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Technical Discussions
David Mackintosh
Engineering,
Acuren Group Inc., Canada, Joined Feb 2011, 85

David Mackintosh

Engineering,
Acuren Group Inc.,
Canada,
Joined Feb 2011
85
22:10 Mar-24-2010
Phased array still on the learning curve

The colour display makes phased array a breeze. If there's a red spot there's a defect, right?

Wrong.

This isn't like point-and-shoot digital cameras replacing point-and-shoot film cameras. Phased array is a whole new level of complexity.

Many beginner technicians are quite capable of setting up the phased array equipment, calibrating it, scanning the weld, and analyzing the data while being unaware that the beam missed the weld root entirely. In other words, more channels, more data, more computational power, more pitfalls.

Because of the number of parameters, consistency in phased array is hard to achieve. Currently the best tactic is to depend on competent, trained, and experienced phased array technicians who have demonstrated their aptitude on test pieces.

Some parameters under discussion include:
- Probe offset from weld for line scans.
- Depth of focus.
- Type of calibration flaw.
- Angle of incidence of the beam on the weld fusion face.
- Density of digitization points in the examination volume.

The values chosen for these parameters generally vary from technician to technician or in some cases will be ignored completely. Even the experts are having trouble: one wrote that "results showed that defect detection was difficult to predict, and depended on defect location and angle, plus array location and component thickness." (www.iiw-iis.org/iiw/extranet/static/MS/C-V/V-1407-08/C5-Codes-Rev-6.pdf)

If I was an owner, I would definitely use phased array wherever possible, but I would require a simple performance demonstration for technicians coming on site, no more than 4 hours or so.

Even then there’s a lot of research to do. Has anyone seen any papers comparing rastered phased array with scanned phased array with conventional UT?

David

 
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