Spud Can Cracking Root Cause Analysis

The Spudcan structure on an accommodation jack-up was showing regular through thickness cracks at the leg/can interface and requiring expensive repair and replacement operations at every dry-dock.

Longitude was requested to perform a root-cause analysis to determine the cause of the cracking and then suggest methods of extending the life. A detailed finite element model was created to represent the spudcan structure and lower extent of the leg. In order to accurately assess the stresses in the spudcan, the top of the leg was restrained and the forces and moments representing the soil interactions were applied as distributed loads to the base of the spudcan. A range of soil conditions/resistances could be considered by balancing the net base shear and over-turning moments applied to the base to a level of resistance.

The stress hot-spots in the FEA showed a very good correlation with the cracking locations, allowing the causes and remedies to be investigated further. This analysis showed that the cracking was caused primarily by large overturning moments when the spudcan was being used on different soil types to the original design. Longitude specified local repairs and strengthening to extend the life and also performed global analysis and redesign of the spudcan structure to suit the conditions more appropriately.