Stainless Steel Coil Tube (Coil Tube) — Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (Coil Tube), product code 1523, is a precision-engineered continuous-length tubing solution manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is supplied in coil form to facilitate downstream processing operations such as forming, bending, welding, and cutting without the need for splicing or joint fabrication. The coil tube is specifically designed for applications requiring high flow efficiency, thermal conductivity, and long-term corrosion resistance — including HVAC (Heating, Ventilation, and Air Conditioning) systems, fan coil units (FCUs), refrigeration circuits, heat exchangers, and fluid transfer systems.
Wenzhou Jixing Metal Materials Co., Ltd. leverages advanced metallurgical expertise and state-of-the-art cold-rolling and forming technologies to deliver coil tubes that meet or exceed international standards for dimensional accuracy, surface finish, and mechanical integrity. The continuous coil configuration eliminates butt welds inherent in straight-length pipe products, thereby enhancing structural reliability and reducing leak points in critical service environments.
2. Material & Properties
2.1 Base Material Grades
The coil tube is manufactured from high-grade austenitic and duplex stainless steel alloys, including but not limited to:
- AISI 304 / EN 1.4301 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- AISI 316 / EN 1.4401 (UNS S31600) — Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion in chlorinated environments.
- AISI 316L / EN 1.4404 (UNS S31603) — Low-carbon variant of 316 suitable for welding applications where sensitization must be avoided.
- AISI 321 / EN 1.4541 (UNS S32100) — Titanium-stabilized austenitic grade for elevated-temperature service up to 870 °C.
- AISI 310S / EN 1.4845 (UNS S31008) — High-temperature austenitic grade with exceptional oxidation resistance.
- AISI 2205 Duplex (UNS S31803) — Duplex austenitic-ferritic grade offering yield strength approximately double that of 304 at equivalent corrosion resistance.
2.2 Key Mechanical Properties (Typical Values for AISI 304 Grade)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (74.7 ksi) | ASTM A213 / EN 10216-5 |
| Yield Strength (0.2% offset) | ≥ 205 MPa (29.7 ksi) | ASTM A213 / EN 10216-5 |
| Elongation (at break) | ≥ 40% | ASTM A213 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A213 |
| Density | 8.00 g/cm³ | — |
| Thermal Conductivity (20 °C) | 16.3 W/(m·K) | ASTM E153 |
| Specific Heat Capacity | 500 J/(kg·K) | — |
| Thermal Expansion Coefficient (20–100 °C) | 17.3 × 10⁻⁶ /K | — |
| Maximum Service Temperature | 870 °C (oxidation); 595 °C (mechanical) | ASME BPVC Section II |
2.3 Chemical Composition (AISI 304 — Typical)
| Element | Content (wt%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Chromium (Cr) | 18.0 – 20.0 |
| Nickel (Ni) | 8.0 – 10.5 |
| Manganese (Mn) | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Nitrogen (N) | ≤ 0.10 |
| Iron (Fe) | Balance |
2.4 Corrosion Resistance Characteristics
- Pitting Resistance (PREN): AISI 304 — PREN ≈ 19; AISI 316 — PREN ≈ 24; AISI 2205 Duplex — PREN ≈ 33–38.
- Intergranular Corrosion: Fully solution-annealed (austenitizing) treatment at 1010–1150 °C followed by rapid water quench ensures full sensitization resistance.
- Stress Corrosion Cracking (SCC): Inherent resistance in non-chloride environments; 316L and duplex grades recommended for chloride-bearing service above 60 °C.
- Crevice Corrosion: Enhanced by low-carbon (L) grades and molybdenum additions; critical crevice width thresholds significantly extended.
3. Specifications
3.1 Dimensional Parameters
| Parameter | Range / Value | Tolerance |
|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ114.3 mm | ±0.1 mm (≤ Φ25 mm); ±0.15% (＞ Φ25 mm) |
| Wall Thickness (WT) | 0.3 mm – 6.0 mm | ±10% (≤ 1.0 mm); ±0.1 mm (＞ 1.0 mm) |
| Inner Diameter (ID) | Φ2.4 mm – Φ102.3 mm | Derived from OD and WT tolerances |
| Coil Length | Up to 3,000 m (continuous) | — |
| Coil Weight | Up to 3,000 kg per coil | — |
| Coil Inner Diameter (Core) | Φ152 mm (6") / Φ203 mm (8") / Φ305 mm (12") | ±2 mm |
| Coil Outer Diameter (Max) | Φ1,000 mm | — |
| Surface Finish | 2B (Cold-rolled, Annealed, Bright), No. 1 (Annealed), BA (Bright Annealed), Mirror (Ra ≤ 0.1 μm) | Per ASTM A473 |
| End Condition | Flat cut, saw-cut, or welded joint (butt-welded coil) | — |
| Minimum Bend Radius | 3D (3× OD) cold; 1.5D with mandrel | — |
3.2 Applicable Standards
- ASTM A213 / A213M — Standard Specification for Seamless Austenitic Stainless Steel Tubes for High-temperature Service.
