Stainless Steel Coil Tube — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, continuous-length tubular product supplied in coiled form. Unlike traditional straight-length seamless or welded tubes, coil tubes are produced in a continuous helical configuration, enabling downstream processing without the need for cutting, welding, or re-fixturing — thereby significantly reducing material waste, labor costs, and production cycle time. This product is particularly suited for high-volume, high-precision manufacturing applications including HVAC (Heating, Ventilation, and Air Conditioning) fan coil units, heat exchangers, refrigeration systems, automotive radiators, and process piping.
The coil tube product line encompasses both seamless coil tubes (produced via cold drawing or rotary piercing) and welded coil tubes (produced via ERW — Electric Resistance Welding, or TIG — Tungsten Inert Gas welding), with outer diameters ranging from 3 mm to 159 mm and wall thicknesses from 0.3 mm to 8 mm.
2. Material & Properties
2.1 Available Grades
- 304 / 304L (UNS S30400 / S30403) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- 316 / 316L (UNS S31600 / S31603) — Enhanced molybdenum content for superior resistance to chlorides and pitting corrosion
- 321 (UNS S32100) — Titanium-stabilized grade suitable for high-temperature service up to 870 °C
- 316Ti (UNS S31635) — Titanium-stabilized 316 variant for welding and high-temperature applications
- 904L (UNS N08904) — High-alloy austenitic grade for extreme corrosion environments
- 2205 Duplex (UNS S31803) — High-strength duplex stainless steel with outstanding resistance to chloride stress corrosion cracking (CSCC)
2.2 Mechanical Properties (Annealed Condition, Representative)
| Grade | Tensile Strength (Rm, MPa) |
Yield Strength (Rp0.2, MPa) |
Elongation (A, %) |
Hardness (HV) |
Service Temperature Range |
|---|---|---|---|---|---|
| 304 / 304L | ≥ 520 | ≥ 205 | ≥ 40 | ≤ 200 | −196 °C to 870 °C |
| 316 / 316L | ≥ 515 | ≥ 170 | ≥ 40 | ≤ 200 | −196 °C to 870 °C |
| 321 | ≥ 515 | ≥ 205 | ≥ 40 | ≤ 200 | −196 °C to 870 °C |
| 904L | ≥ 600 | ≥ 220 | ≥ 35 | ≤ 220 | −196 °C to 1000 °C |
| 2205 Duplex | ≥ 450 | ≥ 220 | ≥ 25 | ≤ 310 | −50 °C to 250 °C |
2.3 Chemical Composition Requirements (wt%)
| Grade | C | Cr | Ni | Mo | Ti | N |
|---|---|---|---|---|---|---|
| 304 | ≤ 0.08 | 18.0–20.0 | 8.0–10.5 | — | — | — |
| 304L | ≤ 0.03 | 18.0–20.0 | 8.0–10.5 | — | — | — |
| 316 | ≤ 0.08 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — | — |
| 316L | ≤ 0.03 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — | — |
| 321 | ≤ 0.08 | 17.0–19.0 | 9.0–12.0 | — | 5 × C – 0.40 to 0.70 | — |
| 904L | ≤ 0.020 | 19.0–23.0 | 23.0–25.0 | 4.0–5.0 | — | ≤ 0.20 |
| 2205 | ≤ 0.030 | 22.0–23.0 | 4.5–6.5 | 3.0–3.5 | — | 0.14–0.20 |
2.4 Key Material Advantages
- Corrosion Resistance: The passive chromium oxide (Cr₂O₃) film formed on the surface provides exceptional resistance to atmospheric, chemical, and marine corrosion environments. 316/316L grades offer superior pitting and crevice corrosion resistance due to the presence of molybdenum (Mo).
- Hygienic Surface Quality: Available in No. 4 brushed, BA (Bright Annealed), and mirror (8K) finishes with surface roughness (Ra) values as low as 0.2 μm, suitable for pharmaceutical, food-grade, and semiconductor applications.
- Weldability: Low-carbon "L" grades (304L, 316L) minimize intergranular corrosion (IGC) risk during welding, ensuring long-term structural integrity in welded assemblies.
- Temperature Stability: Austenitic grades maintain ductility and toughness across an exceptionally wide temperature range, including cryogenic service at −196 °C (liquid nitrogen temperature).
