Usually, it is the welds which develop the cracks first that then propagates to the rest of the structure.
In some cases, the vibrational loads of the structure may also result in fatigue.
It is estimated that over a lifetime of 20 years, an offshore structure will experience 10 8 cycles of stress. This phenomenon is called ‘fatigue cracking’. Over a short period of a few months, this cyclical variation of stress doesn’t affect the structure, but over the lifetime of the vessel, constantly experiencing cyclical stresses may lead to cracks in the structure. These cyclical loads result in cyclical stresses on the structure too.
By their nature, the resulting wave loads on the structure are cyclical. A simplified method of performing fatigue analysis of offshore structuresĪn offshore structure is subject to environmental loads of waves, wind and current.
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