Stainless Steel Coil Tube — Model No. 713 (Coiltube Series)
1. Product Overview
The Stainless Steel Coil Tube (Coiltube Series, Model No. 713) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed in a continuous coiled configuration, offering superior flexibility, ease of handling, and efficient material utilization compared to straight-length tubing. The coil tube is primarily fabricated from austenitic stainless steel grades, providing exceptional corrosion resistance, mechanical integrity, and thermal stability across a wide range of industrial and commercial applications.
The coiled form factor is particularly advantageous for applications involving heat exchangers, HVAC (Heating, Ventilation, and Air Conditioning) systems, and fluid transport networks where serpentine routing, compact installation, and thermal expansion accommodation are critical design considerations. This product line has been extensively evaluated in performance comparisons between improved all-air induction units and fan coil units, demonstrating reliable thermal-hydraulic performance under sustained operational conditions.
2. Material and Properties
2.1 Material Grades
The Coiltube Series is manufactured using the following primary stainless steel grades:
- AISI 304 (UNS S30400) — General-purpose austenitic stainless steel with balanced corrosion resistance and formability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316 (UNS S31600) — Enhanced corrosion resistance grade with 2–3% Molybdenum (Mo) addition, suitable for chloride-containing environments and aggressive chemical applications.
- AISI 321 (UNS S32100) — Stabilized grade with Titanium (Ti) addition, providing improved resistance to intergranular corrosion at elevated temperatures (450–850°C).
2.2 Mechanical Properties (AISI 304, Annealed Condition)
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75,000 psi) | ASTM A312 / ASTM E8 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,700 psi) | ASTM A312 / ASTM E8 |
| Elongation (at Break) | ≥ 40% | ASTM A312 / ASTM E8 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM E140 |
| Density | 8.0 g/cm³ | — |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | ASTM E1461 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
2.3 Chemical Composition (AISI 304, wt%)
| Element | Specification |
|---|---|
| Carbon (C) | ≤ 0.08% |
| Chromium (Cr) | 18.0 – 20.0% |
| Nickel (Ni) | 8.0 – 10.5% |
| Manganese (Mn) | ≤ 2.0% |
| Silicon (Si) | ≤ 0.75% |
| Phosphorus (P) | ≤ 0.045% |
| Sulfur (S) | ≤ 0.030% |
| Iron (Fe) | Balance |
2.4 Surface Finish Options
- 2B (Cold Rolled and Annealed) — Matte finish, suitable for general industrial applications
- No. 4 Brushed Finish — Directional satin finish with uniform grain pattern
- Mirror Polish (8K) — High-gloss reflective surface, Ra ≤ 0.05 μm
- Pickled and Passivated (PP) — Chemical surface treatment for enhanced corrosion resistance
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Model | No. 713 Coiltube Series |
| Outer Diameter (OD) | Φ6.0 mm – Φ50.8 mm (¼" – 2") |
| Wall Thickness | 0.5 mm – 3.0 mm (0.020" – 0.118") |
| Coil Inner Diameter (CID) | Φ300 mm – Φ600 mm (12" – 24") |
| Coil Length per Spool | 50 m – 500 m (configurable) |
| Dimensional Tolerance (OD) | ± 0.05 mm (± 0.002") |
| Dimensional Tolerance (Wall Thickness) | ± 10% of nominal |
| Roundness | ≤ 0.5% of OD |
| Straightness (per meter) | ≤ 1.0 mm/m |
| Operating Temperature Range | -196°C to +870°C (AISI 304) |
| Maximum Working Pressure (Φ12.7 mm × 1.5 mm) | ≈ 12.5 MPa (1,813 psi) |
| Standard Reference | ASTM A312 / ASTM A269 / EN 10217-7 |
| Coil Packaging | Wooden pallet with moisture-proof wrapping |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection — Incoming stainless steel strip is verified for chemical composition (via Optical Emission Spectroscopy, OES) and mechanical properties in accordance with ASTM A240 specifications.
- Slitting and Leveling — Cold-rolled coil is slit to target width and passed through a leveling mill to ensure uniform flatness and residual stress relief.
- Forming (Roll Forming / Seamless) — The strip is formed into tubular geometry using either high-precision roll forming dies or seamless piercing methods, depending on diameter and wall thickness requirements.
- Welding (where applicable) — For welded coil tube, high-frequency induction welding (HF welding) or automatic Argon Arc Welding (TIG) is employed to produce a consistent, leak-tight weld seam.
- Heat Treatment (Solution Annealing) — The formed tube undergoes solution annealing at 1050–1150°C in a protective atmosphere (argon or vacuum), followed by rapid cooling, to restore full austenitic microstructure and eliminate residual stresses.
- Pickling and Passivation — The tube is immersed in a mixed acid bath (HNO₃ + HF) to remove oxide scale, followed by passivation treatment to form a protective chromium oxide layer.
