TOFD (Time of Flight Diffraction)
PA (Phased Array)
Automation of welding systems is among the main drivers of development of contemporary non-destructive testing, as a prerequisite for increasing the work rate and output while at the same time improving the efficiency and defect detection precision. These technologies are mainly used in the nuclear energy industry, construction of long-distance pipelines, vessels or steel structures in the refining industry.
The TOFD (Time-Of-Flight Diffraction) method uses diffraction of ultrasonic waves. The test records ultrasonic wave pulses distributed on the edges of material defects. The basis of the measuring system are two broadband longitudinal wave angle beam probes positioned at a fixed distance from each other. One of the probes is a transmitter and the other one is a receiver. Defects are located on the basis of the time of flight of the ultrasonic wave, while defect size is measured on the basis of the differences of the time of flight from one edge of the defect to another.
Advantages of the TOFD method:
Very high limit of detection for planar discontinuities;
Precise location of material defect (significantly higher accuracy than that of the pulse-echo method);
High testing resolution with reading data in the range of 0.1 mm;
High reliability of test results.
The PA (Phased Array) method is an extension of the traditional pulse-echo ultrasound testing. Multiple transducers in an array inside the testing probe are used in the PA method for controlling the ultrasonic beam so as to obtain an image similar to a radiography image. Compared to conventional techniques, PA tests are faster, more reliable, with a higher resolution and sensitivity, which improves the test quality.
TOFD and PA tests are carried out with Olympus OMNISCAN X3.
Digital ultrasonic testing is performed in conformity with the following standards:
PN-EN ISO 10863:2020-12 - Non-destructive testing of welds — Ultrasonic testing — Use of time-of-flight diffraction technique (TOFD)
PN-EN ISO 15626:2018-10 - Non-destructive testing of welds — Time-of-flight diffraction technique (TOFD) — Acceptance levels
PN-EN ISO 13588:2019-04 - Non-destructive testing of welds — Ultrasonic testing — Use of automated phased array technology
PN-EN ISO 19285:2017-11 - Non-destructive testing of welds — Phased array ultrasonic testing (PAUT) — Acceptance levels
