Zhuojin Pipe Fitting Co., LtdApplication of Array Magnetic Flux Leakage Detection in Seamless Steel Pipe Quality Inspection
Literature Overview
This paper published in Physical Testing (Vol. 43, Issue 4, 2025, pp. 10–16) by Fan Qinghui, Zhou Changzhong, and Wang Wei from Baoshan Iron and Steel Co., Ltd. presents an innovative array magnetic flux leakage (AMFL) detection system designed to overcome the limitations of conventional magnetic flux leakage (MFL) methods in identifying short and oblique defects in seamless steel pipes. The system employs multi-dimensional signal acquisition and fusion processing to significantly enhance detection precision and efficiency.
System Architecture and Technical Configuration
The AMFL system described in the paper comprises several key subsystems:
| Subsystem | Function | Key Features |
|---|---|---|
| Transverse MFL system | Detects longitudinal surface and near-surface defects | Array sensor configuration for high spatial resolution |
| Longitudinal MFL system | Detects transverse surface and near-surface defects | Multi-pole magnetization arrangement |
| Three-roller centering conveyor | Pipe transportation and alignment | Ensures consistent pipe-to-sensor gap |
| Main unit mounting platform | System integration and vibration isolation | Precision mechanical design |
The horizontal and vertical MFL systems work in concert to provide comprehensive coverage of both internal and external pipe surfaces. The array sensor configuration represents a fundamental advancement over traditional single-probe MFL methods, as it captures magnetic field gradients in multiple directions simultaneously.
Detection Performance and Validation Results
The system was validated using comparison sample pipes containing artificial defects of various orientations and dimensions. The test results demonstrate remarkable detection capabilities:
- Longitudinal defects: 100% detection rate for defects with length ≥ 12 mm
- Transverse defects: 100% detection rate for defects with length ≥ 12 mm
- Oblique defects: 100% detection rate for defects with length ≥ 25 mm
The paper emphasizes that conventional MFL methods struggle with oblique defects because the magnetic flux perturbation is distributed across multiple sensor channels, reducing the signal amplitude below reliable detection thresholds. The array approach resolves this limitation by capturing the full spatial distribution of the flux perturbation and applying signal fusion algorithms to reconstruct defect geometry.
Signal Processing and Defect Identification
The multi-dimensional signal acquisition provides rich information content that enables sophisticated signal processing:
- Signal-to-noise ratio (SNR) optimization: The array configuration inherently improves SNR through spatial averaging and coherent signal detection.
- Repeatability assessment: The system demonstrates consistent detection performance across multiple passes, which is critical for production line applications where pipes may need re-inspection.
- Defect discrimination: The multi-channel data allows differentiation between true defects and geometric features (such as weld seams, dimensional variations, and handling marks).
Engineering Practice Integration
For seamless pipe manufacturers and end-users, this AMFL technology offers several practical advantages:
- Full lifecycle quality monitoring: The system can be deployed at multiple stages—from mill exit to in-service inspection—providing continuous quality tracking.
- Reduced false rejection rates: Improved defect discrimination reduces unnecessary pipe rejection, improving yield and reducing costs.
- Oblique defect detection: This addresses a critical gap in conventional MFL inspection, particularly for pipes subjected to torsional or bending stresses that may initiate oblique surface cracks.
- Integration with automated sorting: The high detection accuracy and repeatability make the system suitable for integration with automated pipe sorting and rejection systems.
Key Reflections
The transition from single-probe to array-based MFL detection represents a paradigm shift in non-destructive testing for seamless steel pipes. The ability to achieve 100% detection rates for defects as short as 12 mm in the axial direction and 25 mm for oblique defects is a significant advancement. From an engineering perspective, the practical implementation of this system requires careful consideration of pipe diameter range, surface condition (rust, scale, coating), and production line speed constraints. The three-roller centering conveyor is particularly important for maintaining consistent coupling between the magnetic field and pipe surface, as variations in pipe-to-sensor distance directly affect detection sensitivity. This technology holds substantial promise for enhancing the safety and reliability of seamless pipes used in high-pressure applications such as oil and gas pipelines, pressure vessels, and structural applications.