Stainless steel structural parts are widely used in many industrial fields, and their welding quality directly affects the performance and safety of the entire structure. Post-weld inspection of internal defects is a crucial step in ensuring the quality of stainless steel structural parts. The following details several commonly used inspection methods.
Radiographic inspection is one of the important methods for detecting internal defects in stainless steel structural parts. It mainly utilizes the ability of radiation to penetrate stainless steel structural parts; materials of different densities absorb radiation to varying degrees. When radiation passes through the structural part, it forms an image on a film. If there are defects inside the structural part, such as pores or inclusions, these defective areas absorb relatively less radiation, resulting in different image characteristics on the film compared to normal areas. By carefully observing the image on the film, professional inspectors can accurately determine the location, size, and shape of the defects. Radiographic inspection has the advantage of being highly intuitive, clearly showing the condition of internal defects. However, it also has certain limitations. For example, for some thicker stainless steel structural parts, the penetration ability of radiation is limited, which may affect the inspection results. Furthermore, radiation poses a certain radiation hazard to the human body, requiring strict protective measures during operation.
Ultrasonic testing is also a commonly used method. Its principle utilizes the property that ultrasonic waves, when propagating through stainless steel structural parts, will be reflected, refracted, and scattered when encountering defects. During testing, ultrasonic waves are emitted into the interior of the structural component. When the ultrasonic waves encounter internal defects, some energy is reflected back. By receiving and analyzing these reflected waves, the location and approximate condition of the defect can be determined. Ultrasonic testing has high sensitivity for detecting planar defects such as internal cracks, and the equipment is relatively portable and flexible in operation, capable of inspecting stainless steel structural components of different shapes and sizes. However, ultrasonic testing requires highly skilled personnel who need professional training to accurately interpret the test results. Furthermore, for some complex-shaped structural components, the propagation path of the ultrasonic waves may be affected, increasing the difficulty of testing.
Magnetic particle testing is mainly suitable for detecting surface and near-surface defects in stainless steel structural parts. Although stainless steel itself has weak magnetism, some stainless steel structural parts can be tested using magnetic particle testing after special treatment. When a structural component is magnetized, if surface or near-surface defects exist, the magnetic field lines will be distorted at the defect locations, generating a leakage magnetic field. At this point, magnetic powder is sprinkled on the surface of the structural component. The powder is attracted by the leakage magnetic field, forming a clear magnetic trace, thus revealing the location and shape of the defect. Magnetic particle inspection is simple to operate and low in cost, and can quickly detect tiny surface and near-surface defects. However, it can only detect ferromagnetic materials and is not suitable for non-ferromagnetic stainless steel structural parts. Furthermore, its detection depth is limited, primarily targeting surface and near-surface defects.
Penetrating inspection utilizes the capillary effect of liquids to detect surface opening defects in stainless steel structural parts. A penetrant containing fluorescent or colored dye is applied to the surface of the structural component. After a certain period of time, the penetrant seeps into the surface opening defect. Excess penetrant is then removed from the surface, and a developer is applied. The developer absorbs the penetrant from the defect, and under a specific light source, a clear trace appears at the defect location. Penetrant inspection is not limited by the material or shape of the structural component and can detect surface opening defects in various non-porous materials. It is relatively simple to operate, but it can only detect surface opening defects and cannot detect internally closed defects.
In actual testing, it is often necessary to comprehensively select appropriate testing methods based on the specific circumstances of the stainless steel structural parts, such as material, thickness, shape, and expected defect types. Sometimes, multiple testing methods are combined to improve the accuracy and reliability of defect detection and ensure that the quality of the stainless steel structural parts meets the requirements.
