Stainless Steel Coil Tube — Shield Tunneling Machine (TBM) Main Drive & Cutterhead Piping System
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: No. 604 | Category: Stainless Steel Coil Tube (盘管)
1. Product Overview
The Stainless Steel Coil Tube (Product No. 604) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, continuous-length tubular product specifically designed for the hydraulic, lubrication, and cooling piping systems of Shield Tunneling Machines (TBM), particularly the main drive mechanism and cutterhead assemblies. Unlike conventional straight-length stainless steel pipes, coil tubes are supplied in a coiled configuration, which eliminates the need for field welding or mechanical joining at intermediate points, thereby significantly reducing the risk of leakage and structural failure in high-pressure, high-vibration environments typical of underground tunneling operations.
This product represents a specialized application of stainless steel coil tubing technology within the heavy machinery and tunnel engineering sectors. The coiled form factor allows for flexible routing around complex mechanical assemblies, including the main gear ring, thrust bearing housings, and cutterhead hydraulic circuitry, where space constraints and dynamic load paths demand both geometric adaptability and mechanical robustness.
1.1 Design Philosophy
The design of this coil tube product is guided by the following engineering principles:
- Leak-Free Integrity: The continuous, seamless coiled configuration eliminates butt welds and flanged joints, which are common failure points in high-pressure hydraulic systems operating at pressures exceeding 30 MPa.
- Dynamic Fatigue Resistance: The TBM main drive and cutterhead piping system is subjected to cyclic loading from rotational forces, axial thrust, and ground-induced vibration. The coil tube geometry inherently accommodates cyclic deformation without stress concentration at discrete joints.
- Corrosion Durability: Underground tunneling environments expose piping to moisture, acidic groundwater, and corrosive soil chemistry. Stainless steel alloy composition provides long-term resistance to pitting, crevice corrosion, and general uniform attack.
- Installability: Pre-coiled delivery reduces on-site fabrication time, minimizing construction schedules and reducing the potential for human error during field assembly.
2. Material & Properties
2.1 Alloy Composition
The coil tube is manufactured from Stainless Steel Grade 304 (UNS S30400 / 1.4301) and Stainless Steel Grade 316L (UNS S31603 / 1.4401), selected based on the specific service requirements of the TBM piping application. Grade 316L is preferred for applications involving higher chloride exposure or elevated operating temperatures, owing to the addition of molybdenum which enhances pitting resistance.
| Element | Grade 304 (UNS S30400) | Grade 316L (UNS S31603) |
|---|---|---|
| Carbon (C) — Max | 0.08% | 0.03% |
| Manganese (Mn) — Max | 2.00% | 2.00% |
| Phosphorus (P) — Max | 0.045% | 0.045% |
| Sulfur (S) — Max | 0.030% | 0.030% |
| Chromium (Cr) | 18.00 – 20.00% | 16.00 – 18.00% |
| Nickel (Ni) | 8.00 – 10.50% | 10.00 – 14.00% |
| Molybdenum (Mo) | — | 2.00 – 3.00% |
| Iron (Fe) — Balance | Balance | Balance |
2.2 Mechanical Properties
| Property | Grade 304 (Annealed) | Grade 316L (Annealed) | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 485 MPa | ASTM A270 / EN 10217 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ASTM A270 / EN 10217 |
| Elongation (A50) | ≥ 40% | ≥ 40% | ASTM A270 / EN 10217 |
| Hardness (HV) | ≤ 217 HV | ≤ 217 HV | ASTM A262 |
| Impact Energy (Charpy V-Notch, -40°C) | ≥ 70 J | ≥ 70 J | ASTM A262 |
2.3 Physical & Corrosion Resistance Properties
- Density: 7.93 g/cm³ (Grade 304); 8.03 g/cm³ (Grade 316L)
- Thermal Conductivity: 16.3 W/(m·K) at 100°C (Grade 304); 16.3 W/(m·K) at 100°C (Grade 316L)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (Grade 304); 16.6 × 10⁻⁶ /K (Grade 316L)
- Pitting Resistance (PREN): 19.0 (Grade 304); 24.0 – 26.0 (Grade 316L)
- Maximum Operating Temperature: 870°C (Grade 304); 870°C (Grade 316L)
- Corrosion Resistance: Excellent resistance to atmospheric, fresh water, and mild industrial environments. Grade 316L additionally provides superior resistance to chlorides, acids, and marine environments.
