gathering acoustic emission information. Acoustic emission
sensors used were PAC R15I of resonant frequency 150 kHz
with an integral pre-amplifier. Fig. 2 shows sensor arrange-
ments for coverage of the repaired tank wall. The row of
sensors was evenly placed at seven different locations by
6 m space along the circumference of the tank wall. The
sensors were attached to the magnetic holders with
couplant. Prior to starting the AE field tests, the sensitivity
of each sensor was measured through three times of pencil
lead breaking on the toluene tank wall, and then the sensors
which deviated by more than ±4 dB from the average value
were recalibrated. The measured average amplitude was
evaluated as 78 dB.
Loading was accomplished by water filling instead of
liquid toluene of 0.87 kg/m 3 density through supply piping
at the top of the storage tank. Acoustic emission testing was
carried out during two loading stages. The first load
sequences consisted of 90% load hold, 90±100% water fill-
ing and 100% hold of maximum operating load. The second
load sequences were 105% hold, 105±110% water filling
and 110% load hold. The water filled at a loading rate of
0.6±0.8 m/h.