Ultra-Long Small Diameter Stainless Steel Refrigeration Coil Tube (Coil Tube)

Product Overview

The Ultra-Long Small Diameter Refrigeration Coil Tube (Product No. 1338) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered stainless steel coil tube specifically designed for high-efficiency refrigeration and heat exchange systems. This product represents a significant advancement in coil tube technology, addressing the critical challenge of manufacturing and maintaining ultra-long coil tubes with extremely small inner diameters (ID) — a domain where conventional cleaning and processing methods face severe limitations.

Building upon extensive research into Fluorine-Free Cleaning Solutions (无氟清洗方案) for ultra-long small diameter refrigeration coil tubes, this product integrates advanced surface treatment technologies that eliminate the use of halogenated fluorocarbons and hydrofluoric acid during the manufacturing and post-processing stages. This environmentally responsible approach not only reduces the environmental footprint but also ensures superior surface integrity and long-term corrosion resistance of the coil tube interior.

The coil tube is supplied in continuous coil form, enabling flexible downstream processing including cutting, bending, welding, and heat exchanger assembly without the need for additional straightening operations. The product is particularly suited for applications requiring extended tube lengths with consistent micro-diameter tolerances, such as automotive air conditioning condensers, industrial refrigeration systems, and high-performance chiller units.

Material & Properties

Base Material Composition

The coil tube is fabricated from high-purity austenitic stainless steel, with the primary grade being SUS316 (ASTM A269 TP316 / UNS S31600), supplemented by optional grades including SUS304 (UNS S30400) and SUS321 (UNS S32100) depending on application-specific requirements. The alloy composition ensures exceptional resistance to pitting corrosion, crevice corrosion, and stress corrosion cracking in aggressive refrigerant environments.

Key Chemical Composition (SUS316 Grade):

Mechanical Properties

Surface Characteristics

Following the proprietary Fluorine-Free Cleaning and Passivation Process, the internal and external surfaces of the coil tube achieve:

Specifications

Parameter Specification / Range Unit Standard Reference
Outer Diameter (OD) 3.0 – 12.0 mm ASTM A269 / GB/T 14976
Wall Thickness (WT) 0.3 – 1.5 mm —
Inner Diameter (ID) 1.0 – 10.0 mm —
OD Tolerance ±0.05 – ±0.10 mm ASTM A269
WT Tolerance ±10% of nominal — GB/T 14976
Coil Length (Continuous) Up to 3,000 m —
Minimum Bend Radius ≥ 3 × OD — —
Hydrostatic Test Pressure 6.0 – 10.0 MPa ASTM A269
Operating Pressure (Design) Up to 2.5 MPa —
Refrigerant Compatibility R134a, R410A, R32, R404A, R407C, CO₂ (R744) — ASHRAE 34
Surface Finish (Internal) Electropolished / Fluorine-Free Cleaned — ASTM A967
Surface Finish (External) Mirror Polished (Ra ≤ 0.4 μm) / Satin (Ra ≤ 0.8 μm) / Bead Blasted (Ra ≤ 1.6 μm) — —
Coil Packaging Steel core coil, shrink-wrapped, wooden pallet — —
Typical Coil Weight 500 – 2,000 kg —

Manufacturing Process

The production of the Ultra-Long Small Diameter Refrigeration Coil Tube follows a rigorous multi-stage manufacturing sequence, integrating proprietary technologies developed through extensive research into fluorine-free processing methodologies:

Stage 1: Raw Material Preparation and Hot Rolling

  1. Ingot Casting: High-purity stainless steel ingots produced via Vacuum Arc Remelting (VAR) or Electro-Slag Remelting (ESR) processes to minimize inclusions and ensure homogeneous alloy distribution.
  2. Hot Rolling: Billets are heated to 1,150°C – 1,200°C and hot-rolled into seamless tube blanks with OD tolerance of ±0.5 mm. The hot rolling schedule is precisely controlled to achieve a fine-grained, recrystallized austenitic microstructure with grain size ≤ ASTM No. 8.

