Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube, manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a continuous-length tubular product supplied in coiled form. Unlike conventional straight-length seamless or welded pipes, coil tubes are wound into a large-diameter spool, enabling continuous processing, reduced material waste, and enhanced logistical efficiency. This product is particularly suited for applications requiring high-temperature resistance, corrosion resistance, and mechanical durability in HVAC systems, heat exchangers, refrigeration circuits, and fluid transport systems.
The coil tube configuration supports automated forming, cutting, and heat exchanger manufacturing processes, making it an integral component in modern industrial heat transfer and ventilation systems, including fan coil units (FCUs) where centralized and remote control systems manage thermal performance.
2. Material Composition and Properties
2.1 Base Alloy Grades
The primary material grades used in the production of this coil tube include:
- AISI 304 (UNS S30400) — Chromium-Nickel austenitic stainless steel, offering excellent general corrosion resistance and formability.
- AISI 316L (UNS S31603) — Low-carbon variant with added molybdenum (Mo) for superior resistance to pitting and crevice corrosion in chlorinated environments.
- AISI 321 (UNS S32100) — Titanium-stabilized grade providing enhanced resistance to intergranular corrosion at elevated temperatures.
2.2 Chemical Composition (Typical, wt%)
| Element | 304 | 316L | 321 |
|---|---|---|---|
| C (Carbon) | ≤ 0.08 | ≤ 0.03 | ≤ 0.08 |
| Cr (Chromium) | 18.0 – 20.0 | 16.5 – 18.5 | 17.0 – 19.0 |
| Ni (Nickel) | 8.0 – 10.5 | 10.0 – 14.0 | 9.0 – 12.0 |
| Mo (Molybdenum) | — | 2.0 – 3.0 | — |
| Ti (Titanium) | — | — | 5 × (C × 5) – 0.70 |
| Mn (Manganese) | ≤ 2.0 | ≤ 2.0 | ≤ 2.0 |
| Si (Silicon) | ≤ 0.75 | ≤ 1.00 | ≤ 0.75 |
| P (Phosphorus) | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| S (Sulfur) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
2.3 Mechanical Properties (Annealed Condition)
| Property | 304 | 316L | 321 |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 485 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ≥ 205 MPa |
| Elongation (A50mm) | ≥ 40% | ≥ 40% | ≥ 40% |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 217 |
2.4 Thermal Properties
- Thermal conductivity at 100°C: 16.3 W/(m·K) for 304 grade
- Thermal expansion coefficient (20–100°C): 17.3 × 10⁻⁶ /K
- Maximum service temperature: 870°C (304), 870°C (316L), 900°C (321)
3. Dimensional Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 25.4 mm (1/8" – 1") | ASTM A269 / EN 10216-5 |
| Wall Thickness (WT) | 0.25 mm – 1.50 mm | ASTM A269 / GB/T 14976 | Coil Length (Continuous) | 10 m – 500 m per coil | Manufacturer standard |
| Coil Core Diameter | 114 mm – 200 mm | — |
| Coil Outer Diameter (Max) | ≤ 1,200 mm | — |
| OD Tolerance | ±0.10 mm or ±0.05 mm (precision grade) | ASTM A269 |
| Wall Thickness Tolerance | ±10% or ±0.05 mm | ASTM A269 |
| Straightness | ≤ 1.5 mm/m | EN 10216-5 |
| Surface Finish | 2B, BA (Bright Annealed), or No.4 Hairline | ASTM A480 |
4. Manufacturing Process
4.1 Process Flow
- Coil Uncoiling & Straightening — The raw stainless steel strip (hot-rolled coil or cold-rolled coil) is fed from the upstream coil into a precision straightening line, eliminating residual curvature from the rolling process.
- Edge Trimming & Cleaning — Side edges are trimmed to exact width; surface contaminants (oils, oxides) are removed via alkaline cleaning or pickling to ensure uniform weld quality.
- Forming (Roll Forming) — The flat strip is passed through a series of progressively curved rollers that gradually bend the strip into a helical tube shape without material thinning or work hardening.
