Stainless Steel Coil Tube (盘管 / Coiltube) — Technical Specification
Product Code: 1616 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Category: Stainless Steel Pipe Products
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) is a continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Unlike conventional straight-length seamless or welded stainless steel pipes, coil tubes are produced in a helical or spiral coiled configuration, enabling uninterrupted material flow through downstream processing equipment such as cold drawing benches, forming machines, and bending stations without the need for butt-welding joints between individual pipe lengths.
Coil tubes are particularly valued in high-throughput manufacturing environments where the elimination of butt joints significantly reduces cycle time, minimizes potential leak points, and enhances the structural integrity of the final fabricated product. The coiled form factor also facilitates efficient storage, transportation, and uncoiling operations, making it a preferred feedstock for precision tube processing lines.
Key Distinction: A coil tube is distinguished from a straight pipe primarily by its delivery form — the tube is wound onto a coil mandrel or spool, maintaining a continuous, joint-free length that can extend from several hundred meters to over a thousand meters per coil.
2. Material Composition & Properties
2.1 Common Grades
Coil tubes produced by Wenzhou Jixing Metal Materials Co., Ltd. are available in a range of austenitic, duplex, and ferritic stainless steel grades, with the following being the most frequently specified:
- 304 (UNS S30400 / 1.4301): General-purpose austenitic stainless steel with excellent corrosion resistance, formability, and weldability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- 304L (UNS S30403 / 1.4307): Low-carbon variant of 304 (C ≤ 0.03%) offering superior resistance to intergranular corrosion after welding. Ideal for applications involving post-weld sensitization risks.
- 316 (UNS S31600 / 1.4401): Molybdenum-bearing austenitic stainless steel (2–3% Mo) providing enhanced resistance to pitting and crevice corrosion, particularly in chloride-containing environments.
- 316L (UNS S31603 / 1.4404): Low-carbon version of 316 with improved weldability and resistance to sensitization.
- 321 (UNS S32100 / 1.4541): Titanium-stabilized austenitic grade offering excellent resistance to intergranular corrosion at elevated temperatures.
- 310S (UNS S31008 / 1.4845): High-temperature austenitic grade with outstanding oxidation resistance up to 1150°C (2094°F).
- Duplex 2205 (UNS S32205 / 1.4462): 22% Cr, 5% Ni, 3% Mo duplex stainless steel with approximately double the yield strength of standard austenitic grades and superior resistance to chloride stress corrosion cracking (SCC).
- 430 (UNS S43000 / 1.4006): Ferritic stainless steel offering good resistance to atmospheric and mild chemical corrosion at a lower cost than austenitic grades.
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property | 304 / 304L | 316 / 316L | Duplex 2205 |
|---|---|---|---|
| Tensile Strength (UTS), MPa | ≥ 515 | ≥ 515 | ≥ 550 |
| Yield Strength (0.2% offset), MPa | ≥ 205 | ≥ 205 | ≥ 450 |
| Elongation (A₅), % | ≥ 40 | ≥ 40 | ≥ 25 |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 310 |
| Density, g/cm³ | 8.00 | 8.03 | 7.85 |
| Thermal Expansion (20–100°C), ×10⁻⁶/K | 17.3 | 16.0 | 12.7 |
| Maximum Service Temperature, °C | 870 | 870 | 350 |
2.3 Corrosion Resistance
The corrosion performance of coil tubes is governed primarily by the Passive Film (钝化膜) formed by the Chromium (Cr) content on the steel surface. Grades containing Molybdenum (Mo) — such as 316L and 2205 — exhibit significantly higher Pitting Resistance Equivalent Number (PREN), calculated as:
PREN = %Cr + 3.3 × %Mo + 16 × %N
- 304/304L: PREN ≈ 19
- 316/316L: PREN ≈ 24–26
- Duplex 2205: PREN ≈ 35
3. Product Specifications
3.1 Dimensional Range
| Parameter | Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD), mm | 6.0 – 219.0 | ASTM A554 / A213 / GB/T 12771 |
| Wall Thickness (WT), mm | 0.5 – 6.0 | ASTM A554 / EN 10216-5 |
| Coil Length per Spool, m | 50 – 1,000+ | Manufacturer specification |
| Coil Inner Diameter (ID), mm | 200 – 600 | Customizable |
| Flatness / Roundness Tolerance | ±0.5% of OD | ASTM A554 |
| Weld Seam Height (if applicable) | ≤ 10% of WT | ASTM A554 |
3.2 Surface Finish Options
- 2B (Cold Rolled & Annealed): Standard mill finish with a matte, slightly reflective appearance. Suitable for general industrial applications.
- No. 4 Brushed: Uniform directional grain finish providing an attractive aesthetic appearance while maintaining corrosion resistance.
- Mirror / 8K: High-polish finish achieving a reflectivity of ≥ 90%. Used in architectural and decorative applications.
- Pickled & Passivated: Chemically cleaned surface free of scale and oxide contamination, with an enhanced passive film for maximum corrosion protection.
