Stainless Steel Coil Tube (Coiltube) — Refrigeration & HVAC Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product supplied in continuous coil form, specifically designed for use in refrigeration compressors, fan coil units (FCU), air handling systems, and heat exchanger assemblies. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product conforms to the technical requirements established in the national standards for refrigeration compressors and fan coil units, as promulgated through the standards dissemination and implementation framework in the Chinese HVACR (Heating, Ventilation, Air Conditioning, and Refrigeration) industry.
Coiltube products offer significant advantages over straight-tube alternatives, including reduced material waste, improved production efficiency, superior dimensional consistency, and enhanced flexibility during downstream forming operations such as bending, coiling, and heat exchanger fin-tube assembly.
2. Material & Properties
2.1 Base Alloy Grades
- Austenitic Stainless Steel (奥氏体不锈钢): Grades 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), and 316L (UNS S31603) are the primary material options, offering excellent corrosion resistance, formability, and weldability.
- Specific Application Grades: 321 (UNS S32100) for high-temperature service environments; 309 (UNS S30900) for cryogenic and extreme thermal cycling applications in refrigeration systems.
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa (Grade 304); ≥ 485 MPa (Grade 304L) | ASTM A213 / GB/T 12771 |
| Yield Strength (屈服强度) | ≥ 205 MPa (0.2% Offset) | ASTM A213 |
| Elongation (延伸率) | ≥ 40% (at 50 mm gauge length) | ASTM A213 |
| Hardness (硬度) | ≤ 220 HV (Annealed Condition) | ASTM E92 |
| Cold Bending Performance (冷弯性能) | No cracking at 180° bend, bend radius ≥ 1D | GB/T 12771 |
2.3 Chemical Composition (Typical — Grade 304)
| Element | Maximum (%) | Element | Maximum (%) |
|---|---|---|---|
| C (Carbon) | 0.08 | Si (Silicon) | 1.00 |
| Mn (Manganese) | 2.00 | P (Phosphorus) | 0.045 |
| S (Sulfur) | 0.030 | Cu (Copper) | 0.15 |
| Cr (Chromium) | 18.00–20.00 | Ni (Nickel) | 8.00–10.50 |
2.4 Corrosion Resistance
The austenitic stainless steel coil tube demonstrates exceptional resistance to atmospheric corrosion, pitting corrosion in chloride-containing environments (particularly Grade 316L with 2.0–2.5% Mo), intergranular corrosion (especially low-carbon "L" grades), and stress corrosion cracking under normal refrigeration operating conditions. The passive chromium oxide film (Cr₂O₃) provides a self-healing protective barrier against moisture, refrigerant condensates, and mild chemical exposure common in HVACR applications.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (1/4" – 1") | ASTM A213 / GB/T 12771 |
| Wall Thickness (WT) | 0.30 mm – 1.50 mm | — |
| OD Tolerance | ±0.10 mm (for OD ≤ 12.7 mm); ±0.15 mm (for OD > 12.7 mm) | ASTM A213 |
| Wall Thickness Tolerance | ±10% of nominal | ASTM A213 |
| Coil Inner Diameter (ID) | 150 mm – 400 mm | — |
| Coil Length per Spool | 100 m – 1,000 m (customizable) | — |
| Surface Finish | Bright Annealed (BA), 2B, or Polished (Ra ≤ 0.4 μm) | ASTM A696 |
| End Condition | Plain cut, beveled, or plug-capped | — |
| Operating Temperature Range | −196 °C to +800 °C (Grade 304/316) | — |
| Maximum Working Pressure | Up to 4.0 MPa (dependent on OD and WT) | EN 13480 / ASME B31.5 |
4. Manufacturing Process
4.1 Process Flow
- Strip Preparation: Cold-rolled stainless steel strip is inspected for surface quality, chemical composition, and mechanical properties prior to forming.
- Tube Forming (Roll Forming / Welding): The strip is shaped into a tubular profile using precision roll forming equipment, followed by seamless weld formation via TIG (Tungsten Inert Gas) welding or laser welding technology.
- Heat Treatment (Solution Annealing): Continuous or batch annealing at 1,050–1,150 °C followed by controlled cooling (air or water quench) to restore full austenitic microstructure and eliminate residual stresses.
