| Due to constantly being seawater corrosion and changing environmental load, the structure of jacket platform being in the service process, will have a variety of damage, such as cracks, corrosion, and so on. These injuries may be the cause of the jacket platform overall structural damage. In recent years, China has a considerable number of jacket platform with service period nearing its design life, and detected cracks, its fracture assessment and fatigue life prediction becomes a serious problem. For example, currently, many jacket platforms of CNOOC(China National Offshore Oil Corporation) being in service for a long time in the wave loads, most platforms have appeared fatigue cracks.Offshore jacket platform is a typical welding structure. Such failure of welded structures, mostly caused by fatigue of welded joints, and mostly occurs in the jacket joints area. Fatigue failure of the tubular joint is mainly due to an external periodically repeated loading effect results. Pile foundation structure jacket platform under wave loads, although conducting the overall structural analysis, the required stress is far below the yield strength of the material, but because of the stress concentration at the tubular joint, resulting in high local stresses under repeated wave load, weld defects of tubular at the nodes and the tiny crack formation will gradually expand, leading to the occurrence of the crack pipe fracture failure node. In order to quantitatively assess cracks, it can evidence-basely maximize the potential of managed nodes, extend the service period of the jacket platform.This paper uses a combination of fatigue analysis and fracture mechanics approach, based on BS7910 specifications, API RP 2A specification, Norsok Standard-N004 specification conducting fracture assessment and predicting fatigue life for existing crack on jacket offshore platform. Fracture and fatigue analysis software for jacket platform is completely programmed. The software applied to perform engineering critical assessment of fracture(ECA) and fracture mechanics-based fatigue life prediction for the typical tubular joints on jacket platform. |
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