What is Ultrasonic Testing?
Ultrasonic testing (UT) Characterised a range of non-destructive testing (NDT) techniques that send ultrasonic waves through an object or material. These high frequency sound waves are transmitted into materials to characterise the material or for flaw detecting
Where Is Ultrasonic Testing Used?
The basic principle of ultrasonic testing is the use of sound to inspect a material’s thickness at different points.
Ultrasonic thickness measurements can help inspectors find defects such as tiny cracks, gaps, corrosion, or other flaws in materials that are too minute to be seen by other NDT methods. It can also be used to find corrosion—if one area is thinner than another, that could be a sign that the area has been corroded
In addition to metal, an ultrasonic thickness test can be used to test plastics, composites, and ceramics. It can also be used to test concrete but the findings may not be as reliable.
Her are the industries that commonly use ultrasonic testing as part of their inspection procedures:
- Aerospace
- Automotive
- Metals & Casting
- Oil and Gas
- Power Generation
Use of couplant in ultrasonic testing
The couplant displaces the air and makes it possible to get more sound energy into the test specimen so that a usable ultrasonic signal can be obtained. In contact ultrasonic testing a thin film of oil, glycerin or water is generally used
Explain dead zone, near zone and far zone
Dead zone– The dead zone comprises the distance between the front face of the transducer and the echo. The standard tests will not record any flaws within this area. This is one of the common disadvantages to ultrasonic sensors.
Near Zone– Near zone is the zone where the sound wave pressures at each point is not uniform as every particles in the crystal generates sound waves.
Far zone:- Far zone length is the region of the beam that increases diameter with the distance from the transducer and smooth decrease of sound energy. The region that lies beyond a distance of one near zone length, where the beam diameter is increase. Also called Far zone, Far field, Fraunhofer zone.
What are the Advantages and Disadvantages of Ultrasonic Testing?
Advantages of Ultrasonic Testing
- High sensitivity, allowing identification of very small flaws
- More accurate than non-destructive techniques in determining the thicknesses of parallel surfaces and how deep internal flaws are.
- High penetrating power for easy detection of flaws in deep parts
- Has the ability to estimate the shape, size, orientation, and nature of defects.
- Has no adverse effects on equipment and materials used
- Ability to estimate the structure of compound constituents with different acoustic features
- Non-hazardous to operators or any nearby personnel
- Best of portable or automated activities
Disadvantages of Ultrasonic Testing
- Parts that are irregular in shape, rough, very thin or small, or not uniform are not easy to inspect
- The surface of the test material must be prepared by removing loose scale, cleaning, paint, etc., but paint well bonded to the surface should not be removed
- Inspected objects or materials should be water-resistant if you use water-based couplants that lack rust inhibitors. Antifreeze fluids with inhibitors are best
- Manual operations should be carried with a skilled technician’s attention. The transducers alert to both tolerable anomalies of specimens (termed “noise”), the normal structure of some objects, and serious flaws that could compromise the integrity of the specimen. These signals should be inspected by experienced technicians able to follow up with other testing methods such as non-destructive methods
- Couplants are used to offer effective transmission of ultrasonic wave energy between the parts being inspected and the transducers unless when using a non-contact method. Non-contact methods include Electro-Magnetic Acoustic Transducers and Laser.