Stainless Steel Coil Tube — HVAC & Fan Coil Unit Application Series

Product Overview

Wenzhou Jixing Metal Materials Co., Ltd (温州吉兴金属材料有限公司) manufactures precision-engineered stainless steel coil tubes designed for integration into fan coil units (FCU), air conditioning systems, and hydronic heating and cooling installations. These coil tubes serve as the core heat exchange elements within terminal air distribution equipment, facilitating efficient thermal transfer between circulating refrigerant or hot water and ambient air drawn through the unit.

The product designation Coil Tube (盘管) encompasses both primary refrigerant coil tubes and secondary water-side coil tubes, fabricated to meet the stringent dimensional tolerances, surface quality requirements, and corrosion resistance standards demanded by the HVAC (Heating, Ventilation, and Air Conditioning) industry.

Material & Properties

Coil tubes are manufactured from austenitic stainless steel grades selected for their superior corrosion resistance, thermal conductivity, and mechanical formability:

Key mechanical and physical properties for Grade 304 coil tube stock (annealed condition):

Specifications

Parameter Specification / Range Standard Reference
Outer Diameter (OD) 6.0 mm – 25.4 mm (typical: 9.52 mm / 3/8", 12.7 mm / 1/2", 15.88 mm / 5/8") ASTM A213 / GB/T 12771
Wall Thickness 0.5 mm – 2.0 mm ASTM A213 / EN 10216-5
Coil Length (per roll) 3 m – 50 m (customizable) —
Coil Inner Diameter (ID) 150 mm – 600 mm —
Surface Finish No. 4 Brushed / 2B Annealed / Polished (Ra ≤ 0.4 μm) ASTM A480
Dimensional Tolerance (OD) ±0.05 mm – ±0.15 mm ISO 1128 / GB/T 6393
Dimensional Tolerance (Wall) ±0.03 mm – ±0.10 mm ISO 1128 / GB/T 6393
Seam Type Welded (TIG / Argon Shielded) or Seamless ASTM A213 / EN 10216-5
Bend Radius (minimum) ≥ 3 × OD (without mandrel); ≥ 2 × OD (with mandrel) —
Fin Spacing (if finned) 2.0 mm – 4.5 mm (flat plate or spiral wound fins) ASHRAE 15
Hydrostatic Test Pressure 1.5 × working pressure, minimum 2.0 MPa ASTM A213 / ASME B31.5
Working Pressure Up to 2.5 MPa (standard); 4.0 MPa (reinforced) EN 12828
Operating Temperature Range −40°C to +250°C —
Refrigerant Compatibility R-410A, R-32, R-134a, R-22, HFO blends ASHRAE 34

Manufacturing Process

The production of stainless steel coil tubes for HVAC applications follows a rigorous multi-stage manufacturing workflow:

  1. Raw Material Selection and Incoming Inspection: Cold-rolled stainless steel strip (coil) is sourced from certified mills and subjected to spectrographic analysis (PMI — Positive Material Identification) to verify chemical composition compliance with ASTM A240 / GB/T 4237 specifications.
  2. Forming and Welding: The strip is formed into a tubular profile using precision roll-forming dies. For welded tubes, the seam is closed using Tungsten Inert Gas (TIG) welding with high-purity argon (99.999%) shielding to prevent oxidation. For seamless tubes, piercing or extrusion methods are employed.
  3. Heat Treatment (Solution Annealing): Welded tubes undergo solution annealing at 1050–1150°C followed by rapid quenching to dissolve carbide precipitates, restore full austenitic microstructure, and ensure maximum corrosion resistance.
  4. Pickling and Passivation: Tubes are immersed in a mixed acid bath (HNO₃/HF) to remove heat scale and mill scale, followed by nitric acid passivation to establish a stable chromium oxide protective film on the surface.
  5. Coiling and Coiling Winding: The straightened tube is coiled to the required length and diameter using CNC-controlled coiling machines with precision tension control to prevent tube deformation or ovality.
  6. Fin Application (for finned coil assemblies): Aluminum or stainless steel fins are applied via slip-fit, brazed, or mechanically pressed methods to maximize heat transfer surface area.
  7. Quality Inspection: Each coil undergoes dimensional verification (OD, wall thickness, straightness), hydrostatic pressure testing, visual inspection of weld seams, and surface finish assessment.
  8. Packaging: Finished coils are wrapped in protective film, placed on wooden pallets or steel frames, and labeled with material certification documents (Mill Test Certificates — MTCs).

Applications

Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd are designed for a broad spectrum of HVAC and thermal management applications:

Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management systems and certifications ensuring product conformity with international standards:

Unique Selling Points

1. Precision Dimensional Control: Advanced CNC coiling technology ensures uniform coil diameter, consistent tube straightness, and minimal ovality (≤ 0.5% of OD), enabling seamless integration into automated coil assembly lines.

2. Superior Surface Integrity: Full passivation treatment guarantees a stable passive film (Cr₂O₃) thickness of ≥ 5 nm, providing long-term corrosion protection and eliminating the need for additional surface treatment at the assembly stage.

3. Customizable Configuration: Flexible manufacturing capability supports custom OD, wall thickness, coil length, and coil diameter configurations to match specific OEM coil assembly designs and heat exchanger geometries.

4. Comprehensive Traceability: Each production batch is accompanied by full chemical analysis (PMI verified), mechanical property test results, and hydrostatic test documentation, ensuring complete material traceability from mill to installation.

5. Industry-Specific Expertise: Deep understanding of HVAC coil assembly requirements — including bend radius optimization, fin compatibility, and refrigerant/water flow dynamics — enables technically informed product recommendations tailored to end-use applications.

Terminology Reference

In alignment with the industry-standard terminology framework defined in "盘管、盘管与风机空调采暖装置 一般名词术语题录" (Glossary of General Terms and Definitions for Coil Tubes and Fan Coil Air Conditioning and Heating Devices), key terms used in this specification include: