How Does Ultrasonic Testing Work?
What Is UT Non Destructive Testing?
Ultrasonic Non Destructive Testing (UT) comprises a range of non destructive testing methods that use ultrasonic waves to test for flaws both internal and external in a material or object. High frequency sound waves are passed through the material which are then picked up to map out the structure of said material, including any flaws or discontinuities. The majority of ultrasonic NDT inspections utilise short pulse waves with frequencies ranging from 0.1-1.5 MHz, though in some cases pulse waves with frequencies as high as 50MHz can be used. Ultrasonic testing is an ideal method for non destructive testing, as it can test and map out the internal structure of an object rather than just find surface defects, and causes absolutely zero damage to said object. Ultrasonic non destructive testing has many applications in the welding and fabrications industry, one of the most common is thickness testing, which is used to detect the thickness of an object when assessing pipework for corrosion. Alongside this, periodic inspections can take place to test for corrosion in an object as well as the growth of known flaws. It is commonly used in such industries as construction, manufacturing, automotive, aerospace, metallurgy & medical.
How Does Ultrasonic Testing Work?
Ultrasonic NDT works by using a piezoelectric transducer, connected to some kind of flaw detector, which often on a basic level comprises a pulser receiver and some form of display. This transducer is then passed over the object, using a couplant which is required to transmit the energy from the transducers sound waves efficiently into the object. The couplant is usually made up of oil, gel, or water. However, in non contact testing techniques such as laser excitation or using an electromagnetic acoustic transducer, this couplant is not required. With pulse echo testing, the transducer both emits and receives the energy generated from the sound wave. During ultrasonic weld inspection, a strong specular reflection is required to resolve a flaw response from the background noise level with pulse echo ultrasonics. For planar flaws such as cracks and lack of fusion, a specular reflection will only happen if the ultrasonic beam is 90 degree angle to the plane of the flaw. Shear wave probes with an angled beam are commonly used for the manual ultrasonic inspection of welds in ferritic steels, as these provide the only way of directing ultrasound into the weld body when the cap reinforcement is still present. Where a weld cap restricts probe movement, the sound can be reflected off the bottom surface and directed into the weld body under the cap. Where soundwaves are emitted at a direct angle to the area of interest, this is referred to as “half skip testing”. “Full skip” testing occurs when the bottom surface is used to reflect the sound before it enters the weld. Typically, for a girth weld, a 45° probe is used for inspecting the root region, and 60°/70° probes for the sidewall fusion faces and weld body. The behaviour of the echo-dynamic pattern and shape of the flaw response (with respect to probe movement) can be used to identify the type of flaw, as well as estimating the length and sometimes the through-wall height of the flaw.
Advantages Of The Non Destructive Testing Ultrasonic Method
There are many advantages for using the ultrasonic non destructive testing method. Some of these include its high penetration power, meaning it is able to detect flaws deep within an object rather than just on the surface, along with its high sensitivity, which allows it to detect very small flaws in said object. It can also be used to test an object when only one side of the object is accessible to the tester, and is often a lot more accurate than other non destructive testing methods. Results are available immediately, making it one of the fastest non destructive testing techniques around, and it is non-hazardous to humans and the environment. For more information on Ultrasonic Non Destructive Testing and how it can be used both onsite and offsite, contact SureCheck NDT today.