Phased Array

Ultrasonic phased arrays are a novel technique for generating, receiving and imaging ultrasound. Instead of a single transducer and beam, phased arrays use multiple ultrasonic elements and electronic time delays to create beams by constructive and destructive interference. As such, phased arrays offer significant technical advantages for weld testing and plant monitoring over conventional ultrasonics as the phased array beams can be steered, scanned, swept and focused electronically from a fixed probe position. Beam steering permits the selected beam angles to be optimized ultrasonically by orienting or focussing them perpendicular to the predicted discontinuities, for example lack of fusion in automated weld inspections.

 

Advantages of Ultrasonic Phased Arrays

    • Phased arrays allow real-time control of three important ultrasonic probe parameters
      • Focal distance: continuously and dynamically adjustable
      • Beam angle: continuously and dynamically adjustable
      • Focal spot size: dynamically adjustable
    • Extra benefit
      • Multiplexing allows fast displacement of ultrasonic beam within probe
    • Main benefits of ultrasonic phased arrays
      • High-speed inspection using single-axis scans instead of conventional raster scan
      • Near-optimal focal length and focal spot for various areas of complex parts or thick components
      • Small, simple probe assembly with multiple beams from a single probe
      • Easy-to-install, one-axis scanning systems
      • Better detection in austenitic materials and dissimilar metal (DM) welds
      • Alternative to Radiographic imaging.

 

TOFD (Time of Flight Diffraction)

TOFD and its principles are well documented. Utilizing diffracted energy in the detection of flaws, the technique is less reliant on flaw orientation and morphology than standard pulse echo techniques, leading to improved sizing and probability of defect detection (POD). Additionally, computerized electronic data capture and storage, in conjunction with scanning manipulators enable rapid scanning speeds to be achieved TOFD has now been accepted as an alternative to Radiography in Pre-Service Inspections with standards such as ASME 2235, and its use in pipe weld and thick walled pressure vessel fabrication is now common place.

Due to it’s sensitivity and sizing accuracy, TOFD is also an excellent tool for in-service material and flaw monitoring. Engineers who are monitoring root erosion, stress corrosion cracking, vessel cladding, Hydrogen Attack, Weld and Steam Chest cracks for example, are all now utilizing TOFD as part of an ongoing inspection regime.

Integrity NDT personnel have over 10 years of experience in planning, managing and carrying out TOFD on pre-service and in-service projects, around the globe. We can advise and develop TOFD procedures and have developed specialist scanning equipment for carrying out inspections.

Method:

-British Standard 7706: Calibration and setting-up of the ultrasonic time-of-flight-diffraction (TOFD) technique for the detection, location and sizing of flaws
-ENV 583 pt6: Non Destructive Testing – Ultrasonic Examination – Part 6: Time-of-flight diffraction technique as a method for detection and sizing of discontinuities spection

Technique Specification:

-PrCEN/TS 14751: Welding – Use of time-of-flight diffraction technique (TOFD) for examination of welds
-Code Case 2235: Case of ASME Boiler and Pressure vessel code Section I and Section VIII, Divisions 1 and 2, Use of Ultrasonic examination in Lieu of Radiography

 

Acceptance Criteria:

· Code Case 2235: Case of ASME Boiler and Pressure vessel code Section I and Section VIII, Divisions 1 and 2, use of Ultrasonic examination in Lieu of Radiography
· prEN 15617: Acceptance criteria for the Time of Flight Diffraction inspection technique (European Standard)