Co., Ltd. addresses this challenge through superior surface finish control, precise dimensional tolerances, and optimized tube geometry, thereby minimizing condensation-related operational issues such as water leakage, microbial growth, and reduced thermal efficiency.

Material & Properties

Base Material Composition

Key Material Properties

Specifications

Parameter Specification Standard / Tolerance
Outer Diameter (OD) 9.52 mm, 12.7 mm, 15.88 mm, 19.05 mm ±0.10 mm (per ASTM B730)
Wall Thickness (WT) 0.50 mm, 0.80 mm, 1.00 mm, 1.20 mm ±0.05 mm
Coil Length Customized: 3 m to 50 m per coil ±2% of nominal length
Coil Inner Diameter (ID) 300 mm to 800 mm ±10 mm
Tube Roundness ≤ 10% of nominal OD ASTM A213
Surface Roughness (Ra) ≤ 0.4 μm (electropolished); ≤ 0.8 μm (mechanically polished) ASTM A967
End Condition Plain end, beveled end, or pre-flared Custom per drawing
Max Operating Pressure 2.5 MPa (at 200°C) ASME BPVC Section VIII
Hydrostatic Test Pressure 3.0 MPa (standard); up to 5.0 MPa on request 1.5× maximum working pressure
Fin Compatibility Aluminum, copper, or stainless steel fins (laser-welded or mechanically crimped) Per OEM specification
Weight (per meter) 0.32 kg/m (9.52×0.50); 1.15 kg/m (19.05×1.20) Calculated per ASTM B730

Manufacturing Process

The production of Wenzhou Jixing Metal Materials Co., Ltd. stainless steel coil tubes follows a rigorous, multi-stage manufacturing process designed to ensure dimensional precision, metallurgical integrity, and surface quality suitable for FCU condensate management requirements:

  1. Hot Rolling & Annealing: Stainless steel strip is hot-rolled to preliminary dimensions and solution-annealed at 1050–1150°C followed by rapid water quenching to achieve a fully austenitic microstructure free of carbide precipitation.
  2. Cold Rolling & Pickling: Cold rolling to target wall thickness with controlled reduction ratio (≤30% per pass) to maintain mechanical properties. Subsequent acid pickling (HNO₃/HF blend) removes scale and oxide layers.
  3. Forming & Coiling: The flat strip is formed into tube geometry via seamless or welded processes, then coiled to specified inner diameters using CNC-controlled coiling equipment with tension control to prevent deformation.
  4. Heat Treatment (Solution Annealing): Post-forming solution annealing at 1040–1120°C with controlled cooling rate (≤100°C/min) to restore full solution-strengthened condition and relieve residual stresses introduced during forming.
  5. Surface Finishing: Electropolishing or mechanical polishing to achieve Ra ≤ 0.4 μm surface finish. This ultra-smooth surface is critical for minimizing condensate film adhesion, reducing biofilm formation, and facilitating condensate drainage in FCU applications.
  6. Quality Inspection & Testing: Comprehensive inspection including visual examination, dimensional measurement (OD, WT, roundness), hydrostatic pressure testing, and non-destructive testing (NDT) including eddy current testing (ECT) and ultrasonic testing (UT) for wall thickness verification.
  7. Packaging & Protection: Protective end caps, moisture-absorbing desiccant packets, and anti-corrosion wrapping to prevent oxidation and contamination during storage and transport.

Applications

Primary Application: Fan Coil Unit (FCU) Systems

The stainless steel coil tube is the core heat exchange element in FCU systems, where it directly interfaces with both the circulating fluid medium and the conditioned air. Key application scenarios include:

Condensate Management Engineering

Based on technical analysis of condensate formation in FCU systems, the following engineering principles are applied in the design and specification of these coil tubes:

  1. Surface Hydrophobicity: The electropolished surface finish reduces the contact angle of condensate droplets, promoting faster drainage and minimizing standing water that leads to microbial proliferation
  2. Thermal Uniformity: Precise wall thickness control ensures uniform heat transfer across the tube surface, preventing localized cold spots that accelerate condensation beyond design parameters
  3. Geometric Optimization: Tube OD and WT selection is coordinated with fin spacing and pitch to optimize the balance between thermal efficiency and condensate drainage capacity
  4. Corrosion Prevention: The austenitic stainless steel matrix provides inherent resistance to condensate-induced corrosion, extending service life significantly compared to carbon steel alternatives

Quality Certifications & Standards Compliance

Product Certifications

Applicable Standards

Testing & Verification

Unique Selling Points: Wenzhou Jixing Metal Materials Co., Ltd. differentiates its stainless steel coil tube product through (1) ultra-low surface roughness (Ra ≤ 0.4 μm) specifically engineered to mitigate condensate adhesion in FCU applications, (2) full traceability from raw material heat number through final coil identification, (3) comprehensive NDT coverage ensuring zero-defect delivery, and (4) technical expertise in condensate management engineering derived from systematic study of FCU condensate formation mechanisms.