Ultrasonic inspection
Introduction
Ultrasound testing is the examination method that uses the mechanical waves in the elastic state of the material to detect its internal defects.In this test, the elastic wave is transmitted through the metal material and the reflected waves are received by the detector. If there is a defect in the metal, the received wave is distorted, which can be amplified into electric signals by receivers or monitored in real time by automatic image processing equipment. Therefore, the metals internal defects can be found.
Principle
The basic principle of ultrasonic detection is to transmit ultrasonic waves on the surface of the test object, and use the reflection principle to detect the existence and size of defects in the internal structure of the test object. The reason for using ultrasonic waves is that the ultrasonic waves have stronger penetrating power. Additionally, compared with other mediums, the attenuation of ultrasonic waves in metal is still small. When the defect of an object is reflected, the reflected ultrasonic waves will be weakened, and the receiver can detect the reflected ultrasonic waves and express the image of the defect.
Working processes
Ultrasonic inspection can be divided into contact type and non-contact type. For contact type inspection, the workpiece needs to be processed into a particular shape and fit the testing probe. This type of inspection has the advantage of being able to accurately determine the size and shapes of the defect. Usually, a couplant (such as water or oil) needs to be used between the contact surface of the probe and the workpiece to ensure a good transmission of the ultrasonic waves. The most important part of this process lies in the ‘couplant’, which will impact the detection sensitivity.
For non-contact inspection, magnetostriction transducers are used for inspection. Due to the magnetostriction phenomenon, when a magnetostriction transducer is excited by an alternating magnetic field, it will become a generator and emit a high-frequency ultrasonic wave of the same frequency as the excitation source. The magnetostrictive transducer has a relatively large sound pressure, so it can be used for non-contact testing of workpieces with somewhat irregular surfaces. The advantage of this type of inspection is that the testing equipment can be highly automated and that no contact probe is needed to be attached to the test object.
Methods
Ultrasonic detection technology is widely used in ways such as flaw detection and measurement, inspection and control.
Firstly, the method of flaw detection. The advantages of ultrasonic technology are clear: (1)The surface of the test object needs not to be machined,and any shape and size of the test object is workable. (2)Complex components can also be inspected in a very short time without dismantling them. (3)Foreign bodies in the wall or cracks in the internal structure of an object can be accurately detected.
Secondly,the method of thickness measurement and review. If a test object’s appearance is too complex, thickness can be measured by with ultrasonic method. This method also can be used to track the changes in wall thickness of equipments over time.
Thirdly, the application in controlling processes. Ultrasonic detection is often used in the controlling processes, especially in continuous processes. It helps to reduce the quality problems and improve the work efficiency.
Conclusion
Ultrasonic inspection is a very useful technology for the detection of defects, thickness measurement and process control. It is widely used in many industries such as machinery manufacturing, shipping, energy, automotive, aerospace and so on. The main benefit of using this technology is that it can accurately detect the internal defects of an object without any disassembling of the object. Also, this method has very low cost and it can be very automated. Hence, it can be a useful tool for various production processes.
