GE 37 400, Technical Reference And Operating Manual

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Rating of welds (function group AWS D1.1) 5 Operation
USM 36 Issue 2 (12/2013) 5-41
Rating of welds according to AWS D1.1
The rating of defects in welds according to the specifica-
tion AWS D1.1 is based on an evaluation of the signal
amplitude. In this method, the echo amplitude of the flaw
echo is compared with the echo amplitude of a known
reference reflector. In addition, the sound attenuation in
the test object is also taken into account.
The result is a dB value which is called flaw class. The
flaw class D is calculated according to the formula:
D = A – B – C
with:
● A = flaw gain (in dB)
Absolute instrument gain with which the maximum
flaw echo is at 50 % (±5 %) echo height.
● B = reference gain (in dB)
Absolute instrument gain with which the maximum
reference echo (e.g. the 1.5 mm side-drilled hole
from the reference standard V1 or IIW type 1 or 2) is
at 50 % (±5 %) echo height.
● C = sound attenuation factor (in dB)
The value is calculated according to the formula:
C = 0.079 dB/mm • (s – 25.4 mm), with s = sound
path of the flaw echo.
The sound attenuation correction is calculated and
displayed automatically by the instrument. The value
is set to zero for sound paths smaller than or equal to
25.4 mm (1 inch).
● D = flaw class (in dB)
This is the result of the evaluation according to AWS.
The calculation is made in the USM 36 according to
the above-mentioned formula.