Stainless Steel Coil Tube for High-Pressure Concrete Pumping Systems (C130 Vertical 880m Application)
1. Product Overview
The Stainless Steel Coil Tube (Product No. 753) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubular product designed for demanding industrial applications, particularly in ultra-high-pressure concrete pumping systems. This product was developed in direct response to the groundbreaking achievement of China's first successful C130 concrete simulated vertical 880m pumping experiment, which demonstrated the capability to pump ultra-high-strength concrete to extraordinary heights in supertall construction projects.
Unlike conventional straight-length stainless steel pipes, coil tubes are supplied in continuous coiled form, offering significant advantages in terms of flexibility, space efficiency during transportation and storage, and reduced waste during field installation. The coiled configuration allows for smooth, continuous deployment in applications requiring long uninterrupted runs without the need for multiple joints or couplings.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected specifically for its exceptional combination of mechanical strength, corrosion resistance, and fatigue performance under cyclic loading conditions inherent to high-pressure pumping operations.
2.1 Base Material Specifications
- Primary Grades: AISI 304 (UNS S30400), AISI 316L (UNS S31603), and AISI 321 (UNS S32100)
- Carbon Equivalent (CE): ≤ 0.04% for enhanced weldability and reduced susceptibility to intergranular corrosion
- Nickel Content: 8.0–10.5% (minimum), providing superior resistance to chloride-induced pitting
- Chromium Content: 18.0–20.0%, ensuring robust passive film formation and general corrosion resistance
- Molybdenum Content (316L grade): 2.0–2.5%, further enhancing resistance to aggressive chemical environments
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (304 grade); ≥ 530 MPa (316L grade)
- Yield Strength (0.2% offset): ≥ 205 MPa (304); ≥ 215 MPa (316L)
- Elongation at Break: ≥ 40% (minimum), ensuring adequate ductility for cold forming and coiling operations
- Hardness: ≤ 220 HV (annealed condition)
- Fatigue Endurance Limit: ≥ 150 MPa (at 10⁷ cycles), critical for withstanding repetitive pressure cycling in pumping applications
- Impact Toughness (Charpy V-Notch at -40°C): ≥ 47 J, demonstrating excellent low-temperature performance
2.3 Physical Properties
- Density: 7.93 g/cm³
- Thermal Conductivity (25°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
- Specific Heat (25°C): 0.50 J/(g·K)
- Electrical Resistivity (20°C): 7.4 × 10⁻⁷ Ω·m
2.4 Corrosion Resistance
- Pitting Resistance Equivalent Number (PREN): ≥ 24 (316L grade), calculated as PREN = %Cr + 3.3×%Mo + 16×%N
- Intergranular Corrosion Resistance: Complies with ASTM A240/A240M Section 6 requirements (6% HCl test)
- Crevice Corrosion Resistance: Superior performance in chloride-containing environments
- Stress Corrosion Cracking (SCC) Resistance: Excellent resistance in chloride environments below 60°C
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ12 mm – Φ168.3 mm | ASTM A554 / A554M |
| Wall Thickness (WT) | 0.5 mm – 6.0 mm | ASTM A554 / A554M |
| OD Tolerance | ±0.05 mm (≤ Φ50 mm); ±0.10 mm (> Φ50 mm) | ASTM A554 Section 7.2 |
| Wall Thickness Tolerance | ±10% of nominal (≤ 1.0 mm); ±0.10 mm (> 1.0 mm) | ASTM A554 Section 7.3 |
| Coil Weight | 500 kg – 5,000 kg per coil | Manufacturer specification |
| Coil Inner Diameter (CID) | Φ300 mm – Φ1,000 mm | Manufacturer specification |
| Surface Finish | 2B (cold-rolled and annealed), No. 4 brushed, or BA (Bright Annealed) | ASTM A480 / A480M |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.4 μm (polished); ≤ 0.2 μm (electropolished) | ISO 1302 |
| Maximum Operating Pressure | Up to 25 MPa (3,626 psi) — validated for 880m vertical pumping | GB/T 24511 / EN 13480 |
| Operating Temperature Range | -196°C to +600°C | ASME BPV Code Section VIII |
| Seam Type | Welded (TIG/ARGON) or Seamless | ASTM A554 / A554M |
| Weld Integrity | 100% radiographic testing (RT) or eddy current testing (ECT) | ASME BPV Code Section VIII Div. 1 UW-51 |
| End Condition | Plain cut, beveled (ASME B16.25), or thread-protected | ASME B16.25 |
| Coiling Direction | Right-hand coil (standard); Left-hand coil (special order) | Manufacturer specification |
| Maximum Length per Coil | Up to 2,000 m (continuous) | Manufacturer specification |
3.1 Dimensional Tolerances (Detailed)
| OD Range (mm) | OD Tolerance (mm) | WT Tolerance (mm) | Out-of-Roundness (mm) | Straightness (mm/m) |
|---|---|---|---|---|
| 6.0 – 12.0 | ±0.03 | ±10% | 0.05 | 0.5 |
| 12.1 – 25.0 | ±0.05 | ±10% | 0.08 | 0.5 |
| 25.1 – 50.0 | ±0.05 | ±10% | 0.10 | 0.5 |
| 50.1 – 100.0 | ±0.10 | ±0.10 | 0.15 | 1.0 |
| 100.1 – 168.3 | ±0.10 | ±0.15 | 0.20 | 1.0 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement & Incoming Inspection: Hot-rolled stainless steel strip or coil is sourced from certified mills (e.g., Outokumpu, POSCO, Tsingshan). Each batch undergoes 100% chemical analysis (Spectroscopy, ASTM E1903/E4152) and mechanical testing to verify compliance with specified grade requirements.
