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Title: The effect of specimen geometry and hoop stress on the high temperature behaviour of ½ Cr ½ Mo ¼ V/2 ¼ Cr/Mo steel
Author: Hollinshead, P. M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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Current research into the creep behaviour of welded steel pipes is undertaken in the axial stress direction, and the sample geometries vary greatly. Moreover, for a pipe acted on solely by internal steam pressure, the hoop stress is approximately twice the axial stress. This research programme aimed to find the effect of variations in sample geometry and position of manufacture upon the creep properties of uniaxial specimens, and also the effect of hoop stresses on the creep behaviour and microstructure of a weldment. Ex-service weldments were employed for the majority of the research, however, a new weldment was fabricated using standard welding techniques. Uniaxial specimens of varying geometries were manufactured from ex-service material. Samples with their heat affected zones (HAZ) parallel to the loading direction (parallel weld specimens) were fabricated from both new and ex-service weldments. Creep tests were undertaken on uniaxial and parallel weld specimens. The latter, when loaded, simulated the effect of the hoop stress. Selected parallel weld samples were interrupted during testing, and metallographically examined. Uniaxial specimens manufactured from the weld root failed in a TYPE IV manner. Samples made from the outer edge of the weldment failed in the weld metal. Uniaxial specimens with a cross section or diameter of less than or equal to 7mm showed reduced creep lives. Under identical test conditions, parallel weld specimens showed better creep properties than weld metal samples, but poorer properties than base metal samples. In the parallel weld samples, weaker materials off-load stress onto the stronger materials. Initially, all of the stress was on the coarse grain HAZ, which failed after ~14% of creep life, off-loading all of the stress onto the base metal. This failed after ~94% of the creep life, off-loading the stress onto the weaker materials, which quickly fail.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available