Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, designed for use in thermal transfer systems, HVAC (Heating, Ventilation, and Air Conditioning) applications, and industrial heat exchange assemblies. The coil tube is supplied in a continuous wound coil configuration, enabling efficient downstream processing such as forming, cutting, bending, and welding without the introduction of stress discontinuities associated with straight-length stock.
This product line is particularly suited for integration into fan coil unit (FCU) systems, where the coil tube serves as the primary heat transfer medium. The continuous coil form factor minimizes material waste, reduces joint points, and enhances overall thermal efficiency by maintaining uniform wall thickness and internal surface finish along the entire tube length.
Unique Selling Points: Continuous coil supply eliminates butt-weld seams; superior corrosion resistance of austenitic stainless steel grades; consistent dimensional tolerance across the coil length; compatibility with both hydronic and refrigerant-based heat exchange circuits.
2. Material & Properties
2.1 Base Material Grades
- 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance in atmospheric and mildly aggressive environments. Chromium (Cr) content: 18–20%; Nickel (Ni) content: 8–10%.
- 316 (UNS S31600) — Enhanced corrosion resistance due to Molybdenum (Mo) addition (2–3%), suitable for chemical processing, marine, and high-chloride environments.
- 321 (UNS S32100) — Columbium (Cb/Ti) stabilized grade offering superior resistance to intergranular corrosion at elevated temperatures (up to 870°C).
2.2 Mechanical Properties (Austenitic Annealed Condition)
| Property | Grade 304 | Grade 316 | Grade 321 |
|---|---|---|---|
| Tensile Strength (Minimum) | 515 MPa (75 ksi) | 515 MPa (75 ksi) | 515 MPa (75 ksi) |
| Yield Strength (0.2% Offset) | 205 MPa (30 ksi) | 170 MPa (25 ksi) | 205 MPa (30 ksi) |
| Elongation (in 50 mm / 2") | ≥40% | ≥40% | ≥40% |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | 16.3 W/(m·K) |
| Specific Heat (at 20°C) | 500 J/(kg·K) | 500 J/(kg·K) | 500 J/(kg·K) |
| Density | 8.00 g/cm³ | 8.00 g/cm³ | 8.00 g/cm³ |
| Maximum Operating Temperature | 870°C (1600°F) | 870°C (1600°F) | 900°C (1650°F) |
2.3 Surface Finish Options
- 2B Finish — Cold-rolled, annealed, and pickled; matte appearance; suitable for general industrial applications.
- No. 4 Brushed Finish — Uniform unidirectional grain; decorative and functional for HVAC assemblies.
- Electrolytic Polished (EP) Finish — Ra ≤ 0.2 μm; hygienic grade for food processing and pharmaceutical applications.
- Pickled & Passivated — Removal of oxide scale and formation of a protective chromium oxide layer for maximum corrosion resistance.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.00 mm – Φ50.80 mm (¼" – 2") | ASTM A554 / GB/T 12771 |
| Wall Thickness | 0.50 mm – 3.00 mm | ASTM A554 / GB/T 12771 | OD Tolerance | ±0.05 mm (standard); ±0.02 mm (precision) | ISO 6508 |
| Wall Thickness Tolerance | ±10% (standard); ±7% (precision) | ISO 6508 |
| Coil Inner Diameter | Φ200 mm / Φ250 mm / Φ300 mm (custom available) | — |
| Coil Length (per coil) | 50 m – 500 m (continuous) | — |
| Coil Weight | 50 kg – 2,000 kg (per coil) | — |
| Heat Treatment | Solution Annealed at 1050–1150°C, followed by water quench | ASTM A554 |
| Formability | Excellent; suitable for deep drawing, bending, and mandrel-free forming | — |
| Weldability | Excellent; compatible with TIG (GTAW), MIG (GMAW), and orbital welding | ASME BPVC Section IX |
| End Condition | Plain cut / beveled / flared / threaded (on request) | — |
4. Manufacturing Process
4.1 Production Flow
- Material Procurement: Hot-rolled stainless steel strip (HRP — Hot Rolled Pickled) sourced from certified mills, conforming to ASTM A480 / GB/T 4237 chemical composition requirements.
- Strip Preparation: Precision slitting and leveling of the cold-rolled strip to achieve target width and flatness (within ±0.5 mm/m).
- Forming (Coil Pipe Mill): The strip is fed through a multi-roll forming station (typically 12–16 passes) to progressively shape it into a circular cross-section. Roll sets are CNC-adjusted for dimensional accuracy.
- Welding: Longitudinal weld is created via Automatic Submerged Arc Welding (SAW) or Laser Welding. Laser welding is preferred for high-purity applications, producing a weld seam with minimal heat-affected zone (HAZ).
- Weld Seam Inspection: 100% ultrasonic (UT) and eddy current (EC) testing of the weld seam to detect porosity, lack of fusion, or seam offset.
- Solution Annealing: Tubes are annealed at 1050–1150°C in a continuous belt furnace or batch furnace under protective atmosphere (hydrogen or argon) to restore full austenitic microstructure and relieve forming stresses.
