Traditional MFL inspection typically employs DC or low‑frequency magnetization, and is primarily suitable for detecting macroscopic defects in thick‑walled workpieces. However, with the continuous upgrading of industrial quality requirements—such as increased pipe wall thickness, higher inspection speeds, and more stringent demands for detecting micro‑cracks and near‑surface defects—the limitations of conventional low‑frequency MFL are becoming increasingly evident.
The core breakthrough of high‑frequency MFL technology lies in raising the excitation frequency (from the conventional 6–7 kHz up to 10 kHz–100 kHz), which concentrates the magnetic field energy more intensely in the near‑surface region of the workpiece. This significantly enhances the detection sensitivity for tiny surface and sub‑surface defects. This technological pathway is emerging as a key breakthrough opportunity for domestically manufactured MFL inspection equipment to achieve a "curve‑overtaking" (leapfrog advancement) in the global market.
II. Technological Breakthrough: A Leap from "Following" to "Leading"1. Order‑of‑magnitude increase in operating frequency
Currently, the domestically developed high‑frequency AC MFL technology can operate at frequencies ranging from 10 kHz to 100 kHz, far exceeding the 6–7 kHz typical of mainstream international products. This implies:
Higher operating frequency → shallower skin depth → magnetic field energy more concentrated in the near‑surface region → stronger signal response to minute surface cracks.
Under the 100 kHz excitation field generated by an arrayed‑wire magnetizer, the near‑surface zone of the workpiece is placed in a magneto‑quasistatic field. Above the crack, there exists not only an AC leakage magnetic field but also a perturbing field induced by eddy currents, resulting in richer defect signal characteristics.
2. Magnitude improvement in detection precision
The capability of high‑frequency MFL to detect tiny cracks has achieved a qualitative leap:
Simulation studies indicate that micro‑cracks as small as 0.1 mm in width and 1 mm in depth can produce identifiable leakage magnetic field signals.
High‑speed MFL inspection tests for cracks have demonstrated that within a speed range of up to 200 km/h, rapid inspection can detect cracks with a width as small as 0.2 mm and a depth as small as 2 mm.
The following is a comparison data between a high-frequency magnetic leakage detection system based on actual technical parameters and similar equipment such as Tuboscope and Foerster
| serial number | Compare points | United States TUBOSCOPE |
Germany FÖERSTER |
this project | |
| 1. | Maximum detected wall thickness |
15mm |
15mm |
25mm |
|
| 2. | Detection Sensitivity for Internal & External Cracks (Percentage of Wall Thickness) | External Crack Depth |
5% |
5% |
5% |
| Internal Cracks for 10mm Wall Thickness |
5% |
5% |
5% |
||
| Internal Cracks for 12.5mm Wall Thickness | 10% | 10% | |||
| Internal Cracks for 15mm Wall Thickness | 15% | 12.5% | 10% | ||
| Internal Cracks for 25mm Wall Thickness | Cannot detect | Cannot detect | 15% | ||
| 3. | Maximum testing speed |
1.5m/s |
1.5m/s |
3.0m/s | |
Doubled inspection wall thickness: The domestically produced high-frequency MFL system can inspect wall thicknesses up to 25 mm, nearly 1.7 times that of Tuboscope and Foerster (both limited to 15 mm). This means that thick-walled steel pipes previously undetectable by MFL methods can now be inspected online in a non‑destructive manner.
A "zero‑to‑one" breakthrough in detecting internal cracks in thick walls: For internal cracks in 25 mm thick steel pipes, neither Tuboscope nor Foerster can provide reliable detection, whereas the domestic high‑frequency MFL system achieves a sensitivity of 15% of wall‑thickness depth for internal crack detection.
Doubled inspection speed: The maximum inspection speed reaches 3.0 m/s – twice that of imported equipment (1.5 m/s). For domestic oil‑well pipe manufacturers whose production lines run at speeds up to 8 m/s, this means that the inspection step no longer constitutes a production bottleneck.
Breakthroughs in high‑frequency MFL technology deliver tangible value to our customers in the following ways:
| Application scenarios | Pain points of traditional solutions | High frequency magnetic leakage solution |
| Thick walled steel pipe detection (>15mm) | Imported equipment cannot be detected or has insufficient accuracy | 25mm wall thickness full coverage detection |
| High speed production line online inspection | The detection speed cannot keep up with the pace of the production line | 3.0m/s flaw detection speed, matching high-speed production |
| Detection of surface micro cracks | Low frequency magnetic leakage is insensitive to shallow defects | High frequency magnetization focuses on the surface layer, and micrometer level defects can be identified |
| Rough surface inspection | The lift off effect leads to severe signal attenuation | High frequency signals are more robust to lift off changes |
Our high‑frequency MFL inspection solutions serve both civilian sectors—including petrochemical, coal, special equipment, and steel pipe manufacturing—and military applications, such as ferromagnetic components in the defense industry. Notably, Chinese manufacturers represent 46.4% of the global oil well pipe market, with production lines operating at speeds up to 8 m/s—making rapid, reliable inspection an immediate priority. The domestic breakthrough in high‑frequency MFL technology offers these companies a strategic advantage, enabling them to safeguard product quality while unlocking full production capacity.
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