- 1 TWI's Related Projects
- 2 Introduction to Phased Array technology
- 2.1 What are the benefits?
- 2.2 How does it work?
- 2.3 What will it find?
- 2.4 Where is it used?
- 3 Publications
- 4 Phased Array Training Courses
1 TWI's Related Projects
Single Client Project (active) - Phased Array Inspection of Wall to Floor Plate Inner Fillet Weld onto Storage Tank.
Single Client Project (completed) - Phased Array Ultrasonic Inspection of Cracked C-Mn Steel.
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Single Client Project (completed) - Phased Array Inspection of VIT weld.
Single Client Project (completed) - Generic Technical Justification for Ultrasonic Phased Array Inspection.
Collaborative Project (active) - Railect - Development of an ultrasonic technique, sensors, and systems for the volumetric examination of alumino-thermic rail welds.
Group Sponsor Project (active) - 17546 - Reliability of Manually Applied Phased Array Ultrasonic Inspection for Detection and Sizing of Flaws.
Group Sponsor Project (completed) - 14732 - Development of Non-Destructive Techniques for the Detection of Defects in Friction Stir Welds.
Core Research Programme (completed) - 15030 - Validation of Theoretical Models for Focused/Phased Array Ultrasonic Inspection.
2 Introduction to Phased Array technology
2.1 What are the benefits?
The benefits of phased array technology over conventional UT come from its ability to use multiple elements to steer, focus and scan beams with a single transducer assembly. Beam steering, commonly referred to sectorial scanning, can be used for mapping components at appropriate angles. This can greatly simplify the inspection of components with complex geometries. The small footprint of the transducer and the ability to sweep the beam without moving the probe also aids inspection of such components in situations where there is limited access for mechanical scanning. Sectorial scanning is also typically used for weld inspection. The ability to test welds with multiple angles from a single probe greatly increases the probability of detection of anomalies. Electronic focusing permits optimizing the beam shape and size at the expected defect location, thus further optimizing probability of detection. The ability to focus at multiple depths also improves the ability for sizing critical defects for volumetric inspections. Focusing can significantly improve signal-to-noise ratio in challenging applications, and electronic scanning across many groups of elements allows for C-Scan images to be produced very rapidly.
2.2 How does it work?
Phased array systems offer the possibility of performing inspections with ultrasonic beams of various angles and focal lengths using a single array of transducers. Software control over beam angle and focusing is achieved by application of precisely controlled delays to both the emission pulse and received signal for each element in an array of transducers, hence the term "Phased Array" (Figures 1 and 2).
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Fig.1. Beam forming and time delay for pulsing and receiving multiple beams (same phase and amplitude) |
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Fig.2. Beam focusing principle for (a) normal and (b) angled incidences |
While the term 'phased array' implies handling the many signals from multi-element transducers, the resulting A-Scan responses are comparable with those obtained using a fixed angle probe with a conventional pulse-echo imaging system. Therefore, imaging and image interpretation also remain the same as for a conventional pulse-echo system. As with other UT imaging systems, the A-Scan data can be processed to provide top, side and end view images of the inspected volume of material. In addition to standard imaging, Phased Array systems can produce sectorial scans (S-Scans), a feature unique to this technology. S-Scans are real-time side view images generated from a single inspection point without any physical movement of the transducer (Figure 3).
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Fig.3. Typical (a) A-Scan and (b) S-Scan views of a calibration block containing 3mm side drilled holes in a vertical line |
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Fig.4. Electronic scanning with normal beam (virtual probe aperture = 16 elements) |
Multiplexing also allows motionless scanning. In Figure 4, a focused beam is created using 16 elements contained in a Phased Array probe (up to 128). The beam is then multiplexed to the other elements to allow a high speed scan of the component with no transducer movement along that axis. In addition to specifying "individual" pulse-echo probes for an inspection, it is also possible to programme the use of a TOFD pair or a transmit-receive configuration.
Signal to noise is frequently improved with focussed probe techniques of which phased array is one example. Flaw detection and sizing ability is only limited by the beam width which, in theory, can be less than 1mm (0.04"), depending on the excitation frequency. This ability to narrowly focus the beam at a given range provides enhanced spatial resolution of flaw signals with respect to imaging systems that use standard ultrasonic probes. Although the calibration procedure can be complex and time consuming, once completed, scanning speeds of up to 100mm (4") per second can be achieved.
2.3 What will it find?
Manufacturing flaws (lack of sidewall fusion, lack of root penetration, lack of root fusion, porosity, etc.), in-service flaws (fatigue cracking, stress corrosion cracking, corrosion, erosion, etc.) and parent material flaws (inclusions and laminations).
2.4 Where is it used?
Ultrasonic phased array systems can potentially be employed in almost any test where conventional ultrasonic flaw detectors have traditionally been used. The most important applications are weld inspection and crack detection across a wide range of industries including aerospace, power generation, petrochemical, metal billet and tubular good suppliers, pipeline construction and maintenance, structure metals, and general manufacturing. Phased array can also be effectively used to profile remaining wall thickness in corrosion survey applications.
3 Publications
Introduction to Phased Array Ultrasonic Technology Applications
New developments of ultrasound phased array for the evaluation of friction stir welds
Phased array scanning of artificial and impact damage in carbon fibre reinforced plastic (CFRP)
Ultrasonic phased array inspection of FSW lap joints
Independent qualification of phased array inspection of fillet welds
Correlation of phased array inspection and fatigue performance of FSW joints
Ultrasonic phased array inspection technology for the evaluation of friction stir welds
Signal processing for quality assurance in friction stir welds
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