A study on distinguishing techniques between lamination and corrosive thinning of potentially dangerous equipment

• Main Authors: Yi-shen Lin, 林益生
• Other Authors: Chih- Ju G.Jou
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/15802303761289151331

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.