Ultra-Long Small-Bore Stainless Steel Refrigeration Coil Tube
1. Product Overview
The Ultra-Long Small-Bore Stainless Steel Refrigeration Coil Tube is a precision-engineered tubular product designed specifically for high-efficiency refrigeration and heat exchange systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube is characterized by its exceptionally long continuous length and small inner diameter, making it ideal for applications demanding compact heat transfer surfaces with minimal refrigerant charge. The product represents a significant advancement in refrigeration technology, particularly in the context of fluorine-free (HFC-free) cleaning solutions that eliminate the use of ozone-depleting and greenhouse-gas-emitting refrigerants during the manufacturing and maintenance processes.
This product line addresses the growing global demand for environmentally sustainable refrigeration systems that comply with international regulations such as the Montreal Protocol and the Kigali Amendment. The integration of fluorine-free cleaning protocols into the production workflow ensures that the coil tubes are free from residual fluorinated compounds, thereby contributing to a reduced environmental footprint throughout the product lifecycle.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade stainless steel, with primary alloy grades including:
- AISI 304 (UNS S30408) — The most widely used austenitic stainless steel, offering excellent corrosion resistance, formability, and weldability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 (UNS S31608) — Enhanced corrosion resistance due to the addition of 2–3% Molybdenum (Mo), making it suitable for aggressive chemical environments and marine applications.
- AISI 321 (UNS S32108) — Stabilized with Titanium (Ti) to prevent intergranular corrosion during welding, suitable for high-temperature refrigeration systems.
- AISI 316L (UNS S31603) — Low-carbon variant of 316 with superior resistance to pitting and crevice corrosion, ideal for cryogenic applications.
2.2 Mechanical Properties
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa (AISI 304); ≥ 550 MPa (AISI 316) | ASTM A269 / ASTM E8 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ASTM E8 |
| Elongation at Break | ≥ 40% | ASTM E8 |
| Hardness (Rockwell B) | 80 – 95 HRB (annealed condition) | ASTM E18 |
| Density | ~8.0 g/cm³ | — |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) (AISI 304) | ASTM E153 |
| Operating Temperature Range | −196°C to +450°C | — |
2.3 Corrosion Resistance
The austenitic stainless steel construction provides outstanding resistance to:
- Atmospheric corrosion — Suitable for outdoor and indoor environments without additional coating.
- Chemical corrosion — Resistant to dilute acids, alkalis, and organic solvents commonly encountered in refrigeration systems.
- Pitting and crevice corrosion — Particularly in AISI 316 and 316L grades due to Molybdenum content.
- Intergranular corrosion — Mitigated through proper annealing and stabilization treatments.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 12.7 mm (1/8" – 1/2") | ASTM A269 / GB/T 14976 |
| Wall Thickness | 0.3 mm – 1.5 mm | ASTM A269 |
| Inner Diameter (ID) | 2.0 mm – 10.0 mm | — |
| Coil Length (Continuous) | 50 m – 300 m per coil | — |
| Coil Diameter (Wound) | 300 mm – 600 mm | — |
| Bend Radius (Minimum) | ≥ 3× OD (cold bending) | — |
| Surface Finish | Pickled & Passivated (2B finish); Ra ≤ 0.8 μm | ASTM A380 / GB/T 12451 |
| Dimensional Tolerance (OD) | ±0.1 mm (±1.0%) | ASTM A269 |
| Dimensional Tolerance (Wall) | ±10% | ASTM A269 |
| End Condition | Plain cut; optionally beveled or threaded | — |
| Residual Stress Level | ≤ 50 MPa (after stress-relief annealing) | — |
| Fluorine Content (Post-Cleaning) | ≤ 0.1 ppm (fluorine-free verified) | Internal QC Protocol |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Incoming Inspection — High-purity stainless steel strip or seamless tube blanks are sourced from certified mills. Incoming materials undergo spectroscopic analysis (Optical Emission Spectrometry, OES) to verify chemical composition, and ultrasonic testing (UT) to detect internal defects.
- Coiling & Straightening — The stainless steel strip or tube is unwound, straightened using precision roller straighteners, and fed into the forming line. Tension control ensures uniform wall thickness throughout the length.
- Cold Forming / Seamless Drawing — For seamless tubes, the material is drawn through a series of progressively reducing dies to achieve the target small bore diameter. For welded tubes, the strip is cold-formed into a tubular shape and resistance-welded along the longitudinal seam.
- Weld Seam Inspection (if applicable) — The weld seam is inspected using automated optical sensors and, where required, X-ray or eddy current testing to ensure weld integrity and absence of porosity, cracks, or incomplete fusion.
