FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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V = f* - 0.9
ak
N [2]
h. /^k)7__i
N " l N / \1+ I
It ^[ 1 + (1 -^'
(Deviation + 5%)
(Deviation + 3%)
(Deviation + 5%)
Ultrasonic theory also shows that the beam diameter within the acoustic
focal range can be given approximately by:
where fa^ = acoustic focus (note f ,/N = focusing factor, Z)
fopt = optical focus
Lg = the 6 dB working range
AL = the part of L distributed before f ak
V = gain (increase in sensitivity)
N = transducer nearfield length
The theory is relatively easy to apply, and focused beams can be readily
reproduced (6,7) to meet the various inspection requirements.
Weld Specimens
The pipe specimens were in a range of sizes (610 mm diameter x 6.7 mm wall,
to 1067 mm diameter x 15 mm wall thickness) typical of what is being used
in the field. They were fabricated using gas-metal-arc (one sample) and
shielded-metal-arc (seven samples) welding processes with representative
beveled joint specifications. Defects were manually introduced by the
operator during the welding process and included: inadequate penetrations,
incomplete root fusions, lack of sidewall fusions, internal undercuts, slag
inclusions (wagon tracks) and root cracks. They ranged in size from over
50% wall thickness (root cracks) to a few millimetres (slag inclusions).
Radiographic inspection carried out prior to ultrasonic inspection detected
all but one of the manufactured defects (incomplete root fusion), but could
give little information concerning defect sizes.
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