Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous-length tubular product supplied in coiled configuration, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Unlike traditional straight-length stainless steel tubing, the coil tube is wound onto spools or coils during the manufacturing process, enabling seamless handling, storage, and downstream processing without the need for intermediate cutting or straightening operations. This product category is governed by international and national standards, including ASTM A269, ASTM A312, EN 10216-5, GB/T 12771, and the specific test methodology outlined in the standard "Room Temperature Tensile Test Methods for Metal Coil Tubes" (《金属盘管的室温拉伸试验方法》).
The coil tube configuration offers distinct advantages in terms of material utilization, dimensional consistency, and cost efficiency, making it a preferred choice for high-volume industrial applications where continuous tubular feed is required.
2. Material & Properties
2.1 Material Grades
The stainless steel coil tubes are available in a comprehensive range of austenitic, duplex, and ferritic grades, including but not limited to:
- Austenitic Grades: 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603), 310S (UNS S31008), 321 (UNS S32100)
- Duplex Grades: 2205 (UNS S32205), 2507 (UNS S32750)
- Ferritic Grades: 430 (UNS S43000), 446 (UNS S44600)
- Specialty Grades: 904L (UNS N08904), Alloy 20 (UNS N08200), Hastelloy C-276 (UNS N10276)
2.2 Mechanical Properties
Mechanical performance is validated through Room Temperature Tensile Testing in accordance with the standard methodology for metal coil tubes. Key mechanical characteristics include:
- Tensile Strength (UTS — Ultimate Tensile Strength): Typically 515–720 MPa for austenitic grades; up to 800 MPa for duplex grades
- Yield Strength (0.2% Proof Stress, Rp0.2): 205–450 MPa depending on grade and temper condition
- Elongation at Break (A): ≥ 30% for annealed austenitic grades; ≥ 25% for duplex grades
- Hardness: ≤ 230 HV (annealed condition), verifiable via Vickers or Rockwell B scale
2.3 Chemical Composition (Representative — Grade 316L)
| Element | Specification (wt%) |
|---|---|
| C (Carbon) | ≤ 0.030 |
| Si (Silicon) | ≤ 1.00 |
| Mn (Manganese) | ≤ 2.00 |
| P (Phosphorus) | ≤ 0.045 |
| S (Sulfur) | ≤ 0.030 |
| Cr (Chromium) | 16.00 – 18.00 |
| Ni (Nickel) | 10.00 – 14.00 |
| Mo (Molybdenum) | 2.00 – 3.00 |
| N (Nitrogen) | ≤ 0.10 |
| Fe (Iron) | Balance |
2.4 Physical Properties
- Density: 7.93 g/cm³ (austenitic grades)
- Thermal Conductivity: 16.3 W/(m·K) at 100°C
- Thermal Expansion Coefficient: 16.0–18.0 × 10⁻⁶ /K (20–100°C)
- Electrical Resistivity: 0.72 μΩ·m (20°C)
- Maximum Service Temperature: Up to 870°C (304), 925°C (310S)
3. Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.00 mm – 159.00 mm | ASTM A269 / EN 10216-5 |
| Wall Thickness (WT) | 0.50 mm – 12.00 mm | ASTM A269 / GB/T 12771 |
| Coil Length | 50 m – 300 m per coil (continuous) | Manufacturer Specification |
| Coil Inner Diameter | 300 mm – 600 mm | Manufacturer Specification |
| OD Tolerance | ± 0.10 mm to ± 0.50 mm (per size) | ASTM A269 / EN 10216-5 |
| Wall Thickness Tolerance | ± 10% of nominal | ASTM A269 |
| Surface Finish | Mirror Polished, Electropolished, Brushed, No. 4 Satin, Pickled & Passivated | ASTM A240 / Custom |
| Surface Roughness (Ra) | 0.05 μm (mirror) to 0.8 μm (satin) | ASTM A240 |
| Heat Treatment Condition | Annealed (Solution Annealed), Pickled & Passivated | ASTM A269 |
| End Treatment | Plain Cut, Beveled, Threaded, Flanged | Custom / ASTM A269 |
| Corrosion Resistance | Potentiodynamic Polarization (ASTM G5), Cyclic Polarization (ASTM G6) | ASTM G5 / ASTM G6 |
| Hydrostatic Test Pressure | 1.5 × (2 × S × t) / D per ASTM A269 | ASTM A269 |
| Coil Winding Tension | Controlled to prevent ovality & distortion | Manufacturer Specification |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: High-purity stainless steel strip or wire rod is sourced from certified mills with full chemical composition traceability (Mill Test Certificate — MTC).
- Strip Annealing & Cleaning: The incoming strip undergoes solution annealing (typically at 1050–1150°C) followed by acid pickling and passivation to remove mill scale and restore the passive chromium oxide layer.