3.3 Applicable Standards
| Standard | Description |
|---|---|
| ASTM A554 | Standard Specification for Cold-Worked Austenitic Stainless Steel Tubular Products (Seamless and Welded) in Coil or Straight Lengths |
| ASTM A213 | Standard Specification for Seamless Ferritic and Austenitic Cr–Ni Stainless Steel Tubing for High-Temperature Service |
| EN 10216-5 | Steel Tubes for Pressure Purposes — Technical Delivery Conditions — Part 5: Non-Heat-Resistant Stainless Steel Tubes |
| GB/T 12771 | Stainless Steel Seamless Tubes for General Purposes (Chinese National Standard) |
| GB/T 14976 | Stainless Steel Seamless Tubes for Fluid Transport (Chinese National Standard) |
| ISO 11836 | Stainless Steel Tubes for Pressure Purposes — Technical Delivery Conditions |
| JIS G3459 | Seamless Stainless Steel Tubes for General Use (Japanese Industrial Standard) |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage process that ensures dimensional accuracy, metallurgical integrity, and surface quality. The following describes the complete manufacturing workflow:
4.1 Raw Material Preparation
Hot-rolled stainless steel strip or skelp (窄带/扁钢) is sourced from certified steel mills. Incoming material undergoes rigorous chemical composition verification via Optical Emission Spectroscopy (OES, 光谱分析) and physical property testing to confirm compliance with the specified grade requirements.
4.2 Forming (Tube Milling)
The flat strip is fed through a series of progressively reducing rollers in a Tube Mill (制管机) to form the desired tubular cross-section. For round tubes, the mill progressively rounds the flat profile. The forming process is closely controlled to maintain dimensional tolerances and prevent material thinning or wrinkling.
4.3 Welding (for Welded Coil Tubes)
In the case of welded coil tubes, the formed strip edges are fused using one of the following methods:
- TIG (Tungsten Inert Gas) Welding: Provides high-quality, aesthetically superior weld seams with minimal heat-affected zone. Preferred for thin-wall applications.
- IGBT-Pulse MIG (Metal Inert Gas) Welding: High-speed welding process suitable for thicker wall sections, utilizing a pulsed arc for precise heat input control.
- Friction Stir Welding (FSW, 搅拌摩擦焊): A solid-state welding technique that eliminates melting and associated metallurgical concerns, producing welds with mechanical properties approaching the base metal.
Nitrogen Back-Purging (氮背保护): During the welding process, high-purity Nitrogen (N₂, ≥ 99.995%) is introduced into the tube interior — a process known as Nitrogen Back-Purging (注氮工艺). This inert atmosphere prevents internal oxidation of the weld zone, thereby maintaining the full corrosion resistance of the internal surface. The nitrogen injection process is critical for ensuring that the weld seam does not become a preferential site for corrosion initiation, particularly in aggressive chemical environments. Proper nitrogen flow rates (typically 0.5–2.0 L/min per inch of tube diameter) and oxygen level monitoring (target: O₂ ≤ 50 ppm in the weld zone) are essential for quality assurance.
4.4 Heat Treatment
Following welding and forming, the coil tube undergoes Solution Annealing (固溶退火) at temperatures typically between 1050°C and 1150°C, followed by rapid water quenching. This process:
- Dissolves carbide precipitates (e.g., Cr₂₃C₆) that may have formed during welding, restoring full Chromium availability for the passive film.
- Relieves residual stresses introduced during cold forming and welding.
- Uniformizes the microstructure, ensuring consistent mechanical properties throughout the tube.
4.5 Cold Working (Optional)
For applications requiring higher strength or tighter dimensional tolerances, the coil tube may undergo Cold Drawing (冷拔) or Cold Rolling (冷轧). This process increases tensile strength by 20–40% through work hardening while reducing wall thickness and improving roundness. The degree of cold reduction is carefully controlled to avoid excessive strain hardening that could compromise ductility.
4.6 Surface Treatment
The final surface preparation includes:
- Pickling (酸洗): Removal of mill scale and oxide films using a mixed acid solution (typically HNO₃ + HF or H₂SO₄ + HNO₃).
- Passivation (钝化): Chemical treatment using dilute Nitric Acid (HNO₃) or Citric Acid (柠檬酸) to enrich the surface Chromium content and establish a robust, stable passive film (Cr₂O₃).
- Polishing / Brushing: Mechanical finishing to achieve the specified surface finish grade.
4.7 Coiling & Packaging
The finished tube is wound onto a coil spool at controlled tension to prevent deformation, kinking, or surface marring. Each coil is protected with waterproof paper wrapping, VCI (Vapor Corrosion Inhibitor, 气相缓蚀剂) film, and steel strapping. Coils are secured on wooden pallets or steel stands for safe transport.
5. Applications
The continuous, joint-free nature of coil tubes makes them indispensable across a wide spectrum of industrial and commercial applications:
5.1 Precision Tube Processing
- Cold Drawing Feeds: Coil tubes serve as the primary feedstock for cold drawing benches (冷拔生产线), where they are pulled through dies to achieve ultra-tight dimensional tolerances (±0.1 mm or better) for applications in hydropneumatic cylinders, medical devices