NDE Associates offers the following services for Phased Array inspections
Phased Array for Weld Inspections
Phased Array of Complex Components
Phased Array for Defect Sizing
Phased Array in Lieu of Radiography
Phased array technology offers an attractive option to perform UT in lieu of radiography. This main advantage being that phased array inspection does not interfere with surrounding work. Radiography requires barricading a perimeter during the exposures.
Why use Ultrasonic Phased Arrays ?
Unlike conventional and automated ultrasonic testing, which is performed for fixed angles of 45, 60 and 70 degrees, phased array testing can cover all angles in this range. This is significant as a single phased array inspection can cover all angles from 40 to 75 degrees and displays the image in real time. The real time image is direct superimposition of the ultrasonic illumination on the test piece and is easy to interpret. Using swept angle S-scans, PAUT requires smaller surface distance for inspection compared to AUT or manual UT. PAUT can cover a large cross-section of the test piece from a single probe location. On the contrary, AUT either requires raster scanning or multiple probes placed over a range of surface distance to cover the entire cross-section of the test piece. When properly used, phased arrays can be used on all ultrasonic applications and result in a highly reliable NDT inspection.
Phased Array Tests on Weld flaws
We have tested the capability of phased arrays for detection of defects in weld test samples. These samples include plate and pipe sections. Weld flaws in these samples include toe cracks, center line crack, LOF, LOP, slag and porosity. Tests were conducted using two different systems. Test results showed that both systems successfully detected all the defect types. Defects were definitely easy to detect and interpret with the phased arrays compared to the conventional A-Scan machine proving the reliability of phased arrays for weld inspection. For further reading see "Ultrasonic Phased Arrays for Weld Testing", Paper Copyright by Materials Evaluation, ASNT, Columbus, Ohio.
Phased Array Testing of Butter Welds
Butter welds are commonly used for subsea applications. These can include
both carbon steel and A625 butter welds. The most common flaw in butter
welds is lack of fusion (LOF) between the beads. These welds can be easily inspected
using phased arrays. The inspection is done by scanning a PAUT probe from the ID surface of the pipe.
Refracted shear waves are used for carbon steel butter welds and A625 welds
are inspected using refracted L-waves. L-waves are also used when the ID has
a A625 clad. The
technique reliably detects flaws in butter welds.
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| PAUT Inspection Technique. The probe mounted on a radiused wedge is scanned from the pipe ID surface. | Indications detected by PAUT in butter welds verified by Liquid Penetrant Testing |
Crack sizing with Phased Arrays.
Accurate sizing of flaws requires a
small focal spot size at the defect location. The three figures above show
improvement in sizing with increased probe aperture: 12 mm, 18 mm and 24 mm.
Probe frequency is 5MHz. Accurate flaw sizing requires probes with
high frequencies and large apertures. As a rule of thumb for flaw sizing,
the phased
array active aperture should at least be 0.4 times the part thickness and a
preferred frequency of 5 MHz. Therefore, to inspect a 2 inch (50 mm) plate,
the active aperture of the probe should be at least 20 mm. Smaller probes will result is large beam spread and
over sizing sizing of flaws.
(Note: Active aperture is the element size x no. of elements that are
active, eg: a probe with sixteen 0.75 mm elements has a active aperture of
12 mm. In case, only 12 consecutive elements are used, the active aperture
drops to 9 mm )
Improvement in Flaw Sizing with increased PA Aperture (Top Left) Root Crack
- 3 mm (0.120") (Top right) 5 MHz, 12 mm aperture. Flaw shown by dark
black lines is oversized to almost double its size. (Bottom left) 5 MHz, 12
mm aperture. (Bottom right) 5 MHz, 24 mm aperture. Flaw correctly sized.
See also PA Technology
"Ultrasonic
Phased Arrays for Weld Testing",
Paper Copyright by Materials Evaluation, ASNT, Columbus, Ohio.
ID Crack detected on 0.5 inch thick
plate vee weld.
LOF detected on 0.5 inch thick 8 inch dia pipe.
Inspection of Turbine Steam Chest for thermal fatigue cracking. Instrument:
Phasor
NDE Associates, Inc.
515 Tristar Drive
Webster, TX 77598
Phone: 281-488-8944 Fax: 281-488-8485