- Pickling & Passivation: Acid bath treatment (nitric/hydrofluoric acid blend) removes oxide scale; subsequent passivation establishes a Cr₂O₃ protective film.
- Final Dimensional Inspection: Optical OD gauging, wall thickness measurement (ultrasonic), and roundness verification at intervals along the coil.
- Coiling & Packaging: Tubes are wound onto precision-machined coil cores and packaged with protective end caps, VCI (Volatile Corrosion Inhibitor) paper wrapping, and wooden or steel coil crates for export.
4.2 Quality Control Milestones
- Incoming Material Inspection: Certificate of Analysis (COA) verification, chemical composition confirmation via optical emission spectrometry (OES).
- In-Process Inspection: Real-time OD and wall thickness monitoring with automatic deviation alarms.
- Non-Destructive Testing (NDT): 100% weld seam inspection; hydrostatic pressure testing at 3.0× working pressure for a minimum of 60 seconds per test section.
- Final Product Testing: Mechanical testing (tensile, hardness), corrosion testing (salt spray per ASTM B117, minimum 1000 hours for 316 grade), and dimensional audit.
5. Applications
5.1 HVAC — Fan Coil Unit (FCU) Systems
The primary application domain for this coil tube product is in fan coil units, which are terminal air-handling devices used in commercial and residential building HVAC systems. The coil tube functions as the heat exchanger core, transferring thermal energy between the circulating fluid (hot water, chilled water, or refrigerant) and the passing air stream. Key selection parameters for FCU coil tube design include:
- Heat Transfer Efficiency: Stainless steel's thermal conductivity and low fouling tendency ensure high heat transfer coefficients over the service life.
- Pressure Drop: Internal surface smoothness (Ra ≤ 0.4 μm) minimizes turbulent flow losses within the tube bundle.
- Corrosion Resistance: Essential for systems using glycol-based heat transfer fluids or in high-humidity environments.
- Compactness: Small OD and thin wall configurations allow high-density tube bundles within limited chassis dimensions.
5.2 Additional Application Domains
- Industrial Heat Exchangers: Shell-and-tube heat exchangers, plate-fin compact exchangers, and vaporizers/condensers in chemical processing.
- Food & Beverage Industry: Sanitary-grade tubing for pasteurization, brewing, and dairy processing systems (EP finish, 316L grade).
- Pharmaceutical Equipment: Clean-in-place (CIP) compatible tubing for bioreactors, distillation columns, and sterile fluid transfer.
- Automotive & Aerospace: Fuel lines, brake lines, and hydraulic circuits requiring high-temperature and corrosion resistance.
- Geothermal & Solar Thermal: Heat collector tubes in closed-loop geothermal and concentrated solar thermal (CSP) systems.
- Medical Equipment: Endoscope channels, dialysis machine fluid paths, and sterilizer manifolds.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Description |
|---|---|
| ASTM A554 / A554M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Electric Resistance Welded (ERW) Tubing and Pipe |
| ASTM A269 / A269M | Standard Specification for Seamless, Cold-Worked Austenitic Stainless Steel Tubing |
| GB/T 12771 | Chinese National Standard — Stainless Steel Tubes for General Purposes |
| GB/T 14976 | Chinese National Standard — Cold-Drawn or Cold-Rolled Stainless Steel Tubes for Fluid Transport |
| EN 10216-5 | European Standard — Seamless and Welded Stainless Steel Tubes for General Purposes |
| ISO 6508 | International Standard — Tolerance for Steel Tubes |
| JIS G3446 | Japanese Industrial Standard — Stainless Steel Tubes for General Purposes |
| ASME B31.3 | Process Piping Code — Pressure Design and Material Selection |
6.2 Quality Management Certifications
- ISO 9001:2015 — Quality Management System certification covering the full manufacturing and supply chain process.
- ISO 14001:2015 — Environmental Management System certification ensuring sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System.
- CE Marking — Conformity with European directives for pressure equipment (PED 2014/68/EU) where applicable.
- TÜV / SGS Inspection — Third-party inspection and testing for export orders.
6.3 Traceability
Every coil is accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1, providing full traceability from the original steel mill heat number through all manufacturing stages. Each coil is marked with a unique serial number, material grade, dimensions, and production date for complete supply chain traceability.
7. Ordering Information
Custom configurations are available upon request, including special diameters, wall thicknesses, coil diameters, surface finishes, and end-forming operations. Wenzhou Jixing Metal Materials Co., Ltd provides technical consultation for fan coil unit coil selection, including thermal performance modeling, pressure drop calculations, and material grade recommendation based on operating conditions (fluid type, temperature range, pressure, and environment).
Technical Note: When selecting coil tube for fan coil unit applications, engineers should consider the balance between thermal conductivity (favoring 304 grade) and corrosion resistance (favoring 316 grade) based on the specific heat transfer fluid and ambient conditions. For glycol-water mixtures above 50% concentration, 316 or 316L grade is strongly recommended to prevent pitting corrosion at the weld seam.