Stainless Steel Coil Tube (Coiltube) — Medium-Low Temperature Refrigeration Grade
Product Overview
The Stainless Steel Coil Tube (Product No. 715) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous tubular product designed specifically for medium-low temperature refrigeration systems, including cold storage units, fan coil assemblies, and heat exchange networks. The coil tube is supplied in a continuous coiled configuration, eliminating the need for butt welding during installation and significantly reducing thermal bridging, leak risk, and mechanical stress at joints.
This product represents a specialized application of austenitic stainless steel tubing technology, where the material's exceptional cryogenic toughness, corrosion resistance, and dimensional stability are leveraged to withstand prolonged exposure to refrigerant fluids, condensate, and humid cold environments. The coil tube serves as the primary heat transfer medium in evaporator and condenser circuits of industrial and commercial refrigeration equipment.
Material & Properties
Base Material Composition
The coil tube is fabricated from Austenitic Stainless Steel, conforming to grades specified under ASTM A213/A213M (Standard Specification for Seamless Austenitic Chromium- Nickel Stainless Steel Tubing for Heat-Transfer Service) and GB/T 12771 (Seamless Stainless Steel Tubes for Heat Exchangers). The primary alloy grade utilized is SAE 304 (UNS S30400), with optional availability in SAE 316L (UNS S31603) for enhanced chloride resistance in aggressive environments.
Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (304); ≥ 485 MPa (316L)
- Yield Strength (0.2% Offset): ≥ 205 MPa (304); ≥ 170 MPa (316L)
- Elongation at Break: ≥ 40% (minimum, at room temperature)
- Cryogenic Impact Toughness: Retains full ductility down to −196°C (liquid nitrogen temperature), with no brittle-to-ductile transition observed
- Hardness (Brinell): ≤ 217 HB (annealed condition)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C; increases to approximately 28 W/(m·K) at −40°C, facilitating efficient heat transfer at low temperatures
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
Corrosion Resistance
- Excellent resistance to atmospheric corrosion, condensate, and dilute organic acids
- Resistance to pitting and crevice corrosion in chloride-containing environments (316L grade: up to 1,000 ppm chloride at ambient temperature)
- Non-magnetic in the fully annealed condition (magnetic permeability ≤ 1.05)
- Compliant with NSF/ANSI 61 for potable water and food-grade contact applications
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Number | 715 | — |
| Material Grade | SAE 304 / SAE 316L (UNS S30400 / UNS S31603) | ASTM A213 / GB/T 12771 |
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (¼" – 1") | ASTM A213 Table 1 |
| Wall Thickness | 0.5 mm – 2.0 mm | ASME B36.19M |
| Coil Length | 50 m – 200 m (continuous, non-cut) | — |
| Coil Inner Diameter (ID) | 300 mm – 800 mm | — |
| Surface Finish | 2B (Cold Rolled, Annealed, Bright) or BA (Bright Annealed, Ra ≤ 0.4 μm) | ASTM A478 |
| Tolerance — OD | ± 0.1 mm (Precision Grade) | EN 10217-7 |
| Tolerance — Wall Thickness | ± 10% of nominal | ASTM A213 |
| Operating Temperature Range | −196°C to +400°C | ASME BPVC Section VIII |
| Maximum Working Pressure | ≤ 1.6 MPa (16 bar) — design dependent | EN 13456-1 |
| Refrigerant Compatibility | R-134a, R-404A, R-407C, R-507, NH₃ (anhydrous), CO₂ | ASHRAE Standard 34 |
| Hydrostatic Test Pressure | ≥ 1.5 × design pressure (per coil batch) | ASTM A213 Clause 9 |
| End Condition | Plain cut, deburred, or double-ended formed (per customer specification) | — |
Manufacturing Process
1. Raw Material Procurement & Verification
High-purity stainless steel billet or strip is sourced from certified suppliers with full Mill Test Certificates (MTC) in accordance with EN 10204 Type 3.1. Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition, ensuring chromium content ≥ 18%, nickel content ≥ 8%, and carbon content ≤ 0.08% (304) or ≤ 0.03% (316L).
2. Cold Drawing & Seamless Forming
The coil tube is produced via the seamless cold-drawing process, which involves:
- Piercing: Hot-rolled hollow billets are pierced to produce initial seamless tubes.
- Intermediate Annealing: Tubes are solution-annealed at 1050–1100°C followed by rapid water quenching to restore full austenitic microstructure and eliminate cold-work hardening.
- Cold Drawing: Tubes are drawn through precision tungsten carbide dies to achieve final OD and wall thickness dimensions with tight tolerances. Multiple drawing passes may be employed for thin-wall specifications.
- Pilot Removal: The drawing pilot (mandrel) is extracted, yielding a seamless, joint-free inner bore.
