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Title: The assessment of high temperature damage in 2.25 Cr - IMo low alloy steel using ultrasonic techniques
Author: Abdullah, J. B.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1996
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In petrochemical plants and power generating utilities, creep behaviour will affect the service life of components operating at elevated temperatures and stresses. Non-destructive techniques which detect creep damage are therefore important for assessing the remaining service life of the affected components. Whilst various non-destructive techniques have been reported, further studies are necessary to refine and assess the potential of these techniques for quantitative measures to be used for residual life-time prediction. In this thesis, the use of ultrasonic techniques to quantify creep cavitation in 2.25Cr-1Mo low alloy steel was explored. In contrast to conventional methods which only examine surface effects, these approaches should be capable of monitoring both surface and volumetric changes. A computer-based ultrasonic system was developed and testing procedures to characterise the metallurgical variables and creep damage in both ferritic and bainitic 2.25Cr-1Mo steel materials have been established. To evaluate the effects of high temperature exposure to assess microstructural changes and the development of creep damage, a systematic approach with a three-stages experimental work has been undertaken. Firstly, the effects of grain size and phase transformation product on ultrasonic behaviour were evaluated. Samples have been prepared with ferritic and bainitic microstructures. Austenitisation procedures were selected so that samples were produced with average grainsizes in the range 21 to 96 μm. Secondly, ultrasonic techniques were used to characterise microstructural changes due to thermal ageing effects. Materials in ferritic and bainitic microstructures were aged at 700°C for times from 2 to 2000 hours. Thirdly, the assessment of creep damage using ultrasonic techniques was undertaken. This was performed on specimens which had been subjected to creep at various stresses, in a temperature range of 575 to 625°C. In all cases, ultrasonic measurements were supported by optical microscopy, tensile testing and surface hardness measurements to document metallurgical condition.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available