- Pickle & Passivate (P&P): The cold-rolled strip is subjected to acid pickling (typically HNO₃/HF mixture) followed by passivation to remove surface contaminants, scale, and to establish a stable chromium oxide passive film. This step is critical for ensuring corrosion resistance from the outset.
- Cold Forming & Pipe Making: The strip is fed through a series of progressively reducing roll sets (roll-forming) or a tube mill (for seamless production). For welded coil tubes, a longitudinal weld is created using TIG (Tungsten Inert Gas) or GTAW (Gas Tungsten Arc Welding) with high-purity argon shielding gas (≥ 99.995% purity).
- Heat Treatment (Solution Annealing): The formed tube is solution annealed at 1,010–1,150°C followed by controlled cooling (water quench or air cool depending on grade). This eliminates cold-work hardening, relieves internal stresses, and restores full austenitic microstructure and mechanical properties.
- Precision Sizing & Straightening: The annealed tube passes through a cold-sizing (triple-roller) mill to achieve final dimensional tolerances. This process also corrects any minor deviations in roundness or straightness.
- Surface Finishing: Depending on application requirements, the tube may undergo additional surface treatments including mechanical polishing, electropolishing, or passivation treatment to achieve specified surface roughness and corrosion resistance levels.
- Coiling: The finished tube is wound onto a coil former at controlled tension to produce the final coil configuration. Coil dimensions (inner diameter, weight) are optimized based on downstream application requirements and transportation logistics.
- Final Inspection & Testing: Comprehensive quality verification including dimensional measurement, surface inspection, pressure testing, and non-destructive testing (NDT) prior to packaging and shipment.
4.2 Key Process Parameters
- Welding Shielding Gas: Argon ≥ 99.995% purity, flow rate 12–20 L/min
- Weld Heat Input: Controlled at 0.8–1.5 kJ/mm to minimize thermal distortion and maintain weld integrity
- Annealing Atmosphere: Controlled hydrogen (H₂) or vacuum atmosphere to prevent scale formation
- Coiling Tension: 3–8 kN/m, optimized to prevent coil springback and maintain dimensional stability
- Hydrostatic Pressure Test: 1.5× maximum design pressure for 30 seconds, with zero leakage tolerance
4.3 Non-Destructive Testing (NDT) Protocol
- 100% Eddy Current Testing (ECT): Per ASTM E3097, for detection of surface and near-surface defects in welded tubes
- 100% Hydrostatic Pressure Testing: Per ASTM A554 Section 12, at 1.5× working pressure
- 10% Radiographic Testing (RT): Per ASTM E94, for weld seam integrity verification (or 100% for critical applications)
- Magnetic Particle Inspection (MT): Per ASTM E709, for ferromagnetic detection of surface discontinuities (where applicable)
- Ultrasonic Testing (UT): Per ASTM E213, for wall thickness measurement and internal defect detection
5. Applications
5.1 Ultra-High-Pressure Concrete Pumping (Primary Application)
The defining application of this coil tube is in the C130 ultra-high-strength concrete pumping system for vertical pumping to heights exceeding 880 meters. In this application, the coil tube serves as the delivery pipeline within the pumping apparatus, transporting concrete slurry under extreme hydraulic pressures. Key performance requirements include:
- Withstand cyclic pressure loading of up to 25 MPa without fatigue failure
- Resist abrasive wear from aggregate particles within the concrete slurry
- Maintain dimensional stability under sustained internal pressure
- Provide smooth internal surface to minimize pumping resistance and concrete segregation
- Resist corrosion from cementitious alkaline environment (pH 12–13)
5.2 Additional Industrial Applications
- Oil & Gas Industry: Subsea pipelines, wellhead flowlines, and process piping in offshore platforms
- Chemical Processing: Reactor feed lines, heat exchanger tubing, and corrosive fluid transfer systems
- Food & Pharmaceutical: Hygienic process piping, CIP (Clean-In-Place) compatible systems
- Building Construction: Structural tubing, architectural cladding, and decorative applications in supertall buildings
- Automotive: Exhaust systems, fuel lines, and hydraulic brake lines
- Power Generation: Steam lines, condensate piping, and nuclear-grade components
- Marine & Offshore: Ballast systems, seawater intake piping, and desalination plant tubing
5.3 880m Vertical Pumping — Technical Context
The C130 concrete simulated vertical 880m pumping experiment represents a landmark