Stage 2: Cold Drawing and Sizing

  1. Multi-pass Cold Drawing: The hot-rolled tube blanks undergo sequential cold drawing through progressively smaller die openings (typically 4 – 8 passes) to achieve the target small outer diameter with tight dimensional tolerances (±0.05 mm). Drawing speeds are controlled at 5 – 15 m/min to prevent work hardening-induced cracking.
  2. Intermediate Annealing: After every 2 – 3 drawing passes, the tube is solution annealed at 1,050°C – 1,100°C in a protective atmosphere (N₂ + H₂) to relieve accumulated residual stresses and restore ductility.
  3. Piercing and Mandrel Drawing: For tubes with ID < 3.0 mm, the piercing method with a carbide mandrel is employed to precisely control the inner diameter and wall thickness uniformity, achieving WT variation ≤ ±5% along the entire tube length.

Stage 3: Coiling and Straightening

  1. Continuous Coiling: The drawn tubes are wound onto precision steel cores (typically 114 mm or 168 mm core diameter) using a controlled tension coiling system to produce continuous coil lengths up to 3,000 meters without joints or splices.
  2. Post-Coil Straightening: Individual tube segments, if required, are straightened using a multi-roller straightener with straightening accuracy of ≤ 0.3 mm/m.

Stage 4: Fluorine-Free Cleaning and Surface Treatment (Proprietary Technology)

  1. Pre-Cleaning: Mechanical removal of drawing lubricants and residual debris through ultrasonic cleaning in alkaline aqueous solutions (pH 10 – 12) at 60°C – 80°C. This replaces traditional acid pickling with hydrofluoric acid (HF).
  2. Chemical Cleaning (Fluorine-Free Formulation): The core innovation involves a proprietary non-fluorine-based cleaning solution composed of organic complexing agents (e.g., citric acid, oxalic acid derivatives) combined with chelating surfactants. This formulation effectively dissolves oxide scale and iron contamination without introducing fluoride ions, which are known to cause stress corrosion cracking (SCC) in austenitic stainless steels under refrigerant service conditions.
  3. Electropolishing: The tube interior undergoes electropolishing at current density of 40 – 80 A/dm² in a phosphoric acid-based electrolyte (without HF) to achieve surface roughness Ra ≤ 0.4 μm. This process simultaneously removes surface defects, burrs, and residual contaminants, creating a mirror-smooth internal surface critical for minimizing refrigerant flow resistance.
  4. Passivation: Final passivation is performed using a citric acid or nitric acid-based solution (HF-free) to form a uniform, adherent chromium oxide passive film (2 – 5 nm thick). The passivation effectiveness is verified by the Copper Sulfate Test (CST) per ASTM A967, with a minimum passivation time of 60 minutes.
  5. Purification Rinse and Drying: Triple rinse with deionized water (conductivity ≤ 1 μS/cm) followed by hot air drying at 80°C – 100°C to prevent water spot formation.

Stage 5: Quality Inspection and Packaging

  1. Dimensional Inspection: 100% online measurement of OD and WT using laser diameter gauges and ultrasonic wall thickness sensors, with data logging and statistical process control (SPC).
  2. Leak Testing: Hydrostatic pressure testing at 1.5 × design pressure for a minimum hold time of 30 seconds per coil.
  3. Surface Inspection: Visual inspection under 10× magnification and automated optical scanning for surface defects (pits, scratches, inclusions).
  4. Internal Cleanliness Verification: Particle count analysis using liquid flow-through filtration method; contamination levels verified per ISO 4406.
  5. Corrosion Testing: Salt spray testing (ASTM B117) for ≥ 500 hours with no pitting or general corrosion; intergranular corrosion testing per ASTM A262 Practice E.
  6. Packaging: Coils are shrink-wrapped with moisture-absorbent desiccant packs, labeled with product identification, heat number, and traceability codes, and secured on wooden pallets for shipping.

Applications

The Ultra-Long Small Diameter Stainless Steel Refrigeration Coil Tube is engineered for demanding applications where reliability, corrosion resistance, and thermal efficiency are paramount:

Primary Applications