Summary: | 碩士 === 國立高雄第一科技大學 === 環境與安全衛生工程所 === 94 === Abstract
Ultrasound thickness measurement is the most fundamental check item provided
by the regulations of potentially dangerous equipment. Therefore, the measurement of
thickness can let us understand if situations of corrosive thinning or degradation exist,
and ensure the safety of equipment operation. However, the production of steel plate is
usually accompanied by the occurrence of lamination, and this phenomenon will result
in the reducing of thickness measurement, misleading that material thinning exceeds the
acceptable thickness and therefore influencing the enterprises very much for
replacement of that equipment or production losses due to emergency shut-down.
Because the current technique of Method of Straight-Beam Ultrasonic Test provided by
CNS is only aimed at lamination test of newly-made materials; moreover, in practice,
the signals of corrosive thinning are easily mixed up with lamination judgment of
materials in use with Straight-Beam Ultrasonic Test, making it hard for inspectors to tell
from. lamination or corrosive thinning. Therefore, in practice, a set of appraisal methods
is urgently needed to distinguish between corrosive thinning of materials in use and
phenomena of lamination.
This study uses ultrasound broad-band probe to induce broad-band ultrasound and
to make sure whether it is corrosive thinning or lamination by the frequency response of
the back echo and indicative echo to attain the goal of distinguishing lamination from
corrosive thinning. In this study, we aims at natural defects with lamination and
corrosive thinning to conduct the tests and the result are concluded as follows: When the
lamination and the back echo both exist, the response of lamination echo in high
frequency is greater than the back echo; when there exists only the lamination echo, the
frequency response of lamination echo is similar to that of echo in sound area. And the
frequency response of test pieces with corrosive thinning is opposite to results when
lamination exists. Making use of the above-mentioned method of frequency response of
echo, lamination and corrosive thinning can be distinguished apart.
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