3. Technical Specifications
| Parameter | Specification | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 108 mm (¼" – 4") | ±0.1 mm | ASTM A270 / EN 10217 |
| Wall Thickness | 0.5 mm – 4.5 mm | ±10% | ASTM A270 / EN 10217 |
| Bend Radius (Minimum) | 3D – 5D (D = OD) | — | ASME B31.3 |
| Coil Length | Up to 300 m per coil (continuous) | — | — |
| Surface Finish | Mirror Polish (Ra ≤ 0.4 μm) / Industrial Polish (Ra ≤ 0.8 μm) | — | ASTM A270 |
| Maximum Working Pressure | Up to 63 MPa (9,000 psi) | — | ASME B31.3 / PED 2014/68/EU |
| Temperature Range | -196°C to +870°C | — | ASTM A270 |
| Coil Diameter (Shipping) | 500 mm – 1,200 mm (OD of coil bundle) | ±20 mm | — |
| End Treatment | Plain end / Beveled end / Threaded / Flanged (per customer specification) | — | ASME B31.3 |
| Heat Treatment Condition | Solution Annealed (1010°C – 1150°C, water quenched) | — | ASTM A270 |
| Delivery Condition | Coiled, descaled, passivated, protected wrapping | — | — |
4. Manufacturing Process
4.1 Raw Material Procurement
Raw material takes the form of hot-rolled stainless steel strip conforming to ASTM A240 / EN 10202 specifications. Each heat of steel is accompanied by a Mill Test Certificate (MTC) per EN 10204 Type 3.1, verifying chemical composition and mechanical properties. Incoming material undergoes spectroscopic analysis (OES) for elemental verification and visual inspection for surface defects.
4.2 Cold Forming (Coil Tube Production)
The coil tube is produced through a cold roll-forming process (also known as cold bending or coil tubing forming). The stainless steel strip is fed through a series of precision-ground forming rolls arranged in a sequential bending station. The key steps are:
- Edge Trimming & Deburring: The strip edges are trimmed to exact width tolerance (±0.05 mm) and deburred to prevent burr-induced defects during forming.
- Coil Winding (Forming): The strip is progressively wound around a mandrel through successive roll stations, with each station reducing the bend radius incrementally. This multi-stage forming prevents material thinning, ovality, and springback beyond acceptable tolerances. The forming pressure is carefully calibrated based on the alloy's yield strength and work-hardening behavior.
- Seam Welding: The formed coil tube features a longitudinal seam, which is welded using one of the following methods:
- High-Frequency Induction Welding (HFW): Suitable for larger diameters and thicker walls. The seam is heated to the austenitization temperature by high-frequency current, then plastically upset to achieve metallurgical bond. Typical welding parameters: frequency 400–500 kHz, welding speed 10–30 m/min.
- Argon Arc Seam Welding: Used for smaller diameters or applications requiring superior seam integrity. A continuous argon-protected TIG weld fuses the strip edges with optional filler wire.
- Post-Weld Heat Treatment: The welded coil tube undergoes solution annealing at 1,010°C – 1,150°C followed by rapid water quenching. This process dissolves any precipitated chromium carbides at the weld zone, restores full austenitic microstructure, and eliminates residual stresses introduced during cold forming and welding. The annealing cycle is followed by passivation treatment (nitric acid or citric acid immersion) to form a stable chromium oxide passive film on the surface.
- Dimensional Calibration: The coil tube passes through a final sizing station to correct any ovality or diameter variation introduced during welding and heat treatment. Target ovality is ≤ 1.0% of OD.
4.3 Quality Control & Testing
- Hydrostatic Testing: Each coil tube is subjected to hydrostatic pressure testing at 1.5× the maximum working pressure for a minimum dwell time of 30 seconds. This verifies seam integrity and absence of pinhole defects.
- Eddy Current Inspection (ECI): Automated eddy current probes scan the entire length of the coil tube to detect surface and near-surface defects, including cracks, pits, and seam weld anomalies. Sensitivity is calibrated to detect defects ≥ 0.1 mm in depth.
- Dye Penetrant Testing (PT): Random samples undergo dye penetrant inspection per ASTM E165 to verify the absence of surface-breaking defects at the seam weld zone.
- Dimensional Inspection: Outer diameter, wall thickness, and coil length are verified using laser micrometers and ultrasonic thickness gauges at intervals of 10 m along the coil.
- Surface Roughness Measurement: Optical profilometry verifies surface finish per ASTM A270 requirements.
4.4 Final Processing & Packaging
The finished coil tube is wound onto steel coil carriers, wrapped with moisture-absorbent desiccant paper, and overwrapped with heavy-duty polyethylene film. Each coil is labeled with a unique identification tag containing the product code, material grade, heat number, dimensions, coil length