Requalification of offshore structures

The project has been divided into two phases. In the first phase all design parameters for offshore steel structures and pipelines have been studied, the most important design parameters have been identified, and improved probabilistic models for these parameters have been developed. In the second phase the probabilistic models have been integrated into economical decision models where all the financial aspects involved are included and all significant parameters and uncertainties are modelled as stochastic variables/processes. In the project a new joint-probability model has been developed for determination of design parameters for waves, current, water levels, and wind velocities. A consistent model for determination of directional distributions for design waves has also been developed. Furthermore new short-term distributions for maximum individual wave and crest heights have been determined. The probabilistic models for the design parameters have been integrated into economical decision models. These models have then been used to study optimal extension of the economical life of offshore structures, optimal inspection of offshroe structures for cracks, and optimal prevention of upheaval buckling for hot pipelines. Approximate methods for probabilistic inspection planning of offshore structures which take into account the consequences of possible cracks due to fatigue have been formulated and representative examples have been studied. These methods can be used to simplify the inspection planning by means of generic inspection planning for a number of typical design situations. The results of the project have been documented in a number of reports and conference papers