- ASTM A554 / A554M — Standard Specification for Heat-Resistant Stainless Steel Seamless Tubes.
- ASTM A778 — Standard Specification for Seamless Austenitic Stainless Steel Tubing for Chemical and Other Similar Services at High Temperatures.
- EN 10216-5 — Non-alloy and Alloy Steel Tubes for Mechanical and Thermal Uses — Part 5: Non-ferrous Alloy Tubes.
- EN 10217-7 — Tubes for Mechanical and Thermal Uses — Part 7: Austenitic Stainless Steel Tubes.
- ISO 13987 — Tubes for Mechanical and Thermal Uses — General Requirements.
- JIS G3459 — Seamless Stainless Steel Tubes for General Purposes.
- GB/T 13296 — Seamless Stainless Steel Tubes for General Purposes (Chinese National Standard).
- ASME SA-213 — Seamless Ferritic, Austenitic, and Ferritic-Austenitic Stainless Steel Tubes for High-temperature Service.
- ASME SA-778 — Seamless Austenitic Stainless Steel Tubing for Chemical and Other Similar Services at High Temperatures.
4. Manufacturing Process
4.1 Process Flowchart
- Raw Material Selection & Incoming Inspection: Hot-rolled stainless steel seamless tube blanks are sourced from certified mills. Incoming material undergoes 100% visual inspection, ultrasonic testing (UT), and chemical composition verification via Optical Emission Spectrometry (OES) or Inductively Coupled Plasma (ICP) analysis.
- Acid Pickling & Descaling: The tube blank is subjected to a controlled acid pickling bath (HNO₃ + HF or HNO₃ + H₂SO₄ mixture) to remove mill scale, oxide layers, and surface contaminants. This ensures a clean, active surface for subsequent cold working.
- Passivation Treatment: Following pickling, a passivation step using dilute nitric acid (HNO₃ 20–30%) or citric acid promotes the formation of a stable, adherent chromium oxide (Cr₂O₃) passive film, restoring full corrosion resistance.
- Cold Drawing / Cold Pilgering: The tube is cold-drawn through precision tungsten carbide (WC) or diamond dies to achieve the target outer diameter and wall thickness. This process imparts significant cold work hardening, enhancing mechanical strength and dimensional accuracy.
- Intermediate Annealing: When multi-pass cold drawing is required, intermediate annealing at 1050–1100 °C in a protective atmosphere (argon or nitrogen) relieves accumulated cold work, restores ductility, and prevents cracking.
- Final Dimensional Forming: The tube undergoes final sizing and roundness correction to meet tight dimensional tolerances. Laser diameter measurement systems provide real-time feedback control.
- Final Annealing & Stress Relief: A controlled austenitizing anneal at 1010–1150 °C followed by rapid quenching (water or forced air) eliminates residual stresses from cold working, ensures full solution homogenization, and achieves the desired mechanical properties and microstructure.
- Surface Finishing: Depending on the specified finish, the tube may undergo electropolishing (to achieve Ra ≤ 0.05 μm), mechanical polishing, or passivation. Surface roughness is verified by profilometry.
- Coil Winding: The finished tube is wound onto a steel core using a precision coil winding machine with tension control to prevent inter-coil contact damage, deformation, or surface marring. Protective wrapping (VCI paper, PE film, or wooden spacers) is applied between coil layers.
- Final Quality Inspection & Testing: Comprehensive final inspection includes dimensional verification (caliper, micrometer, bore gauge), hydrostatic pressure testing (per ASTM A530), visual examination, and optional non-destructive testing (eddy current, magnetic particle, or dye penetrant).
- Packaging & Dispatch: Coils are shrink-wrapped, strapped, and palletized for secure transport. Each coil is labeled with a unique traceability tag containing heat number, mill test certificate reference, dimensions, and grade designation.
4.2 Key Process Parameters
| Process Stage | Parameter | Typical Value |
|---|---|---|
| Acid Pickling | Bath Temperature | 50 – 70 °C |
| Acid Pickling | Duration | 5 – 20 minutes |
| Cold Drawing | <