- Heat Treatment & Annealing — The formed tubes undergo solution annealing at 1050°C – 1150°C followed by controlled cooling to restore the austenitic microstructure, relieve residual stresses, and ensure uniform mechanical properties. Stress-relief annealing at 850°C – 900°C may be applied for ultra-long coils to minimize springback during downstream bending.
- Pickling & Passivation — The tubes are subjected to acid pickling (using a mixture of nitric acid and hydrofluoric acid in controlled concentrations) to remove scale and oxidation. This is followed by passivation treatment to form a protective chromium oxide layer. Critical Note: The fluorine-containing acid is thoroughly rinsed and neutralized in this step, and subsequent cleaning protocols ensure complete removal of all fluorine residues.
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Fluorine-Free Cleaning (Proprietary Process) — This is the core innovation of the product line. A specialized fluorine-free cleaning solution is applied to remove any residual contaminants from the pickling and passivation stages. The cleaning protocol utilizes:
- Aqueous alkaline cleaning — Using sodium hydroxide (NaOH) and chelating agents at controlled pH (11–13) and temperature (60°C–80°C) to dissolve organic and inorganic residues.
- Deionized water rinsing — Multi-stage rinsing with deionized water (conductivity ≤ 5 μS/cm) to achieve ultra-low residual contamination.
- Steam sterilization — Final treatment with saturated steam at 121°C for 30 minutes to ensure microbiological cleanliness and complete removal of volatile residues.
- Fluorine detection verification — Post-cleaning samples are analyzed using ion chromatography (IC) to confirm fluorine levels below 0.1 ppm.
- Coiling & Packaging — The cleaned tubes are wound into coils of specified diameter using a precision coiling machine with uniform tension control. Coils are wrapped in protective film and packaged in wooden or steel crates to prevent mechanical damage and moisture ingress during transportation.
- Final Quality Inspection — Each batch undergoes comprehensive quality assurance including dimensional measurement (OD, wall thickness, straightness), surface inspection, hydrostatic pressure testing (typically at 1.5× working pressure for 10 seconds with no leakage), and chemical composition verification.
4.2 Key Process Parameters
| Process Step | Key Parameter | Control Range |
|---|---|---|
| Solution Annealing | Temperature / Time | 1050–1150°C / 1–2 hours |
| Stress-Relief Annealing | Temperature / Time | 850–900°C / 1–3 hours |
| Pickling | Acid Concentration / Temperature | HNO₃ 20–30% + HF 2–5% / 60–80°C |
| Fluorine-Free Cleaning | pH / Temperature / Time | pH 11–13 / 60–80°C / 20–40 min |
| Hydrostatic Testing | Test Pressure / Hold Time | 1.5× Working Pressure / ≥ 10 sec |
5. Applications
The Ultra-Long Small-Bore Stainless Steel Refrigeration Coil Tube finds extensive application across multiple industries:
5.1 Refrigeration & Air Conditioning (HVAC)
- Evaporator and condenser coils in commercial and industrial refrigeration units
- Heat exchangers in chiller systems and heat pumps
- Capillary tubes and metering devices in vapor-compression refrigeration cycles
- Cooling coils in data center thermal management systems
5.2 Food & Beverage Industry
- Refrigeration systems for food processing, storage, and transportation
- Cooling coils in breweries, dairies, and cold chain logistics
- Heat exchangers for pasteurization and sterilization processes (CIP-compatible due to fluorine-free cleaning)
5.3 Pharmaceutical & Biotechnology
- Cooling systems for bioreactors, fermentation tanks, and cold storage of vaccines and biologics
- Cryogenic heat exchangers for liquid nitrogen and liquid oxygen handling
- Precision temperature control in laboratory refrigeration equipment
5.4 Chemical & Petrochemical Industry
- Heat exchangers for cryogenic distillation and separation processes
- Refrigeration systems for chemical reaction temperature control
- Corrosion-resistant cooling coils in aggressive chemical environments (AISI 316/316L grades)
5.5 Marine & Offshore
- Refrigeration systems for shipboard cargo holds and cold storage
- Heat exchangers in offshore platform cooling systems
- Corrosion-resistant coil tubes for seawater-cooled systems
5.6 Automotive & Transportation
- Refrigerated transport trailers and container cooling units
- Automotive air conditioning evaporator and condenser coils
- Battery thermal management systems in electric vehicles (EV)
6. Quality Certifications & Compliance
The Ultra-Long Small-Bore Stainless Steel Refrigeration Coil Tube is manufactured in strict compliance with international and national standards: