TP2 Stainless Steel Coil Tube — Flaw Detection & Identification Technology Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: No. 448
Classification: Technical Literature & Process Research
Reference Document: "Key Technology Research on Flaw Detection and Marking of TP2 Coil Tubes"
1. Product Overview
The TP2 Stainless Steel Coil Tube is a precision-manufactured austenitic stainless steel tubing product supplied in coil form, designed for high-volume, continuous processing applications. This product represents a critical segment within the stainless steel pipe and tube industry, combining the excellent corrosion resistance and formability of TP2-grade austenitic stainless steel with the logistical and manufacturing advantages of coil configuration.
Coil tubes (Coiltube) are delivered in continuous wound lengths, eliminating the need for individual cut-length handling and enabling seamless integration into downstream forming, welding, and machining operations. The coil form factor significantly reduces material waste, minimizes handling damage, and optimizes production throughput for high-volume manufacturing environments.
A central focus of this product line is the implementation of advanced non-destructive testing (NDT) methodologies and traceability marking systems. The research and development efforts documented under the title "Key Technology Research on Flaw Detection and Marking of TP2 Coil Tubes" address the critical challenge of ensuring full-length integrity verification across continuous coil products — a problem that presents unique difficulties compared to discrete cut-length tubing.
2. Material & Properties
2.1 Material Designation
TP2 is the Chinese national standard (GB/T 20878) designation for austenitic stainless steel, corresponding to the international equivalents:
- UNS S30408 (American Iron and Steel Institute — AISI 304)
- 1.4301 (European Numbering System — EN 10088-1)
- X5CrNi18-10 (European designation)
TP2 is a low-carbon variant of the 304 stainless steel family, with a carbon content limited to ≤0.08% to prevent intergranular corrosion during welding and high-temperature exposure.
2.2 Chemical Composition (GB/T 20878)
| Element | Specification (%) | Typical Value (%) |
|---|---|---|
| Carbon (C) | ≤ 0.08 | 0.04 – 0.06 |
| Manganese (Mn) | ≤ 2.00 | 0.50 – 1.00 |
| Silicon (Si) | ≤ 1.00 | 0.15 – 0.30 |
| Chromium (Cr) | 18.00 – 20.00 | 18.50 – 19.50 |
| Nickel (Ni) | 8.00 – 10.00 | 8.50 – 9.50 |
| Nitrogen (N) | ≤ 0.10 | 0.02 – 0.05 |
| Sulfur (S) | ≤ 0.03 | 0.010 – 0.020 |
| Phosphorus (P) | ≤ 0.035 | 0.015 – 0.025 |
2.3 Mechanical Properties
| Property | Specification | Unit |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 | MPa |
| Yield Strength (Rp0.2) | ≥ 205 | MPa |
| Elongation (A) | ≥ 40 | % |
| Hardness (HBW) | ≤ 210 | — |
| Density | 7.93 | g/cm³ |
2.4 Physical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 300 K
- Specific Heat Capacity: 500 J/(kg·K) at 300 K
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (10–500 °C)
- Electrical Resistivity: 0.72 Ω·mm²/m
- Magnetic Susceptibility: Non-magnetic (austenitic microstructure)
2.5 Corrosion Resistance
TP2 stainless steel exhibits excellent resistance to atmospheric corrosion, weakly acidic and alkaline environments, and non-oxidizing organic acids. The passive chromium oxide film (Cr₂O₃) formed on the surface provides a self-healing protective layer in oxidizing environments. However, TP2 is not recommended for sustained exposure to chloride-rich environments (e.g., seawater) where pitting and crevice corrosion may occur, as the molybdenum-free composition lacks the enhanced pitting resistance of TP316 (316L) grade.
