Stainless Steel Coil Tube (Coiltube) — Product No. 982
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), catalogued as Product No. 982 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous-length tubular product supplied in coil form. This configuration enables high-throughput downstream processing, including automated bending, forming, and fabrication without the need for joint welding or seam joining that would compromise structural integrity. The coil tube is manufactured from austenitic and duplex stainless steel grades, specifically selected for superior corrosion resistance, mechanical strength, and thermal stability across a broad temperature range.
The coil tube format is particularly advantageous for applications demanding seamless, continuous tubing — such as heat exchanger coils, HVAC (Heating, Ventilation, and Air Conditioning) systems, refrigeration circuits, chemical processing lines, and hygienic fluid transfer systems. The continuous coil geometry eliminates inter-tube weld points, thereby minimizing potential failure sites and ensuring uniform hydraulic performance throughout the entire length.
2. Material Composition & Properties
2.1 Available Grades
- AISI 304 / SUS 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- AISI 316 / SUS 316 (UNS S31600) — Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion in chloride-containing environments.
- AISI 316L / SUS 316L (UNS S31603) — Low-carbon variant of 316, suitable for welded assemblies requiring resistance to sensitization and intergranular corrosion.
- AISI 321 / SUS 321 (UNS S32100) — Titanium-stabilized austenitic grade with enhanced resistance to intergranular corrosion at elevated temperatures (450–850 °C).
- AISI 304L / SUS 304L (UNS S30403) — Low-carbon version of 304 for improved weldability and post-weld corrosion resistance.
- Duplex 2205 / UNS S31803 — High-strength duplex phase stainless steel with combined ferritic-austenitic microstructure, offering 2× the yield strength of conventional 304/316 grades.
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property |
AISI 304 / 304L |
AISI 316 / 316L |
AISI 321 |
Duplex 2205 |
| Tensile Strength (Rm) [MPa] |
≥ 520 |
≥ 520 |
≥ 515 |
≥ 620 |
| Yield Strength (Rp0.2) [MPa] |
≥ 205 |
≥ 205 |
≥ 205 |
≥ 450 |
| Elongation (A50) [%] |
≥ 40 |
≥ 40 |
≥ 35 |
≥ 25 |
| Density [kg/m³] |
7930 |
8000 |
7930 |
7810 |
| Thermal Conductivity (20 °C) [W/(m·K)] |
16.3 |
16.3 |
16.3 |
14.2 |
| Maximum Service Temperature [°C] |
870 |
870 |
900 |
350 (continuous) |
2.3 Chemical Composition (Typical, wt%)
| Grade |
C [%] |
Si [%] |
Mn [%] |
P [%] |
S [%] |
Cr [%] |
Ni [%] |
Mo [%] |
Ti [%] |
N [%] |
| 304 |
≤ 0.08 |
≤ 1.00 |
≤ 2.00 |
≤ 0.045 |
≤ 0.030 |
18.0–20.0 |
8.0–10.5 |
— |
— |
— |
| 316 |
≤ 0.08 |
≤ 1.00 |
≤ 2.00 |
≤ 0.045 |
≤ 0.030 |
16.0–18.0 |
10.0–14.0 |
2.0–3.0 |
— |
— |
| 321 |
≤ 0.08 |
≤ 1.00 |
≤ 2.00 |
≤ 0.045 |
≤ 0.030 |
17.0–19.0 |
9.0–12.0 |
— |
5×(C−0.02) to 0.70 |
— |
| 2205 |
≤ 0.030 |
≤ 1.00 |
≤ 2.00 |
≤ 0.030 |
≤ 0.020 |
22.0–23.0 |
4.5–6.5 |
2.5–3.5 |
— |
0.14–0.20 |
3. Dimensions & Specifications
3.1 Outer Diameter & Wall Thickness Ranges
| Parameter |
Specification |
Standard Reference |
| Outer Diameter (OD) Range |
Φ 3.0 mm – Φ 219.1 mm |
ASTM A554, EN 10217-7 |
| Wall Thickness Range |
0.25 mm – 6.35 mm |
ASTM A554, EN 10217-7 |
| OD Tolerance (≤ Φ 25 mm) |
± 0.10 mm |
— |
| OD Tolerance (> Φ 25 mm) |
± 0.15 mm |
— |
| Wall Thickness Tolerance |
± 10% of nominal |
— |
| Coil Inner Diameter (ID) |
Φ 300 mm / Φ 400 mm / Φ 500 mm (custom available) |
— |
| Coil Length per Spool |
50 m – 500 m (depending on OD and wall thickness) |
— |
| Coil Weight |
Up to 2,000 kg per coil |
— |
3.2 Surface Finish Options
- 2B Finish — Cold-rolled, annealed, pickled, and lightly polished; matte appearance suitable for general industrial applications.
