Stainless Steel Coil Tube — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed for demanding thermal-fluid applications, particularly in Fan Coil Unit (FCU) systems and Capillary Tube Network (CTN) integrated heat pump systems operating in severe cold regions. The coil tube is supplied in a coiled configuration, enabling efficient storage, transportation, and on-site installation with minimal cutting and welding.
Distinct from conventional straight-length stainless steel tubing, the coil tube maintains dimensional integrity and surface finish throughout the coiling process, offering superior performance in heat exchange applications where flow uniformity and thermal efficiency are critical.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is fabricated from high-grade austenitic stainless steel, meeting or exceeding the following material standards:
- ASTM A269 / ASME SA-269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service
- ASTM A312 / ASME SA-312 — Standard Specification for Seamless and Welded Austenitic Chromium-Chromium-Nickel Stainless Steel Tubing for Higher Temperature Service
- GB/T 12771 — Chinese National Standard for Stainless Steel Tubes for Fluid Transport
2.2 Common Grade Designations
- 304 (UNS S30400) — Chromium-Nickel austenitic grade with excellent general corrosion resistance
- 316 (UNS S31600) — Molybdenum-enhanced grade with superior resistance to pitting and crevice corrosion
- 316L (UNS S31603) — Low-carbon variant of 316 for enhanced weldability and resistance to sensitization
- 321 (UNS S32100) — Titanium-stabilized grade for elevated-temperature applications
2.3 Key Mechanical and Physical Properties
| Property | 304 Grade | 316 Grade | 316L Grade |
|---|---|---|---|
| Chromium (Cr) Content | 18.0–20.0% | 16.0–18.0% | 16.0–18.0% |
| Nickel (Ni) Content | 8.0–10.5% | 10.0–14.0% | 10.0–14.0% | Molybdenum (Mo) Content | — | 2.0–3.0% | 2.0–3.0% |
| Carbon (C) Maximum | 0.08% | 0.08% | 0.03% |
| Tensile Strength (Minimum) | 515 MPa (75 ksi) | 515 MPa (75 ksi) | 485 MPa (70 ksi) |
| Yield Strength (0.2% Offset) | 205 MPa (30 ksi) | 205 MPa (30 ksi) | 170 MPa (25 ksi) |
| Elongation (% in 50 mm) | ≥40% | ≥40% | ≥45% |
| Density | 8.00 g/cm³ | 8.03 g/cm³ | 8.03 g/cm³ |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | 14.6 W/(m·K) |
2.4 Corrosion Resistance
All grades exhibit outstanding resistance to atmospheric corrosion, aqueous environments, and mild chemical media. The 316 and 316L grades demonstrate significantly enhanced resistance to chlorides, making them ideal for coastal or industrial environments. The passive chromium oxide film self-heals in the presence of oxygen, providing long-term protection against oxidation and scaling.
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ25.4 mm (1/8" – 1") | ASTM A269 Table 3 |
| Wall Thickness | 0.25 mm – 3.0 mm | ASTM A269 / A312 |
| Coil Length (per Spool) | 50 m – 500 m (customizable) | Manufacturer Specification |
| Coil Diameter | Φ100 mm – Φ600 mm | Manufacturer Specification |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed, Mirror | ASTM A478 |
| Manufacturing Method | Seamless / Welded (ERW, TIG) | ASTM A269 / A312 |
| End Condition | Plain, Beveled, Threaded, or Custom | Customer Requirement |
| Tolerance — OD | ±0.05 mm (Precision) / ±0.10 mm (Standard) | ASTM A269 |
| Tolerance — Wall Thickness | ±0.02 mm (Precision) / ±0.05 mm (Standard) | ASTM A269 |
| Operating Temperature Range | −196°C to +650°C | Material Data Sheet |
| Maximum Operating Pressure | Up to 30 MPa (depending on OD and wall thickness) | ASME B31.3 |
| Hydrostatic Test Pressure | 1.5× Maximum Working Pressure (minimum 2.5 MPa) | ASME B31.3 |
| Heat Treatment | Solution Annealing (1010–1150°C) followed by Water Quench | ASTM A269 |
4. Manufacturing Process
4.1 Seamless Coil Tube Production
- Hot Rolling: Billet is heated to approximately 1200°C and hot-rolled into a hollow tube blank.
- Piercing and Elongation: The blank is pierced and elongated through a series of passes to achieve intermediate dimensions.
- Hot Finishing: Further reduction in a hot finishing mill to approach final dimensions.
- Cold Drawing / Cold Rolling: The tube is drawn through precision dies or cold-rolled to achieve exact OD, wall thickness, and surface finish.
- Solution Annealing: The tube is heated to 1010–1150°C in a controlled atmosphere and rapidly quenched to restore full solution-annealed microstructure and mechanical properties.
- Acid Pickling and Passivation: Removal of scale and formation of a uniform passive chromium oxide film.
- Coiling: The tube is wound onto a precision-controlled coiler at controlled tension to maintain dimensional accuracy and prevent ovality.
