Ultrasonic Flaw Detection
We are one of the reputed service providers for Ultrasonic Flaw Detection. In ultrasonic testing, short ultrasonic pulse-waves with center frequencies ranging from 0.1-50 MHz are launched into materials to detect hidden cracks, voids, porosity, and other internal flaws to determine the thickness of the tested object. High frequency sound waves reflect from flaws in predictable ways, producing distinctive echo patterns which can be displayed and recorded by portable instruments. Ultrasonic testing is completely nondestructive, and is widely used in many basic manufacturing, process, and service industries, especially in applications involving welds and structural metals.
Ultrasonic testing works on pulse-echo method. The sound pulse coming from the transmitter is radiated in a beam through a given medium at a specific speed, in a predictable direction, and when they encounter a boundary with a different medium those pulse will be reflected.
The majority of ultrasonic flaw detection applications utilize frequencies between 500 KHz to 10 MHz. At frequencies in the megahertz range, sound energy does not travel efficiently through air or other gasses, but it travels freely through most liquids and common engineering materials.
The speed of a sound wave changes depending on the medium through which it is traveling. Further, affected by the medium's density and elastic properties. In steel the velocity of the sound wave is 6*1000000 mm/sec.
Wavelength is a limiting factor which controls the amount of information that can be derived from the behavior of a wave. In ultrasonic testing, the generally accepted lower limit of detection for a small flaw is one-half wavelength. Waves smaller than that will be invisible. In ultrasonic thickness gauging, the theoretical minimum measurable thickness one wavelength. Wavelength is related to frequency and velocity by the following formula:
w = wavelength
v = sound velocity
f = frequency
Modes of Propagation
Sound waves are propagation of mechanical vibrations. Each particle that vibrates due to an applied excitation oscillates its immediate neighbour and this process continues till total energy transfer occurs. Sound waves in solids can exist in various modes of propagation that are defined by the type of motion involved. Longitudinal waves and shear waves are the most common modes employed in ultrasonic flaw detection. Surface waves and plate waves are also used on occasion.
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