3. Final Annealing & Surface Treatment
After cold drawing, the coil tube undergoes final solution annealing at 1050–1150°C in a controlled atmosphere furnace (inert gas or vacuum) to achieve the required grain structure, dimensional stability, and corrosion resistance. The 2B finish is achieved through cold rolling and annealing with a light passivation; the BA finish involves bright annealing in a high-purity reducing atmosphere, followed by electrolytic pickling and passivation per ASTM A967.
4. Precision Coiling
The continuous tube is wound onto a coiling reel using a controlled-tension winding system to prevent ovality, kinking, or residual stress. The coil geometry is optimized to minimize bending stress during downstream installation, with minimum bend radius ≥ 5× OD for 304 grade and ≥ 6× OD for 316L grade.
5. Quality Inspection
- Visual Inspection: 100% examination for surface defects, scratches, and dimensional irregularities.
- Dimensional Measurement: OD, wall thickness, and coil diameter verified using laser micrometers and calipers at intervals of every 50 m.
- Hydrostatic Testing: Each coil subjected to water pressure testing at 1.5× working pressure for a minimum dwell time of 10 seconds.
- Eddy Current Testing (ECT): Per ASTM E309 for subsurface defect detection (voids, cracks, seams).
- Chemical & Mechanical Testing: Sampling per batch for tensile testing (ASTM E8), hardness testing, and chemical analysis (ASTM E415).
- Corrosion Testing: Pitting resistance verified via ASTM G48 (ferric chloride test) for 316L grade.
6. Packaging & Shipping
Coils are wrapped in moisture-proof polyethylene film, secured with steel strapping, and shipped on wooden pallets or in export-grade steel drums. Desiccant packs are included to prevent moisture ingress during transit. Each coil is labeled with a unique heat number, material grade, dimensions, and MTC reference.
Applications
Primary Application Domain: Medium-Low Temperature Refrigeration
The coil tube is purpose-engineered for use in fan coil units (FCUs) and evaporator assemblies operating within the medium-low temperature range of −10°C to −40°C, as characterized in performance studies of cold storage fan coil systems. Key application areas include:
- Industrial Cold Storage: Evaporator coil circuits in blast freezers, chilled warehouses, and cold rooms for food preservation (−18°C to −25°C)
- Commercial Refrigeration: Display cases, walk-in coolers, and supermarket refrigeration systems
- Pharmaceutical Cold Chain: Vaccine storage and pharmaceutical logistics requiring precise temperature control at 2°C to 8°C or ultra-low temperatures at −70°C
- Food Processing: Heat exchangers in pasteurization, pasteurization, and cryogenic freezing lines
- Marine & Offshore Refrigeration: Shipboard cold storage systems where chloride resistance is critical (316L grade)
- Industrial Heat Exchangers: Condensers and evaporators in process cooling systems for chemical, petrochemical, and power generation sectors
Performance Advantages in Refrigeration
Research on the performance of fan coil units for medium-low temperature cold storage has demonstrated that stainless steel coil tubes offer several distinct advantages over traditional copper or carbon steel alternatives:
- Superior Corrosion Longevity: Elimination of galvanic corrosion when in contact with aluminum fins, reducing maintenance intervals by up to 5× compared to copper tube assemblies
- Cryogenic Reliability: No risk of brittle fracture at sub-zero temperatures, ensuring structural integrity throughout the design life of the refrigeration system
- Hygienic Surface: Smooth, non-porous interior surface prevents bacterial adhesion and biofilm formation, critical for food-grade and pharmaceutical applications
- Weld-Free Installation: Continuous coil configuration eliminates brazing joints, reducing refrigerant leak points and improving system reliability
- Recyclability: 100% recyclable material with no loss of alloy properties upon reprocessing, supporting circular economy and sustainability goals
Quality Certifications & Compliance
International Standards
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — certified manufacturing process |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| CE Marking (EU) | Compliance with European pressure equipment directives (PED 2014/68/EU) |
| ASME Section VIII | Pressure vessel and heat exchanger components compliance |
| NSF/ANSI 61 | Health effects — materials for water systems |
| 3-A Sanitary Standards | Sanitary design for food and dairy processing equipment |
| EN 10204 3.1 | Mill Test Certificate — full chemical and mechanical analysis |
Testing & Verification Protocols
- Material Certification: Every heat lot accompanied by a Mill Test Certificate (MTC) issued per EN 10204 Type 3.1, including full chemical composition, tensile test results, and impact test data.
- Batch Traceability: Unique heat numbers and coil identifiers enable full traceability from raw material mill to end installation.
- Third-Party Inspection: Available upon request through accredited bodies including SGS, Bureau Veritas, or TÜV Rheinland.
- Refrigerant Compatibility Testing: Verified per ASHRAE Standard 34 for compatibility with all major H