4.2 Welded Coil Tube Production
- Strip Preparation: Precision-cut stainless steel strip is inspected for surface quality and dimensional tolerances.
- Forming: The flat strip is progressively formed into a tubular shape through a series of rolls.
- Welding: The seam is welded using Electric Resistance Welding (ERW) or Tungsten Inert Gas (TIG) welding with argon shielding.
- Seam Inspection: The weld seam is inspected via ultrasonic testing (UT) or eddy current testing (ECT) to ensure weld integrity.
- Piercing and Sizing: The welded tube is pierced and cold-worked to final dimensions.
- Annealing, Pickling, and Coiling: As described in the seamless process above.
5. Applications
5.1 Fan Coil Unit (FCU) Systems
Stainless steel coil tubes serve as the primary heat exchange element in fan coil units used for space heating and cooling. The coil tube's excellent thermal conductivity and corrosion resistance ensure efficient heat transfer between the circulating fluid (water or refrigerant) and the air stream. In severe cold regions, the coil tube withstands extreme thermal cycling and the corrosive effects of de-icing fluids and humid indoor environments.
5.2 Capillary Tube Network (CTN) Integrated Heat Pump Systems
In combined FCU and CTN heat pump systems, stainless steel coil tubes are deployed as the capillary network elements embedded within building envelopes (walls, ceilings, floors). These systems provide radiant heating and cooling with high thermal comfort and energy efficiency. Key advantages of stainless steel coil tubes in CTN applications include:
- Low flow resistance: Smooth interior surface finish minimizes pressure drop across the capillary network
- Thermal expansion compatibility: Coefficient of thermal expansion matches common building materials
- Long service life: Resistance to corrosion eliminates the risk of system leakage over decades of operation
- Hygienic properties: Non-toxic, non-leaching, and resistant to biofilm formation
5.3 Additional Applications
- Refrigeration and air conditioning (HVAC) coil assemblies
- Automotive radiator and condenser tubes
- Chemical processing and pharmaceutical piping
- Food and beverage processing equipment
- Medical device and instrument tubing
- Heat exchanger bundles and shell-and-tube designs
- Hydroponic and agricultural irrigation systems
6. Quality Certifications and Testing
6.1 Certifications
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- CE Marking — European Conformity for pressure equipment and construction products
- NADCAP — National Aerospace and Defense Contractors Accreditation Program (for aerospace-grade applications)
- PED (Pressure Equipment Directive 2014/68/EU) — Compliance for pressure-containing components
6.2 Incoming Material Inspection
- Spectroscopic chemical analysis (OES) for alloy composition verification
- Visual surface inspection for defects, inclusions, and surface imperfections
- Mill test certificate (MTC) / EN 10204 3.1 or 3.2 documentation
6.3 In-Process Quality Control
- Dimensional inspection at each cold-working stage (OD, wall thickness, ovality)
- Ultrasonic testing (UT) for internal defects and wall thickness verification
- Eddy current testing (ECT) for surface and near-surface flaw detection
- Weld seam inspection via radiographic testing (RT) or ultrasonic testing (UT)
6.4 Final Product Testing
- Hydrostatic Pressure Test: Each coil is pressure-tested at 1.5× maximum working pressure to verify leak tightness
- Chemical Analysis: Confirmation of final alloy composition per ASTM B751
- Mechanical Testing: Tensile, hardness (Rockwell B), and elongation testing per ASTM A312
- Corrosion Testing: Salt spray testing (ASTM B117) and intergranular corrosion testing (ASTM A262 Practice E) for applicable grades
- Surface Finish Verification: Ra (roughness average) measurement via surface profilometry
- Visual Inspection: Final inspection for surface defects, coiling marks, and dimensional conformity
7. Unique Selling Points
- Severe Cold Region Performance: Engineered for reliable operation in extreme low-temperature environments (down to −60°C), validated through research on FCU and CTN integrated heat pump systems in harsh climates
- Precision Coiling Technology: Advanced coiling process ensures consistent tube geometry with minimal ovality and residual stress, enabling seamless integration into heat exchanger and capillary network assemblies
- Customizable Specifications: Wide range of OD, wall thickness, grade, and surface finish options with custom coil lengths to meet project-specific requirements
- Full Traceability: Each coil is accompanied by a comprehensive test report and material traceability documentation from mill to delivery
- Extended Service Life: Superior corrosion resistance eliminates the need for replacement, reducing lifecycle costs by an estimated 40–60% compared to carbon steel alternatives
- Sustainability: 100% recyclable material with low embodied carbon; compatible with energy-efficient heat pump systems that reduce building energy consumption
8. Packaging and Delivery
Coil tubes are wound onto wooden or steel cores, wrapped with protective plastic film or VCI (Vapor Corrosion Inhibitor) paper, and secured with steel strapping. Each coil is labeled with a unique identification tag including product grade, dimensions, heat number, coil length, and manufacturing date. Standard packaging supports international sea-freight and inland transportation in compliance with ISO 11607 handling requirements.
9. Storage and Handling Recommendations
- Store in a dry, well-ventilated indoor