- Coiling — The finished tube is wound onto a precision coiling stand at controlled tension to maintain dimensional accuracy and prevent kinking or deformation.
- Final Inspection and Packaging — Each coil is subjected to dimensional verification, visual inspection, and hydrostatic pressure testing before being packaged for shipment.
4.2 Microstructural Characteristics
The final microstructure of the annealed Coiltube Series consists of a fully austenitic (face-centered cubic, FCC) grain structure with grain size typically in the range of 60–150 μm (ASTM Grain Size 5–8). This microstructure ensures excellent ductility, isotropic mechanical properties, and non-magnetic characteristics (magnetic permeability ≤ 1.05 relative permeability in the annealed condition).
5. Applications
5.1 HVAC and Thermal Management Systems
The Coiltube Series has been specifically evaluated in the context of improved all-air induction units and fan coil units (FCUs). In these applications, the stainless steel coil tube serves as the refrigerant or hot water heat transfer element within the coil assembly. Key performance advantages include:
- Superior thermal conductivity relative to carbon steel alternatives in corrosive condensate environments
- Resistance to acidification of condensate water (pH 4.5–6.0) common in HVAC systems
- Compact serpentine routing enabled by the coiled form, maximizing heat transfer area within constrained installation spaces
- Elimination of galvanic corrosion at dissimilar metal junctions when paired with aluminum fin stock
5.2 Additional Application Domains
- Food and Pharmaceutical Processing — Sanitary-grade tubing for fluid transport in CIP (Clean-In-Place) systems
- Chemical Processing — Corrosion-resistant piping for aggressive chemical media
- Automotive Industry — Exhaust system components, fuel lines, and heat exchanger elements
- Building Construction — Gas and water supply lines, structural bracing
- Medical Equipment — Instrument tubing and sterilizable fluid lines
- Marine and Offshore — Seawater cooling circuits and ballast systems
6. Quality Certifications and Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System certification |
| ASTM A312 | Standard Specification for Seamless, Welded, and Heavy-Walled Stainless Steel Pipe, Tube, and Fittings |
| ASTM A269 | Standard Specification for Seamless and Wrought Stainless Steel Tubing for Chemical and Similar Severe Service |
| EN 10217-7 | European standard for stainless steel tubes for pressure purposes — General technical delivery conditions |
| GB/T 12771 | Chinese National Standard for stainless steel seamless tubes for fluid transport |
| 3.1 / 3.2 Material Certificates | EN 10204 compliant material test certificates with full traceability |
| Hydrostatic Test | 100% pressure testing at 1.5× maximum working pressure |
| Eddy Current Testing | Non-destructive testing (NDT) for weld seam integrity verification |
7. Unique Selling Points
The Coiltube Series (Model No. 713) from Wenzhou Jixing Metal Materials Co., Ltd distinguishes itself through the following value propositions:
- Continuous Coil Configuration — Eliminates field welding requirements, reduces installation time by up to 60%, and minimizes leak points in critical fluid systems.
- Proven HVAC Performance — Validated through comparative performance testing of all-air induction units versus fan coil units, demonstrating consistent thermal-hydraulic efficiency under sustained operating loads.
- Precision Dimensional Control — Tight tolerance manufacturing (± 0.05 mm OD) ensures reliable fit with standard fittings, brazing connections, and heat exchanger headers.
- Full Traceability — Each coil is accompanied by a comprehensive material test certificate (EN 10204 Type 3.1/3.2) with heat number traceability, chemical analysis, and mechanical test data.
- Corrosion-Free Lifespan — Austenitic stainless steel construction provides a service life exceeding 25 years in atmospheric and condensate environments, significantly outperforming carbon steel alternatives.
- Customizable Specifications — Available in multiple grades, diameters, wall thicknesses, and surface finishes to meet project-specific engineering requirements.
- Environmental Sustainability — Stainless steel is 100% recyclable, and the coil form reduces material waste during fabrication by minimizing cut-off losses.
8. Ordering Information
Customers may specify the following parameters when placing orders for the Coiltube Series:
- Material grade (AISI 304, 316, 321, or equivalent)
- Outer diameter and wall thickness (refer to specification table)
- Coil inner diameter preference
- Required coil length per spool
- Surface finish requirement (2B, No. 4, Mirror, or PP)
- Applicable standard (ASTM, EN, GB, or custom)
- Required certification level (3.1 or 3.2)
- Special inspection or testing requirements
9. Technical Advisory Note
Design Consideration: When incorporating the Coiltube Series into HVAC heat exchanger assemblies, engineers should account for the differential thermal expansion coefficient between stainless steel (17.3 × 10⁻⁶/°C) and aluminum fins (23.1 × 10⁻⁶/°C). Expansion loops or flexible connections are recommended for installations exceeding 3 meters of continuous run to prevent thermal stress accumulation. Additionally