- Welding — The longitudinal seam is sealed using one of the following methods:
- Argon Shielded Welding (AW) — Continuous high-frequency induction or laser welding under inert gas shielding.
- Autogenous Laser Welding — High-precision laser beam welding for narrow, deep weld beads with minimal heat-affected zone (HAZ).
- Internal Weld Finishing — The internal weld bead is ground flush using a rotating ceramic or diamond tool to achieve a smooth internal surface, critical for fluid flow and heat transfer efficiency.
- Heat Treatment (Solution Annealing) — The welded tube is heated to 1,050–1,100°C in a protective atmosphere furnace, followed by controlled cooling to restore full austenitic microstructure and eliminate residual stresses.
- Pickling & Passivation — The tube is immersed in a mixed acid bath (HNO₃/HF) to remove scale, followed by passivation treatment to form a protective chromium oxide film.
- Coiling & Packaging — The finished tube is wound onto a precision core and secured with steel strapping, wrapped in protective film, and packed for shipment.
4.2 Quality Control Points
- Online ultrasonic testing (UT) for weld seam integrity
- Eddy current testing (ECT) for surface and near-surface defect detection
- Hydrostatic pressure testing at 1.5× working pressure for leak resistance verification
- Spectroscopic analysis (PMI gun) for chemical composition verification at each coil lot
- Dimensional measurement using laser diameter sensors and ultrasonic wall thickness gauges
5. Applications
5.1 HVAC & Fan Coil Units
The coil tube is a primary component in fan coil units (FCUs), where it functions as the heat exchange element in air-conditioning systems. The continuous coil form facilitates automated coil winding for both heating and cooling circuits. Centralized control and remote control systems (as referenced in industry literature) manage the thermal performance of these units, requiring high-reliability tube materials that withstand cyclic thermal loading.
5.2 Heat Exchangers
- Shell-and-tube heat exchangers
- Plate-fin heat exchangers
- Condensers and evaporators in refrigeration systems
- Air-to-water heat exchangers
5.3 Additional Applications
- Automotive exhaust systems and turbocharger piping
- Food processing and pharmaceutical piping (316L grade)
- Chemical processing systems requiring corrosion resistance
- Domestic water heating systems
- Gas appliance burners and pilot tubes
6. Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following certifications and adheres to the following standards for its coil tube products:
| Standard / Certification | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| CE Marking (EU) | Conformity with European safety directives |
| ASTM A269 / A269M | Specification for Seamless and Welded Austenitic Stainless Steel Tubing |
| EN 10216-5 | Non-alloy and alloy steel tubes for pressure purposes |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes |
| JIS G3448 | Japanese Industrial Standard for stainless steel tubes |
| ASME B31.3 | Process piping design code compliance |
7. Unique Selling Points
- Continuous Coil Format — Eliminates butt weld joints inherent in straight-length pipe assemblies, reducing potential failure points and improving system integrity.
- High Precision Dimensions — Tight OD and wall thickness tolerances ensure consistent heat transfer performance and compatibility with automated manufacturing equipment.
- Internal Weld Flushness — Achieves internal surface roughness (Ra) of ≤ 0.8 μm, critical for minimizing pressure drop and enhancing thermal efficiency in heat exchanger applications.
- Multi-Grade Availability — Offers 304, 316L, 321, and custom alloy grades to match specific service conditions including chlorinated environments, high-temperature service, and cryogenic applications.
- Scalable Production — Coil supply format supports high-volume, continuous production in downstream manufacturing, reducing labor costs and material waste by up to 15% compared to cut-length pipe.
8. Technical Notes
Note: For applications involving centralized control and remote monitoring of fan coil units, the coil tube must be selected with consideration of thermal cycling fatigue resistance. The austenitic stainless steel grades specified herein provide excellent fatigue performance under repeated thermal expansion and contraction cycles, ensuring long-term reliability in automated HVAC control systems where operating parameters are dynamically adjusted by building management systems (BMS).
Storage & Handling: Coils should be stored in a dry, well-ventilated environment at ambient temperature. Avoid contact with carbon steel surfaces to prevent galvanic corrosion. Use appropriate lifting equipment rated for the coil weight to prevent deformation during handling.