PHASED ARRAY ULTRASONIC TECHNIQUE Phased Array Ultrasonic Testing (PAUT) is an advanced nondestructive examination technique that utilizes a set of ultrasonic testing (UT) probes made up of numerous small elements, each of which is pulsed individually with computer-calculated timing. This technique can be used to inspect more complex geometries that are difficult and much slower to inspect with single probes. PAUT can be used to inspect almost any material where traditional UT methods have been utilized, and is often used for weld inspections and crack detection
Compared to other forms of UT, PAUT has several advantages. PAUT can be conducted more quickly than other forms of UT, often within a fraction of a second. It can easily be used for repeat scans because it has a high degree of repeatability. By emitting beams of multiple different angles sequentially, PAUT is able to create detailed and accurate cross-sections of a part. It is also particularly useful in situations where there is less room for mechanical scanning because it's able to sweep the beam without moving the probe.
Eddy current arrays (ECA) are the natural extension of ECT. ECAs are composed of arrays of coils that activate in sequences intended to eliminate interference between them. The array slides on top of surfaces, offering an overall wider coverage and better sensitivity to defects than conventional ECT. ECA technology can detect surface-breaking defects and, to some extent, subsurface defects. ECA probes can also be shaped to match more "exotic" geometries, which enable single-pass scanning of geometries that traditionally pose serious challenges to other inspection technologies.ECA technology is used as an alternative to other surface inspection technologies in such industries as the oil, gas, and petrochemical industry; the power generation and nuclear industries; the aerospace industry; and the heavy equipment and mining industries. ECAs also very successfully supplement ultrasonic testing (UT) and phased-array UT because these suffer from what is often referred to as a "dead zone" near the surface, making it difficult for them to detect near-surface defects.
Therefore, surface applications of ECA technology are numerous, ranging from weld inspection on pressure vessels and pipes..
TOFD is usually performed using longitudinal waves as the primary detection method. Ultrasonic sensors are placed on each side of the weld. One sensor sends the ultrasonic beam into the material and the other sensor receives reflected and diffracted ultrasound from anomalies and geometric reflectors. TOFD provides a wide area of coverage with a single beam by exploiting ultrasonic beam spread theory inside the wedge and the inspected material. When the beam comes in contact with the tip of a flaw, or crack, diffracted energy is cast in all directions. Measuring the time of flight of the diffracted beams enables accurate and reliable flaw detection and sizing, even if the crack is off-oriented to the intial beam direction. During typical TOFD inspections, A-scans are collected and used to create B-scan (side view) images of the weld. Analysis is done on the acquisition unit or in post-analysis software, positioning cursors to measure the length and through-wall height of flaws
TOFD offers rapid weld inspection with excellent flaw detection and sizing capacities. The diffraction technique provides critical sizing capability with relative indifference to bevel angle or flaw orientation. TOFD can be utilized on its own or in conjunction with other NDT techniques.