- No. 4 Brushed Finish — Uniform unidirectional grain; decorative and functional surface for visible installations.
- Mirror Polish (8K) — Electropolished or mechanically polished to Ra ≤ 0.1 μm; used in pharmaceutical and food-grade applications.
- Pickled & Passivated — Acid pickling followed by passivation treatment to restore full chromium oxide passive layer; essential for maximum corrosion resistance.
- Electropolished (EP) — Electrochemical polishing achieving Ra ≤ 0.05 μm with enhanced corrosion resistance and hygienic surface characteristics.
3.3 Delivery Condition
- Annealed (Solution Annealed / Solution Treated)
- Half-Hard (½H)
- Full-Hard (H)
4. Manufacturing Process
4.1 Process Flow
- Strip Preparation: Cold-rolled stainless steel strip (band) is sourced from certified mills and inspected for surface quality, dimensional accuracy, and chemical composition compliance.
- Forming: The strip is fed through a multi-stand roll forming line where progressive rollers shape the flat strip into a tubular profile. The forming process is carefully calibrated to minimize work-hardening and surface defects.
- Welding: The formed tube is longitudinally welded using one of the following methods:
- High-Frequency Induction Welding (HF) — Rapid heating via electromagnetic induction achieves fusion welding with minimal heat-affected zone (HAZ), preserving metallurgical properties.
- Gas Tungsten Arc Welding (GTAW / TIG) — Shielded-arc welding under inert gas (argon or helium) atmosphere, producing high-quality welds with excellent visual appearance.
- Plasma Arc Welding (PAW) — Concentrated plasma arc for precise, deep-penetration welds on thicker-wall tubing.
- Weld Heat Treatment: Post-weld solution annealing at 1050–1150 °C in a protective atmosphere (endothermic gas, hydrogen, or vacuum) dissolves chromium carbides (Cr₂₃C₆) that may have precipitated during welding, restoring full corrosion resistance.
- Coiling: The continuous tube is wound onto a coil former to produce the final coil tube product. Tension control systems ensure uniform coil layers without kinking or deformation.
- Pickling & Passivation: The welded coil undergoes chemical pickling (mixed acid bath: HNO₃/HF) to remove scale and discoloration, followed by passivation to re-establish the protective chromium oxide film (Cr₂O₃).
- Quality Inspection: Final dimensional verification, surface inspection, and non-destructive testing (NDT) prior to packaging and dispatch.
4.2 Key Process Parameters
| Process Step |
Parameter |
Typical Value |
| HF Induction Welding |
Welding Frequency |
400–800 kHz |
| HF Induction Welding |
Welding Power |
15–45 kW |
| HF Induction Welding |
Production Speed |
10–60 m/min (depending on OD and wall thickness) |
| Solution Annealing |
Temperature |
1050–1150 °C |
| Solution Annealing |
Dwell Time |
1–3 hours |
| Solution Annealing |
Atmosphere |
Endothermic gas / H₂ / Vacuum (10⁻² Pa) |
| Pickling |
Bath Composition |
HNO₃ 30–50% + HF 5–15% (by vol.) |
| Pickling |
Temperature |
40–60 °C |
5. Applications
5.1 HVAC & Refrigeration Systems
Coil tubes are