Abstract
Most of the offshore platforms in the world are designed as steel jacket-type platforms for oil and gas exploration and production. A significant amount of research has been carried out over the past two decades to understand ageing and the associated degradation of offshore structural members. The paper proposes an approach for prioritization and preventive maintenance of jacket-type platform. Offshore platform maintenance systems are dependent on deterioration models to predict the future condition of structural elements. The input for these models consists of condition states of different jacket elements and their evolution as a function of time. One of the challenges includes lack of availability of condition state records for the aging platforms. This paper proposes a methodology for developing deterioration models when there is a scarcity of inspection records.
This study focusses on developing a methodology for i) the impact ranking of different bracing member groups of the jacket platform and ii) deterioration models using integrated probabilistic-mechanistic modeling. Firstly, a typical jacket-type offshore platform under the North Sea conditions is modeled and analyzed under wave and current loads. Then, nonlinear static (pushover) analyses are performed for the undamaged jacket platform. The criticality of the different groups of bracing elements is obtained in terms of Residual Resistance Factor by carrying-out redundancy analyses. Soil-structure interaction effect is considered in the analyses and the results are compared with the hypothetical fixed-support end condition. The member groups are then ranked based on their impact on the ultimate strength of the jacket platform. Secondly, deterioration models for jacket legs and bracings in splash and immersion zones are obtained based on integrated mechanistic-probabilistic approach. An idealized uniform corrosion model is used in generating the member condition state probabilities. Condition state probabilities for jacket legs and bracings are then generated using Monte Carlo simulations. The residual service life of the jacket elements is predicted from the deterioration models which could be utilized for preventive maintenance of the jacket platform.