- Pickling & Passivation: Immersion in nitric/hydrofluoric acid bath to remove scale and oxide, followed by passivation treatment to establish a stable chromium oxide surface film.
- Surface Finishing: Electropolishing, mechanical polishing, or bright annealing in a reducing atmosphere (H₂/N₂) to achieve the required surface roughness and appearance.
- Precision Sizing: Internal and external sizing through calibrating rolls to ensure dimensional accuracy within specified tolerances.
- Coiling & Packaging: The finished tube is wound onto precision-machined coil cores with protective interleaving material, then shrink-wrapped or placed in wooden cases for shipment.
4.2 Quality Control Milestones
- Incoming material inspection (chemical analysis, mechanical testing)
- In-process dimensional monitoring via laser micrometers and ultrasonic thickness gauges
- Weld seam integrity verification through dye penetrant testing (DPT) or ultrasonic testing (UT)
- Final hydrostatic testing at 1.5× the maximum working pressure with a minimum dwell time of 30 seconds
- Surface defect inspection using automated visual or eddy current systems
5. Applications
5.1 Primary Application Domains
- Refrigeration Compressors (制冷压缩机): Suction and discharge piping, oil separator coils, and internal heat exchanger circuits within hermetic, semi-hermetic, and scroll-type compressors operating with R134a, R410A, R404A, R32, and natural refrigerants.
- Fan Coil Units (风机盘管): Refrigerant circuit tubing, condensate drain lines, and heat exchanger coils in residential and commercial FCU systems compliant with GB/T 19232 and EN 1395 standards.
- Heat Exchangers (换热器): Fin-and-tube heat exchangers for air-cooled condensers, evaporators, and economizers in central air conditioning and industrial refrigeration systems.
- Automotive Air Conditioning: Evaporator and condenser tubing for vehicle HVAC systems requiring high corrosion resistance and lightweight construction.
- Food & Beverage Processing: Sanitary-grade piping and heat exchanger tubing for dairy, brewing, and pharmaceutical processing equipment (Grade 316L preferred).
- Marine & Offshore: Refrigeration and HVAC systems on vessels and offshore platforms exposed to high-chloride marine environments.
5.2 Standards Compliance for Refrigeration Applications
The stainless steel coil tube is designed to meet the technical requirements specified in the Refrigeration Compressor Standards Dissemination and Implementation Guidelines (制冷压缩机标准宣贯) and the Fan Coil Unit Technical Specifications (风机盘管标准), ensuring compatibility with compressor manufacturers' design parameters and system-level performance requirements.
6. Quality Certifications
| Certification / Standard | Scope | Issuing Body |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Third-party certification body |
| ISO 14001:2015 | Environmental Management System | Third-party certification body |
| EN 10204 3.1 | Material Test Certificate | Independent inspection body |
| ASTM A213 | Seamless and Welded Austenitic Stainless Steel Tubing | ASTM International |
| GB/T 12771 | Stainless Steel Seamless Tubes for General Purposes | Standardization Administration of China (SAC) |
| ASME B31.5 | Process Piping — Material Selection & Design | American Society of Mechanical Engineers |
| NSF 61 | Drinking Water System Components — Health Effects (where applicable) | NSF International |
| RoHS / REACH | Restricted Substances / Chemical Regulation Compliance | EU Regulatory Framework |
7. Unique Selling Points
- Seamless Coil Configuration: Eliminates field welding joints, reducing leak risk and maintenance requirements in closed-loop refrigeration circuits.
- Superior Formability: High elongation values (≥ 40%) enable complex multi-pass bending and U-bend formation without cracking, critical for compact heat exchanger designs.
- Full Traceability: Each coil spool is serialized with batch-specific material test certificates (MTC), enabling complete supply chain traceability from mill to end application.
- Low-Carbon "L" Grade Availability: Grades 304L and 316L with carbon content ≤ 0.03% provide immunity to intergranular corrosion during welding operations in downstream fabrication.
- Standards-Aligned Design: Product specifications are aligned with the refrigeration compressor and fan coil unit national standards framework, ensuring direct compatibility with certified HVACR system components.
- Environmental Sustainability: Stainless steel is 100% recyclable without degradation of material properties, supporting circular economy objectives in HVACR equipment manufacturing and end-of-life disposal.