Summary: | Liquefied natural gas (LNG) is liquefied at -162°C at atmospheric pressure and stored in
the inner shell. Due to the transport and storage characteristics of such low temperature
conditions, 9% high nickel steel, which shows excellent strength and toughness even at
low temperatures, is used for the inner wall. On the other hand, the base material of the
inner wall has a tempered martensite structure, whereas the weld metal has an Inconel- based austenite structure with high damping properties in acoustics. Also, the weld metal
is composed of an anisotropic structure completely different from the base material. These
are considered obstacles in non-destructive testing. We applied automated phased array
ultrasonic testing(PAUT) as a replacement of radiographic testing in inspection of LNG
storage tank. To obtain the reference value data, a reference specimen for each thickness
was prepared, and an automatic scanning device was designed and manufactured. Also, a
customized phased array(PA) probe was developed and applied. All parts are integrated
and operated as one system, and the data is analyzed and stored through an operating
program developed in-house. The current system has proven its performance through
field application to a much-improved level in the existing scanning device, probe and
application method. In conclusion, it was proved that our technology can be
commercialized by showing excellent detection ability.
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