3. Specifications
3.1 Geometric Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ159.0 mm | GB/T 14976, GB/T 14975 |
| Wall Thickness (WT) | 0.30 mm – 12.00 mm | GB/T 14976 |
| OD Tolerance | ±0.05 mm (precision grade) / ±0.5% (standard grade) | GB/T 14976 |
| Wall Thickness Tolerance | ±0.05 mm (precision grade) / ±10% (standard grade) | GB/T 14976 |
| Coil Length (per roll) | 15 m – 300 m (configurable) | Manufacturer specification |
| Coil Inner Diameter | Φ102 mm / Φ150 mm / Φ200 mm | Manufacturer specification |
| Coil Outer Diameter (max) | Φ1200 mm | Manufacturer specification |
| End Form | Flat cut / Beveled / Welded closure | Customer requirement |
3.2 Surface Finish Options
| Finish Designation | Description | Surface Roughness (Ra) | Application |
|---|---|---|---|
| 2B (Cold Rolled) | Standard cold-rolled finish with matte appearance | ≤ 0.50 μm | General industrial use |
| BA (Bright Annealed) | Smooth, reflective surface with no pickling marks | ≤ 0.25 μm | Decorative, food-grade |
| HL (Hairline) | Uniform unidirectional brushed texture | 0.30 – 0.80 μm | Architectural, decorative |
| No.4 (Brushed) | Medium-grit abrasive finish | 0.40 – 0.80 μm | General decorative |
| 8K (Mirror) | High-polish mirror finish | ≤ 0.05 μm | High-end decorative, optical |
| Pickled (Pickling) | Acid-cleaned matte surface, oxide scale removed | ≤ 0.80 μm | Post-welding applications |
3.3 Applicable Standards
| Standard | Title / Scope |
|---|---|
| GB/T 14976-2012 | Steel seamless tubes for fluid transport |
| GB/T 14975-2002 | Steel seamless tubes for cold-rolled stainless steel |
| GB/T 20878-2007 | Chemical composition and product designation for stainless steels |
| GB/T 4730.2-2005 | Non-destructive testing — Magnetic particle testing |
| GB/T 4730.3-2005 | Non-destructive testing — Ultrasonic testing |
| GB/T 4730.5-2005 | Non-destructive testing — Eddy current testing |
| GB/T 4730.6-2005 | Non-destructive testing — Radiographic testing |
| ASTM A213/A213M | Standard specification for austenitic stainless steel tubes |
| EN 10216-5 | Heat-resistant, hydraulic, and mechanical tubing — Stainless steel |
| ISO 7868 | Stainless steel tubes and pipes — General specifications |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Procurement: Virgin stainless steel billets or continuously cast slabs conforming to TP2 composition requirements are sourced from certified mills with full traceability documentation (Heat Number / 炉号 tracking).
- Hot Rolling / Piercing: Billets are heated to 1150–1250 °C and hot-rolled into seamless tube blanks with controlled wall thickness and outer diameter.
- Pickling & Annealing: The hot-rolled tube undergoes acid pickling (HNO₃ + HF blend) to remove mill scale and oxide layers, followed by solution annealing at 1050–1100 °C in a protective atmosphere to restore full austenitic microstructure and corrosion resistance.
- Cold Drawing / Cold Rolling: The annealed tube is cold-worked through progressively reducing dies or rollers to achieve precise dimensional tolerances (±0.05 mm) and improved mechanical properties. Multiple passes are typical for thin-wall coil tubes.
- Intermediate Annealing: Periodic solution annealing treatments are performed between cold-working passes to relieve accumulated cold-work strain, prevent cracking, and maintain ductility.
- Final Annealing: A final solution anneal at 1050–1100 °C in a controlled atmosphere (nitrogen or vacuum) ensures uniform microstructure and optimal mechanical properties.
- Surface Treatment: Final surface finishing (2B, BA, HL, No.4, or 8K) is applied according to customer specifications.
- Non-Destructive Testing (NDT): Full-length inspection of the coil tube using multiple NDT methods (see Section 4.2).
- Flaw Marking & Traceability: Defect locations are precisely marked and recorded (see Section 4.3).
- Coiling & Packaging: The inspected tube is wound onto coils with controlled tension, wrapped in protective film, and packaged with identification labels.
4.2 Non-Destructive Testing (NDT) — Key Technology
The research documented under