- Forming (ERW / SAW / Seamless):
- ERW (Electric Resistance Welding): The strip is formed into a tube shape and welded using high-frequency electric resistance, achieving a metallurgically sound weld seam.
- SAW (Submerged Arc Welding): Used for larger diameters and thicker walls, providing deep weld penetration.
- Seamless (Piercing & Pilgering): For applications requiring full integrity without a weld seam.
- Weld Seam Treatment: Internal and external weld beads are ground and polished to achieve a smooth surface profile (Ra ≤ 0.8 μm), minimizing turbulence and stress concentration.
- Sizing & Straightening: Multi-roll sizing units ensure precise dimensional accuracy of OD and wall thickness throughout the coil length.
- Post-Weld Heat Treatment (PWHT): Solution annealing at 1050–1150°C followed by rapid quenching (water or controlled cooling) to achieve a uniform austenitic microstructure with optimal mechanical properties.
- Pickling & Passivation: Immersion in nitric/hydrofluoric acid blend to remove heat treatment scale, followed by passivation to establish a stable Cr₂O₃ passive film.
- Surface Finishing: Depending on the application, the tube may undergo mirror polishing, electropolishing, or brushing.
- Coil Winding: The continuous tube is wound onto precision-machined coil reels under controlled tension to prevent ovality, kinking, or inter-coil contact damage.
- Final Inspection & Testing: Comprehensive non-destructive testing (NDT) and destructive testing protocols are applied (see Section 5).
- Packaging & Dispatch: Coils are wrapped in protective PE film, secured with steel strapping, and palletized for shipment.
4.2 Room Temperature Tensile Testing (Per Standard Methodology)
The Room Temperature Tensile Test Method for Metal Coil Tubes specifies a rigorous protocol for evaluating the tensile properties of coil tubing. Key procedural elements include:
- Specimen Preparation: Test specimens are extracted from the coil at specified intervals (typically every 500 meters or per coil), with the specimen axis aligned parallel to the tube longitudinal axis. Specimen geometry conforms to ASTM E8/E8M or ISO 6892-1.
- Test Environment: Testing is conducted at room temperature (23°C ± 5°C) in a controlled laboratory environment.
- Loading Rate: Strain rate controlled at 0.0005/s to 0.005/s during the yield region to ensure accurate determination of Rp0.2.
- Key Measurements: Proportional limit, yield strength (Rp0.2), ultimate tensile strength (Rm), elongation at break (A), and reduction of area (Z) are recorded.
- Acceptance Criteria: Results must meet or exceed the minimum values specified in the applicable product standard (e.g., ASTM A269 Table 4) for the designated grade and condition.
5. Quality Certifications & Testing Protocols
5.1 Non-Destructive Testing (NDT)
- Eddy Current Testing (ECT): 100% inline inspection of the entire coil length for detection of surface and near-surface defects, weld seam integrity, and dimensional variations. Compliant with ASTM E79 / EN 10216-5.
- Hydrostatic Pressure Testing: 100% hydrostatic proof test at 1.5–2.0 times the maximum design pressure to verify weld seam integrity and wall thickness uniformity. Per ASTM A269 / GB/T 241.
- Visual Inspection: Internal and external visual examination of the weld seam and tube surface for cracks, pits, inclusions, and surface defects.
- Magnetic Particle Inspection (MPI): Applied to ferritic and martensitic grades for detection of surface-breaking defects. Per ASTM E1444.
- Ultrasonic Testing (UT): Spot-check or full-length UT for wall thickness verification and internal defect detection. Per ASTM E1270.
5.2 Destructive Testing
- Tensile Testing: Performed at room temperature per the standard methodology for metal coil tubes (Section 4.2 above). Minimum two specimens per heat/coil.
- Hardness Testing: Vickers or Rockwell B hardness measurement to verify heat treatment condition. Per ASTM E18 / ASTM E92.
- Impact Testing: Charpy V-notch impact testing at specified temperatures (e.g., −29°C / −20°C) for cryogenic applications. Per ASTM E23.
- Flattening Test: Verification of weld seam integrity under radial compression. Per ASTM A269.
- Flaring Test: Assessment of formability and weld seam quality under cold flaring. Per ASTM A269.
5.3 Chemical & Microstructural Analysis
- Chemical Analysis: Spectrometric (OES) and wet chemical analysis of each heat to verify compliance with the specified grade composition. Per ASTM E415.
- Metallographic Examination: Verification of grain size, microstructure homogeneity, and absence of segregation or non-metallic inclusions. Per ASTM E3 / ASTM E406.
- Pitting Corrosion Testing: Ferric chloride (FeCl₃) pitting resistance test to verify the PREN (Pitting Resistance Equivalent Number) of the alloy. Per ASTM G48.