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Title:	Reliability of ultrasonic technique in thickness measurement for corrosion monitoring
Authors:	Elsyed Yassir Yassen. (P37576)
Supervisor:	Abdul Razak Daud, Prof. Dr.
Keywords:	Corrosion and anti-corrosives. Ultrasonic techniques
Issue Date:	12-Jan-2012
Description:	Corrosion monitoring is one of the main agenda in the operation of the industrial plants because corrosion can create economic losses as well as affecting safety aspects of the plants. One of the most widely applied techniques for corrosion monitoring is thickness measurement by ultrasonic technique. The main advantages of this technique are that it is not required to access both sides of the structures to make the measurements, besides small probes and data reading devices are commercially available. However, the reliability of the measurement results has become an important issue to Non-Destructive Testing (NDT) users. The accuracy of measurement of thickness reduction due to corrosion will allow plant engineers to take appropriate and efficient actions on corrosion control. The aim of this study is to evaluate the accuracy of the ultrasonic pulse-echo techniques in thickness measurement for corrosion monitoring. Two types of digital ultrasonic equipment were used, i.e. ultrasonic thickness gauge and ultrasonic flaw detector. Ten groups of carbon steel samples, five samples in each group were prepared. The samples were then exposed to dilute sulphuric acid solution for different exposure times in order to produce samples with different thickness loss due to corrosion. The thickness of the corroded samples was measured using the ultrasonic techniques and micrometer. Micrometer measurement was taken as reference and considered as accurate for the purpose of evaluating the accuracy of thickness measurement by the ultrasonic techniques through comparison of thickness data obtained. The comparison was performed by fitting the mean value of readings obtained by the two measurement techniques to a straight line using bivariate least squares where y-axis is for thickness data obtained by ultrasonic technique and x-axis is for thickness data obtained by micrometer. If the ultrasonic technique has a good accuracy then the intercept of the straight line on y-axis and the slope should not be significantly different from 0 mm and 1 respectively. The values of the intercept and the slope for the thickness gauge are 0.0165 mm and 1.0022, respectively, and for the flaw detector with dual element probe are 0.0120 mm and 1.0444, respectively. While for the single element-single echo flaw detector are -0.003 mm and 1.0441, respectively, and for the single element-multiple echoes flaw detector are -0.0024 mm and 1.0004, respectively. A statistical test was applied at the 5% significant level, to compare the obtained intercept and slope values with their respective theoretical values. The results showed that for thickness losses measurement between 0.20 and 2.20 mm, the mean readings provided by the thickness gauge are relatively free from systematic error. The ultrasonic thickness gauge gives a relatively accurate mean measurement. The mean measurements produced by the flaw detector with dual element and by the single element-single echo flaw detector have 4% proportional systematic error. The ultrasonic flaw detector produces a less accurate mean measurement. However, the single element-multiple echoes flaw detector gives accurate mean measurements because it is relatively free from systematic error. The accuracy of ultrasonic flaw detector measurement could be improved by using single element probe with multiple echoes measurement mode.,Master
Pages:	122
Call Number:	TA418.74 .E457 2012
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

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