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Title: Fracture mechanics based fatigue assessment of weld toe cracks in offshore tubular structures
Author: Bowness, D.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1997
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Fatigue cracking is currently regarded as the principal cause of damage to ageing offshore jacket structures in the North Sea. The significance of such cracking is usually assessed using fracture mechanics analysis based on in-service inspection data, allowing the operator of the offshore installation to formulate an effective inspection strategy and to effect repair when necessary. A fundamental requirement for a fracture mechanics based fatigue assessment of a tubular joint are suitable stress intensity factor solutions. At present, there are many different sets of solutions in existence which may be applied to tubular joints. Some of these solutions are of limited applicability, and others are based on unsubstantiated assumptions, making the accuracy of any assessment difficult to judge. In this thesis, a thorough review and evaluation of the existing stress intensity factor solutions are reported. To investigate the reliability of the solutions, an accurate three-dimensional numerical modelling procedure for cracked tubular T-joints was developed and used to produce benchmark stress intensity factors. The numerical procedure, which can model doubly curved semi-elliptical weld toe cracks, was also used to conduct a detailed investigation into fatigue crack curvature under the weld toe. The review and evaluation of the existing stress intensity factor solutions highlighted a number of deficiencies in the existing solutions. A parametric study of 3-D T-butts was therefore carried out and new improved solutions proposed. The proposed solutions make physical sense and provide a clear understanding of the effects of the attachment a T-butt. Used in conjunction with the hot spot SCF and DOB, the proposed solutions were also shown to approximate the tubular joint benchmark stress intensity factors well. Fatigue crack growth calculations, performed using the proposed and existing solutions, further illustrate the superiority of the new solutions, which accurately predicted the crack shape development and provided good remaining life estimates.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available