- Magnetic Properties: 304/316 grades are essentially non-magnetic in the annealed condition (≤ 5 μm permeability deviation), which is critical for electronic and medical equipment applications.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Range / Value | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3 mm – 159 mm | ASTM A269, EN 10216-5, GB/T 12771 |
| Wall Thickness (WT) | 0.3 mm – 8.0 mm | — |
| Coil Length (per coil) | 50 m – 500 m (customizable) | — |
| Coil Inner Diameter (ID) | 300 mm / 500 mm / 600 mm | — |
| OD Tolerance | ±0.10 mm (≤ 10 mm OD); ±0.15 mm (> 10 mm OD) | ASTM A269 |
| WT Tolerance | ±10% of nominal (min. ±0.05 mm) | ASTM A269 |
| Flatness / Ovality | ≤ 0.5% of OD | — |
| Surface Roughness (Ra) | 0.2 – 1.6 μm (depending on finish) | ASTM A270 |
3.2 Surface Finish Options
| Finish Type | Description | Typical Ra (μm) | Application |
|---|---|---|---|
| BA (Bright Annealed) | Protective annealing in controlled atmosphere; smooth, reflective surface | 0.4 – 0.8 | Food processing, pharmaceutical, decorative |
| No. 4 Brushed | Unidirectional grain pattern via abrasive brushing | 0.8 – 1.6 | Architectural, HVAC, general industrial |
| Mirror (8K) | Multi-stage polishing to specular reflectivity | 0.2 – 0.4 | Decorative, optical, high-end appliances |
| Pickled & Passivated | Acid pickling followed by passivation treatment | 0.8 – 1.6 | Welded assemblies, chemical processing |
| Electropolished | Electrochemical polishing for ultra-smooth surface | 0.1 – 0.2 | Semiconductor, biotech, ultra-pure fluid systems |
3.3 Available Standards & Specifications
- ASTM A269 — Specification for Seamless and Welded Austenitic Stainless Steel Pipes and Tubes
- ASTM A270 — Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing
- ASTM B138 — Specification for Seamless Ferritic and Austenitic Chromium Stainless Steel Tubing
- EN 10216-5 — Non-alloy and alloy steel tubes for pressure purposes — Part 5: Technical delivery conditions for austenitic stainless steel tubes
- GB/T 12771 — Chinese national standard for stainless steel seamless tubes
- JIS G3447 / G3459 — Japanese Industrial Standards for austenitic stainless steel tubes
- ASME SA-213 / SA-269 — Boiler and Pressure Vessel Code material specifications
4. Manufacturing Process
4.1 Seamless Coil Tube Production
- Hot Rolling (Hollowing): Steel billets are heated to 1,150–1,200 °C and pierced on a rotary piercing mill to form a hollow shell (blanks). The piercing ratio (ID of blank to billet diameter) is controlled to minimize surface defects and ensure uniform wall thickness.
- Hot Reduction: The hollow shell is passed through a series of hot reduction stands (typically 6–12 stands) to reduce the OD and wall thickness to near-final dimensions. Intermediate reheating may be performed between passes.
- Coil Winding: The hot-rolled tube is wound onto a coil reel while still above the recrystallization temperature (approximately 600 °C for 304 grade), ensuring a stress-free, uniform microstructure.
- Solution Annealing & Pickling: The coil is heat-treated at 1,050–1,150 °C in a protective atmosphere (endothermic gas or vacuum), followed by rapid water quenching to dissolve carbides and restore full corrosion resistance. The coil is then acid-pickled (HNO₃ + HF mixture) to remove scale and passivated to form a stable chromium oxide film.
- Cold Drawing / Cold Rolling (Optional): For tighter tolerances and improved mechanical properties, the coil is passed through cold-drawing dies or cold-rolling mills. This reduces OD by 5–30% and increases yield strength by 30–100% while improving surface finish.
- Final Annealing: A stress-relief annealing at 900–1,100 °C eliminates work-hardening and restores ductility for downstream forming operations.
- Surface Finishing: BA treatment, polishing, or electropolishing is applied according to the customer's specification.
- Quality Inspection & Packaging: Each coil undergoes 100% visual inspection, dimensional verification, hydrostatic testing (as required), and material certification before packaging in moisture-proof wrapping with protective end caps.
4.2 Welded Coil Tube Production
- Steel Strip Preparation: Cold-rolled stainless steel strip (SLIT from coil) is slit to the required width and inspected for surface quality.
- Edge Beveling: Strip edges are beveled to ensure proper weld formation.
- Forming (Rolling): The flat strip is passed through a series of forming rolls to create the desired cross-sectional shape (round, oval, rectangular, etc.).