In the field of modern architecture and engineering, steel structural components are widely used due to their advantages such as high strength, lightweight, and good plasticity. However, during the manufacturing, transportation, and installation of steel structural components, surface defects such as cracks, rust, and slag inclusions may occur due to various reasons. These defects not only affect the aesthetics of the components, but more importantly, they can reduce their load-bearing capacity and service life, and even cause safety accidents. Therefore, surface defect detection of steel structural components is crucial. Among various detection methods, magnetic particle inspection has become a commonly used method for detecting surface defects in steel structural components due to its high sensitivity and easy operation.

1、 The basic principle of magnetic particle inspection
Magnetic particle inspection is a non-destructive testing method that uses the principle of magnetic field induction to detect surface and near surface defects in ferromagnetic materials. When ferromagnetic materials are magnetized, their internal magnetic field lines will be distributed along the direction of higher magnetic permeability of the material. If there are defects in the material, such as cracks, pores, or non-metallic inclusions, these defects can cause air gaps or non-magnetic gaps on the material, leading to a significant increase in magnetic resistance and affecting the normal propagation of magnetic field lines. According to the principle of magnetic continuity, magnetic field lines will change their path and escape from the workpiece, forming a leakage magnetic field. The strength of the leakage magnetic field is related to the magnetization field strength and the degree of influence of defects on the perpendicular cross-section of the magnetization field. By applying magnetic powder on the surface of the workpiece, the magnetic powder will be adsorbed by the leakage magnetic field, forming visible magnetic traces under appropriate lighting, thereby displaying the location, shape, and size of defects.
2、 Operation steps of magnetic particle inspection
The operation steps of magnetic particle inspection mainly include pretreatment, magnetization, application of magnetic particles, observation and recording, etc.
Preprocessing: Preprocessing is the primary step in magnetic particle inspection, aimed at removing impurities such as grease, paint, and rust from the surface of components to ensure that magnetic particles can accurately adhere to defects. The pre-treatment methods include sandblasting, polishing, solvent cleaning, etc.
Magnetization: Magnetization is a crucial step in magnetic particle inspection. By applying a magnetic field to achieve saturation magnetization of the workpiece, a sufficiently strong leakage magnetic field can be generated. The methods of magnetization include circumferential magnetization, longitudinal magnetization, composite magnetization, and rotational magnetization. The specific choice of method depends on the shape, size, and defect properties of the workpiece.
Applying magnetic powder: Applying magnetic powder is carried out after magnetization. Magnetic powder can be dry powder or wet powder, depending on the testing environment and operational requirements. After applying magnetic powder, it will adhere to the defect under the action of leakage magnetic field, forming magnetic marks.
Observation record: Observation record is the final step of magnetic particle inspection. Under appropriate lighting conditions, use a magnifying glass or magnetic particle inspection lamp to observe magnetic traces and record the location, shape, and size of defects. For important components or complex defects, photography or video recording can also be used for recording.
3、 Application of Magnetic Particle Testing in Steel Structure Component Inspection
Magnetic particle inspection has a wide range of applications in the testing of steel structural components. It can effectively detect defects such as cracks, inclusions, and folds on the surface and near surface of steel structural components. These defects often have a serious impact on the load-bearing capacity and service life of the components. Through magnetic particle inspection, these defects can be detected and dealt with in a timely manner, improving the quality and safety of the components.
Magnetic particle inspection is also applicable for regular inspection and maintenance of steel structural components. During long-term use, steel structural components may develop new defects due to fatigue, corrosion, and other reasons. Through regular magnetic particle inspection, potential safety hazards can be detected and addressed in a timely manner, ensuring the normal operation of the components.
In addition, magnetic particle inspection can also be used for quality control and acceptance of steel structural components. During the manufacturing and installation process, magnetic particle inspection of components can ensure their compliance with design requirements and quality standards, improving the quality and safety of the project.
4、 Conclusion
Magnetic particle inspection, as a highly sensitive and easy-to-use non-destructive testing method, has broad application prospects in the detection of surface defects in steel structural components. Through magnetic particle inspection, defects on the surface of steel structural components can be detected and treated in a timely manner, improving the quality and safety of the components, reducing maintenance costs, and extending their service life. Therefore, in the field of steel structure engineering, the application and promotion of magnetic particle inspection technology should be strengthened to provide strong guarantees for the safe operation of steel structure engineering.