NVI technicians can view indications using a variety of advanced ultrasonic configurations. These include B-scans, C-scans, and S-scans as well as the time of flight diffraction and guided long-range. Different scan groups are conducted at a single time, and the process can be automated using mechanized scanners.
These technologies have recently been incorporated into industry codes. This is an exciting development because they create possibilities for testing in situations where traditional methods can be used only with difficulty.
- Automated Ultrasonic Testing (AUT)
Automated Ultrasonic Testing is a method that uses scanners that travel around the weld to indicate and map out the location, size, and shape of the present flaws or corrosion areas. While the scanner is in motion, the scans become visible on a computer inside of the truck for review on the spot. NVI uses automated systems to test components while they are in service. They can be accomplished using crawlers, robotic vehicles, or track systems. The advantages of this technology include speed, accuracy, and broad area coverage.
- Guided Long-Range
Guided Ultrasonic Long-Range testing is used to scan a large volume of pipe to detect areas that may have some metal loss. To identify the problem areas, a transducer and a collar are placed around the pipe. The transducer, controlled by a computer, will shoot low-frequency sound waves 360 degrees around the pipe wall and down the pipe in both directions from the source. This remotely operated screening technique is used to identify damage mechanisms occurring both internally and externally such as leaks, corrosion, erosion, cracks, dents, etc. Once a flaw is discovered, it is recorded. This method allows for a reduction in overall inspection and insulation costs. NVI uses it to inspect inaccessible areas such as road crossing as well as for straight runs of pipe over long distances. It is approved by the Pipeline and Hazardous Materials Safety Administration.
- Phased Array
The phased array transducer consists of multiple aligned transducers (elements). Each element is pulsed individually to create various angles. As a result, the beam from a phased array probe can be moved (rastered) electronically (E-Scan) and focused, without moving the probe. The beam can be swept through many angles at the same time (S-Scan) and each angle focused at a specific depth. Weld flaw detection is the primary application; however NVI uses phased array for wall-thickness measurements and corrosion detection. Because it is safe to be used alongside other crafts, phased array is good alternative to radiography. A primary advantage is, like radiography, phased array provides a permanent electronic record for review/auditing of results.
- Time-of-Flight Diffraction (TOFD)
Compared to traditional ultrasonic testing, time of flight diffraction is a sensitive and precise method for crack detection and measurement. It is validated to be one of the most effective techniques for locating and sizing discontinuities in ferritic welds. In a time-of-flight diffraction system, a pair of ultrasonic probes is placed on opposite sides of a weld. The transmitting probe emits an ultrasonic pulse that is picked up by the receiver probe. When a crack is present, the ultrasonic wave diffracts at the crack tip. NVI technicians use the measured time of flight of the pulse to calculate its depth.
- B- Scan and C-Scan
A B-scan image is produced when ultrasonic inspection is plotted along a cross-sectional view of a component. It is often observed for an individual scan line, allowing through wall sizing of indications. A C-scan image is produced when ultrasonic inspection is plotted on a “plan view” of a component. It can be used to show changes in wall thickness or the extent of corrosion in an area.