Ultrasonic flaw detection
Ultrasound proved its highest efficiency in the following types of control of parts and structures:
- Quality control of welded joints of metal structures
- Ultrasonic thickness gauging in a wide variety of industries and laboratory research
- Ultrasonic flaw detection of rails and welds for railways, as well as rails for trams
- Ultrasonic inspection of wheel sets for railway cars and trams.
- Input inspection of pipes of different diameters
- Spot welding of metal structures
- Ultrasonic inspection of castings in the metallurgical sector
Ultrasonic inspection of welded joints and materials is based on the possibility of ultrasound propagation in the controlled article, reflected from the boundaries of materials and internal defects. Sound waves in a homogeneous material with ultrasonic inspection do not change the trajectory of motion. With ultrasonic control of metal, rails or seams, the reflection of acoustic waves occurs due to the separation of media with different acoustic resistances. What is important is that the more the acoustic impedances differ, the greater part of all the sound waves will then be reflected and returned to the receiver (when the wave front passes through the interface). Inspection of welds and joints in particular is based on the fact that different inclusions in the metal quite often contain air that has a greater specific acoustic resistance than the metal. As a result, for these inclusion waves hardly pass.
Ultrasonic Flaw Detection
The resolution of the ultrasonic flaw detection method is determined by the length of the sound wave - for an obstacle size less than a quarter of the wavelength, the wave from it is practically not reflected. Radiation of ultrasound is carried out with the help of a special resonator, which converts electric vibrations into acoustic vibrations and introduces them into the material under study. In this case, the reflected signals are converted into electrical signals. They are then registered by measuring circuits.
The variety of the most diverse tasks that arise when it is necessary to carry out measures for the implementation of the ultrasonic method of nondestructive testing has led to the emergence of a number of different ways of such control. Pulsed and resonant methods, as well as methods of acoustic impedance, acoustic emission and free oscillations, have found wide application in modern practice of ultrasonic quality control.
There are at least 5 basic methods for carrying out ultrasonic testing of metal structures: the echo method, the shadow method, the mirror-shadow method, the mirror method, and the delta method. As a rule, modern instruments for ultrasonic flaw detection use several measurement methods in different combinations at once. They form a narrow beam of waves and accurately measure the time that passes from the moment of radiation to the reception of the echo. This allows you to achieve a very high spatial resolution and reliability of the final decision on the degree of defectiveness of a particular part. Complex computerized equipment for ultrasonic testing with effective phased array of radiators makes it possible to obtain extremely convenient for analysis three-dimensional images of defects in the metal. It is worth noting that ultrasound does not damage the part under investigation, and also allows you to carry out all the work very quickly, without significant financial costs and unlike radio-defectoscopy - without danger to human health.