Effects of weld strength mismatch on crack driving forces for circumferential surface crack in pipes under bending
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Fracture assessment for circumferential surface cracked weld pipes play an important role in current applications of fitness for service (FFS) procedures for the safety assessment of critical welded structures. These crack-like defects are most often formed during in service operation and exposure to aggressive environment (such as, for example, stress corrosion assisted cracks) or during welding fabrication. Structural components falling into this category include girth welds made in field conditions for deep water steel catenary risers. More efficient and faster installation methods for these structures now underway employ the pipe reeling process which allows welding and inspection to be conducted at on-shore facilities. The welded pipe is coiled around a large diameter reel on a vessel and then unreeled, straightened and finally deployed to the sea floor. However, the reeling process subjects the pipe to high levels of bending loads and plastic deformation with potential impact on crack propagation of undetected (circumferential) flaws at girth welds. This work focuses on the applicability of the evaluation procedure to determine the elasticplastic J-integral and CTOD for weld pipes with circumferential surface cracks subjected to bending load for a wide range of crack geometries and overmatch levels based upon EPRI framework. The extensive nonlinear, 3-D numerical analysis provide a definite full set of solutions for J and CTOD which enters directly into fitness for service (FFS) analyses and defect assessment procedures of cracked pipes and cylinders subjected to bending load. Copyright 2012 by the International Society of Offshore and Polar Engineers (ISOPE).
