Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a continuous-length tubular product manufactured in a coiled configuration, designed for seamless integration into heat exchanger assemblies, HVAC (Heating, Ventilation, and Air Conditioning) systems, and fan coil unit (FCU) applications. Produced by Wenzhou Jixing Metal Materials Co., Ltd, this coil tube is engineered to deliver superior thermal conductivity, corrosion resistance, and mechanical integrity under prolonged service conditions. The coiled form factor eliminates the need for butt-welded joints during installation, thereby reducing potential leak paths and improving overall system reliability.

This product is particularly relevant in advanced building energy management systems where intelligent control strategies—such as deep reinforcement learning (Deep RL)-based fan coil unit control methods—are employed to optimize indoor thermal comfort while minimizing energy consumption. The coil tube serves as a critical heat transfer medium within such systems, and its material and geometric consistency directly influence the thermal performance and control accuracy of the entire HVAC loop.

2. Material & Properties

2.1 Material Grades

The coil tube is available in the following austenitic stainless steel grades, conforming to international standards:

2.2 Key Physical and Mechanical Properties

Property 304 / 304L 316 / 316L 321 Unit
Density (ρ) 7.93 7.98 7.93 g/cm³
Thermal Conductivity (λ) at 100 °C 16.3 16.3 16.3 W/(m·K)
Specific Heat Capacity (cp) at 100 °C 0.50 0.50 0.50 kJ/(kg·K)
Yield Strength (σy) ≥ 205 ≥ 205 ≥ 205 MPa
Tensile Strength (σu) 515 – 720 515 – 720 515 – 720 MPa
Elongation (A) ≥ 40 ≥ 40 ≥ 40 %
Maximum Service Temperature 870 870 900 °C
Coefficient of Thermal Expansion (α) 100–200 °C 17.3 17.3 17.3 ×10⁻⁶/K

2.3 Corrosion Resistance

All specified grades exhibit a passive oxide film (Cr₂O₃) that self-heals in the presence of oxygen, providing robust protection against atmospheric corrosion, acidic environments, and common industrial chemical agents. The 316/316L grades additionally resist chloride-induced pitting corrosion, making them suitable for coastal, marine, and chemical processing environments. The 321 grade offers enhanced resistance to intergranular corrosion after exposure to sensitization temperatures, making it appropriate for high-temperature heat exchanger applications.

3. Specifications

3.1 Geometric Dimensions

Parameter Range / Value Standard Reference
Outer Diameter (OD) Φ6.0 – Φ35.0 mm ASTM A269 / ASME B36.19M
Wall Thickness (WT) 0.5 – 3.0 mm ASTM A269 / GB/T 12771
Coil Diameter (CD) Φ500 – Φ1,200 mm Manufacturer Specification
Coil Length per Spool 50 – 300 m (configurable) Manufacturer Specification
OD Tolerance ±0.10 mm ASTM A269
Wall Thickness Tolerance ±10% (min. 0.05 mm) ASTM A269
Surface Finish 2B, No. 4 Brushed, or BA (Bright Annealed) ASTM A480
End Condition Plain end, Beveled end, or Flanged Per customer requirement
Hardness (Rockwell B) ≤ 95 HRB ASTM A269

3.2 Dimensional Drawing Reference

Coil tube dimensions are defined by outer diameter (OD), wall thickness (WT), and coil winding diameter (CD). The tube is wound in a helical configuration with consistent pitch to minimize residual stress and facilitate downstream forming operations such as bending, crimping, and expansion into heat exchanger headers.

4. Manufacturing Process

4.1 Process Flow

  1. Raw Material Procurement: Hot-rolled stainless steel strip or seamless pipe stock is sourced from certified mills, with mill test certificates (MTC) verifying chemical composition and mechanical properties.
  2. Slitting and Leveling: The strip is slit to the required width and leveled to ensure flatness and dimensional accuracy prior to tube forming.
  3. Pipe Forming (ERW / Laser Welded): The leveled strip is formed into a tubular cross-section using either Electric Resistance Welding (ERW) or laser welding technology. Laser welding provides a narrower heat-affected zone (HAZ) and superior weld integrity for thin-wall applications.
  4. Heat Treatment and Pickling: The formed tube undergoes solution annealing (typically at 1050–1150 °C) followed by acid pickling to remove oxide scale and restore the passive surface layer.
  5. Precision Sizing: The tube passes through a series of sizing rolls to achieve the specified OD and WT tolerances.
  6. Coil Winding: The continuous tube is wound onto a coil reel using a controlled winding system that maintains consistent tension to prevent ovality, kinking, or springback.
  7. Surface Finishing: Optional electropolishing, passivation treatment, or protective coating is applied depending on the target application.
  8. Quality Inspection: Each coil undergoes visual inspection, dimensional measurement, hydrostatic testing, and chemical/spectrometric verification.
  9. Packaging and Shipping: Coils are wrapped in protective film, strapped, and palletized for safe transport.

4.2 Critical Process Parameters

5. Applications

5.1 HVAC and Fan Coil Units (FCU)

The primary application domain for this coil tube is in the construction of heat exchanger cores for fan coil units. In modern building automation systems, FCUs are increasingly controlled by deep reinforcement learning (Deep RL) algorithms that optimize fan speed, water valve positions, and supply temperature setpoints to achieve indoor thermal comfort (as defined by ASHRAE Standard 55) while minimizing energy consumption. The coil tube's consistent geometry, high thermal conductivity, and resistance to fouling are critical for maintaining the heat transfer coefficient (U-value) stability that such intelligent control systems depend upon.

5.2 Additional Application Areas

6. Quality Certifications and Standards Compliance

6.1 Applicable Standards

Standard Scope
ASTM A269 / A269M Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Pipes and Tubing
ASTM A270 / A270M Standard Specification for Austenitic Stainless Steel Pipe (Seamless and Welded)
ASME B36.19M Welded and Seamless Wrought Stainless Steel Pipe
GB/T 12771 Chinese National Standard for Stainless Steel Tubes for General Purposes
EN 10217-7 European Standard for Heat-Resistant Stainless Steel Tubes for Boilers and Heat Exchangers
ISO 9001:2015 Quality Management System Certification
ISO 3834 Requirements for Quality Requirements for Fusion Welding of Metallic Materials

6.2 Inspection and Testing Protocols

  1. Chemical Analysis: Spark Optical Emission Spectroscopy (OES) or laboratory wet chemical analysis to verify Cr, Ni, Mo, C, and other alloying element content per ASTM A269.
  2. Mechanical Testing: Tensile testing per ASTM E8/E8M and hardness testing per ASTM A262.
  3. Hydrostatic/Pneumatic Pressure Testing: Each coil is pressure-tested to verify weld integrity and absence of leaks, typically at 1.5× the maximum design pressure.
  4. Dimensional Inspection: OD, WT, and coil diameter measured at multiple points along the coil length using calibrated micrometers and ultrasonic thickness gauges.
  5. Visual and Dye Penetrant Inspection: Weld seam and surface examined for defects, cracks, or inclusions per ASTM E165.
  6. Corrosion Testing (on request): Salt spray testing (ASTM B117) or intergranular corrosion testing (ASTM A262 Practice E) for qualifying grades.

6.3 Certifications Held by Wenzhou Jixing Metal Materials Co., Ltd

7. Unique Selling Points