Ultrasonic Testing (UT)

Used to locate surface and subsurface defects in metals, fabrication, steel products, plastics, wood etc. Ultrasonic inspection is also used to measure the thickness of materials and characterize properties of material based on sound velocity and attenuation measurements

It is also used in the detection of inter laminar separations and regions that have been improperly processed or damaged in layered composite structures

The most commonly used ultrasonic testing technique is pulse echo, whereby sound is introduced into a test object and reflections (echoes) from internal imperfections or the part's geometrical surfaces are returned to a receiver

Advantages

• • Depth of penetration for flaw detection or measurement is superior to other methods.
• • In general access to only one surface is required.
• • Results are generated instantly with little or no processing time
• • Highly portable equipment, which is well suited to field inspection and in-service inspection
• • Minimum part preparation is required.
• • Application to a broad range of materials
• • Method can be used for much more than just flaw detection

Limitations

• • Surface must be accessible to probe and Couplant.
• • Skill and training required is more extensive than other technique.
• • Surface finish and roughness can interfere with inspection.
• • Thin parts may be difficult to inspect.
• • Linear defects oriented parallel to the sound beam can go undetected.
• • Reference standards are often needed
• • Less effective in highly inhomogeneous and coarse- grained materials

TOFD (Time of Flight Diffraction)

The TOFD (Time of Flight Diffraction) technique is a computerized and automated system for weld inspection which is able to scan, store, and evaluate indications in terms of height, length, and position with a grade of accuracy never achieved by other ultrasonic techniques.

TOFD has two blind zones where it is not sensitive to defects; hence TOFD needs to be supplemented by a conventional pulse-echo examination of the near and far walls



   

Phased Array UT

Phased array can successfully overcome many of the inconsistencies of the manual application. Phased array probe is constructed from a number of very small elements arranged in a line or in a specific cluster design. By activating a number of the elements at once and applying specific voltages to each element a predetermined beam angle, or beam of varying angles can be produced. Furthermore, by moving the active elements along the probe the beam is moved forward/backward in a manner similar to the movement of a manual technique.

When the phased array wedge is placed on the parent material at a specific standoff position and moved along the weld, data can be collected and imaged as a C-scan (plan view) of the weld, much like a traditional radiograph. To compliment this, the ultrasonic imaging system can also show the A-scan, B-scan (end view), D-scan (side view) and in the case of a beam with varying angles S-scan (or sectorial scan).