Overview
Ultrasonic testing is a very common nondestructive testing method for metal materials. However, do you have a clear understanding of the purpose and principles of ultrasonic testing? This article will provide a detailed introduction to this simple and efficient testing method, and explain its principles.
What are Defects?
Generally speaking, qualified metal materials should be completely solid and have a uniform structure. However, during the actual production process, metal materials often develop defects.
For example, during casting, bubbles may be present in the molten metal. After solidification, these bubbles form pores. During certain deformation processes or welding, deep cracks may form in the metal due to extrusion or melting.
Some surface defects, such as scratches and abrasions, do not affect the material's performance. However, the impact of pores and cracks cannot be ignored. On the one hand, these defects can become the starting point for corrosion, which can spread outward along the defects, affecting the entire metal. On the other hand, defects like cracks are highly susceptible to stress and can cause metal fracture under long-term operation.
Therefore, it is crucial to detect defects after the material is produced. Ultrasonic testing is the most commonly used defect detection method.
The Principle of Ultrasonic Flaw Detection.
Ultrasonic waves are special sound waves that are inaudible to the human ear. They can penetrate metal. Ultrasonic testing involves allowing ultrasound waves to penetrate metal and determining whether there are defects based on the ultrasound waveform. A key characteristic of ultrasonic waves is that their waveform changes when they pass through the interface between two different media.
Thus, if the ultrasound waveform changes within metal, it indicates the presence of cracks. These cracks are the metal defects we need to detect.
Conversely, if the waveform remains unchanged, the metal material is qualified.
The diagram below illustrates the principle of ultrasonic testing. Ultrasonic waves undergo two waveform changes when entering and exiting metal. Any change in the waveform between these two changes indicates a defect has been detected.
Which Materials Require Ultrasonic Testing?
Round Bars
Round bars are typically solid metals, making them well-suited for ultrasonic testing. Generally, round bars require ultrasonic testing after smelting and forging.
Plate
Plate is a relatively thin and bulky material, making ultrasonic testing of finished plates difficult. Generally, ultrasonic testing is performed on the billet before rolling. If the billet is defect-free, the rolled plate will also be defect-free.
Wire
Wire is a relatively thin material, making it difficult to inspect ultrasonically. However, like plate, it requires ultrasonic testing of the billet as it is manufactured.
FAQ
What is nondestructive testing?
Nondestructive testing refers to testing methods that do not damage the material. Its counterpart is destructive testing, such as tensile testing, which involves stretching the material until it breaks. Hardness testing, for example, involves creating an indentation in the material.
Does passing ultrasonic testing mean a material is qualified?
Ultrasonic testing only detects defects in the material and does not guarantee that the material's performance meets standards. For this purpose, other testing methods, such as chemical analysis and tensile testing, are also required.
Further Reading
Conclusion
Ultrasonic testing is a common metal detection method. It is used to detect defects such as pores and cracks within metals. The principle of ultrasonic testing is to observe the presence of defects using changes in the ultrasonic wave waveform. Generally, ultrasonic testing is performed on bars. Plate billets and wire billets also require ultrasonic testing.
We produce materials strictly in accordance with standards and can perform professional ultrasonic testing. Please contact us with any inquiries.
